Regulation of BCR-mediated Ca2+ mobilization by MIZ1-TMBIM4 safeguards IgG1+ GC B cell-positive selection

The transition from immunoglobulin M (IgM) to affinity-matured IgG antibodies is vital for effective humoral immunity. This is facilitated by germinal centers (GCs) through affinity maturation and preferential maintenance of IgG+ B cells over IgM+ B cells. However, it is not known whether the positive selection of the different Ig isotypes within GCs is dependent on specific transcriptional mechanisms. Here, we explored IgG1+ GC B cell transcription factor dependency using a CRISPR-Cas9 screen and conditional mouse genetics. We found that MIZ1 was specifically required for IgG1+ GC B cell survival during positive selection, whereas IgM+ GC B cells were largely independent. Mechanistically, MIZ1 induced TMBIM4, an ancestral anti-apoptotic protein that regulated inositol trisphosphate receptor (IP3R)-mediated calcium (Ca2+) mobilization downstream of B cell receptor (BCR) signaling in IgG1+ B cells. The MIZ1-TMBIM4 axis prevented mitochondrial dysfunction-induced IgG1+ GC cell death caused by excessive Ca2+ accumulation. This study uncovers a unique Ig isotype-specific dependency on a hitherto unidentified mechanism in GC-positive selection.

Inhibition of HDAC6 promotes microvascular endothelial cells to phagocytize myelin debris and reduces inflammatory response to accelerate the repair of spinal cord injury

AIMS

To identify an effective strategy for promoting microvascular endothelial cells (MECs) to phagocytize myelin debris and reduce secretion of inflammatory factors following spinal cord injury (SCI).

METHODS

We established a coculture model of myelin debris and vascular-like structures. The efficiency with which MECs phagocytize myelin debris under different conditions was examined via ELISA, flow cytometry, and immunofluorescence. Tubastatin-A was used to interfere with the coculture model. The anti-inflammatory effects of Tubastatin-A were observed by HE staining, flow cytometry, immunofluorescence, and ELISA.

RESULTS

MECs phagocytized myelin debris via IgM opsonization, and phagocytosis promoted the secretion of inflammatory factors, whereas IgG-opsonized myelin debris had no effect on inflammatory factors. Application of the HDAC6 inhibitor Tubastatin-A increased the IgG levels and decreased the IgM levels by regulating the proliferation and differentiation of B cells. Tubastatin-A exerted a regulatory effect on the HDAC6-mediated autophagy-lysosome pathway, promoting MECs to phagocytize myelin debris, reducing the secretion of inflammatory factors, and accelerating the repair of SCI.

CONCLUSIONS

Inhibition of HDAC6 to regulate the immune-inflammatory response and promote MECs to phagocytize myelin debris may represent a novel strategy in the treatment of SCI.

Chlorella vulgaris extract conjugated magnetic iron nanoparticles in nile tilapia (Oreochromis niloticus): Growth promoting, immunostimulant and antioxidant role and combating against the synergistic infection with Ichthyophthirius multifiliis and Aeromonashydrophila

Nile tilapia reared under intensive conditions was more susceptible for Ichthyophthirius multifilii (I. multifiliis) infection eliciting higher mortality, lower productive rate and further bacterial coinfection with Aeromonas hydrophila (A. hydrophila). The higher potency of magnetic field of iron oxide nanoparticles (NPs) can kill pathogens through inhibiting their viability. Herein, coating of Chlorella vulgaris extract (ChVE) with magnetic iron oxide NPs (Mag iron NPs) can create an external magnetic field that facilitates their release inside the targeted tissues. Thus, the current study is focused on application of new functionalized properties of Mag iron NPs in combination with ChVE and their efficacy to alleviate I. multifiliis and subsequent infection with A. hydrophila in Nile tilapia. Four hundred fingerlings were divided into: control group (with no additives), three groups fed control diet supplemented with ChVE, Mag iron NPs and ChVE@Mag iron NPs for 90 days. At the end of feeding trial fish were challenged with I. multifiliis and at 9 days post challenge was coinfected by A. hydrophila. A remarkable higher growth rate and an improved feed conversion ratio were detected in group fed ChVE@Mag iron-NPs. The maximum expression of antioxidant enzymes in skin and gills tissues (GSH-Px, CAT, and SOD) which came in parallel with higher serum activities of these enzymes was identified in groups received ChVE@Mag iron-NPs. Furthermore, group fed a combination of ChVE and Mag iron-NPs showed a boosted immune response (higher lysozyme, IgM, ACH50, and MPO) prior to challenge with I. multifiliis. In contrast, fish fed ChVE@Mag iron-NPs supplemented diet had lower infection (decreased by 62%) and mortality rates (decreased by 84%), as well as less visible white spots (decreased by 92 % at 12 dpi) on the body surfaces and mucous score. Interestingly, post I. multifiliis the excessive inflammatory response in gill and skin tissues was subsided by feeding on ChVE@Mag iron-NPs as proved by down regulation of IL-1β, TNFα, COX-2 and iNOS and upregulation of IL-10, and IgM, IgT and Muc-2 genes. Notably, group exposed to I. multifiliis-showed higher mortality when exposed to Aeromonas hydrophilia (increased by 43 %) while group fed ChVE@Mag iron-NPs exhibited lower morality (2%). Moreover, the bacterial loads of A. hydrophilia in fish infected by I. multifiliis and fed control diet were higher than those received dietary supplement of ChVE, Mag iron-NPs and the most reduced load was obtained in group fed ChVE@Mag iron-NPs at 7 dpi. In conclusion, ChVE@Mag iron-NPs fed fish had stronger immune barrier and antioxidant functions of skin and gills, and better survival following I. multifiliis and A. hydrophilia infection.

Dietary supplementation with pseudostellaria heterophylla polysaccharide enhanced immunity and changed mRNA expression of spleen in chicks

In recent years, increasing interest has focused on natural components extracted from plants, among which plant polysaccharides as natural immunomodulators that can promote animal immunity. The present study was performed to investigate the effect of feed supplement Pseudostellaria Heterophylla Polysaccharide (PHP) on serum Immunoglobulins, T lymphocyte subpopulations, Cytokines and Lysozyme (LZM) activity in chicks. In addition, the influence of PHP on splenic gene expression was investigated by transcriptome sequencing. Four hundred 7-day-old Gushi cocks were randomly divided into four groups in a completely randomized design. The chicks were fed with a basal diet supplemented with 0 (CON-A), 100 (PHP-L), 200 (PHP-M) and 400 (PHP-H) mg/kg PHP. Blood and spleen samples were collected from 6 randomly selected chicks in each group at 14, 21, 28, and 35 days of age. The results showed that compared to the CON-A group, the PHP-M group exhibited significant increases in the levels of IgA, IgG, IgM, CD3, and LZM in the serum at 14, 21, 28, and 35 days (P < 0.05), and at 28 d, there was a significant quadratic relationship between the levels of dietary PHP and the levels of IgG, IgM, IFN-γ, IL-2, CD3, and LZM. Furthermore, a total of 470 differentially expressed genes (DEGs) were identified in spleen from PHP-M and CON-A at 28 d. These DEGs were significantly enriched in the Phagosome, Intestinal immune network for IgA production and Cytokine-cytokine receptor interaction pathways. The present investigation highlights the ameliorating effect of dietary PHP on immunological variables and spleen of chicks, the study suggests that PHP supplementation can enhance immunity and positively impact spleen mRNA expression in chicks.

Secreted IgM modulates IL-10 expression in B cells

IL-10+ B cells are critical for immune homeostasis and restraining immune responses in infection, cancer, and inflammation; however, the signals that govern IL-10+ B cell differentiation are ill-defined. Here we find that IL-10+ B cells expand in mice lacking secreted IgM ((s)IgM-/-) up to 10-fold relative to wildtype (WT) among all major B cell and regulatory B cell subsets. The IL-10+ B cell increase is polyclonal and presents within 24 hours of birth. In WT mice, sIgM is produced prenatally and limits the expansion of IL-10+ B cells. Lack of the high affinity receptor for sIgM, FcμR, in B cells translates into an intermediate IL-10+ B cell phenotype relative to WT or sIgM-/- mice. Our study thus shows that sIgM regulates IL-10 programming in B cells in part via B cell-expressed FcμR, thereby revealing a function of sIgM in regulating immune homeostasis.

Liver macrophages and sinusoidal endothelial cells execute vaccine-elicited capture of invasive bacteria

Vaccination has substantially reduced the morbidity and mortality of bacterial diseases, but mechanisms of vaccine-elicited pathogen clearance remain largely undefined. We report that vaccine-elicited immunity against invasive bacteria mainly operates in the liver. In contrast to the current paradigm that migrating phagocytes execute vaccine-elicited immunity against blood-borne pathogens, we found that invasive bacteria are captured and killed in the liver of vaccinated host via various immune mechanisms that depend on the protective potency of the vaccine. Vaccines with relatively lower degrees of protection only activated liver-resident macrophage Kupffer cells (KCs) by inducing pathogen-binding immunoglobulin M (IgM) or low amounts of IgG. IgG-coated pathogens were directly captured by KCs via multiple IgG receptors FcγRs, whereas IgM-opsonized bacteria were indirectly bound to KCs via complement receptors of immunoglobulin superfamily (CRIg) and complement receptor 3 (CR3) after complement C3 activation at the bacterial surface. Conversely, the more potent vaccines engaged both KCs and liver sinusoidal endothelial cells by inducing higher titers of functional IgG antibodies. Endothelial cells (ECs) captured densely IgG-opsonized pathogens by the low-affinity IgG receptor FcγRIIB in a "zipper-like" manner and achieved bacterial killing predominantly in the extracellular milieu via an undefined mechanism. KC- and endothelial cell-based capture of antibody-opsonized bacteria also occurred in FcγR-humanized mice. These vaccine protection mechanisms in the liver not only provide a comprehensive explanation for vaccine-/antibody-boosted immunity against invasive bacteria but also may serve as in vivo functional readouts of vaccine efficacy.

CD5L is a canonical component of circulatory IgM

Immunoglobulin M (IgM) is an evolutionary conserved key component of humoral immunity, and the first antibody isotype to emerge during an immune response. IgM is a large (1 MDa), multimeric protein, for which both hexameric and pentameric structures have been described, the latter additionally containing a joining (J) chain. Using a combination of single-particle mass spectrometry and mass photometry, proteomics, and immunochemical assays, we here demonstrate that circulatory (serum) IgM exclusively exists as a complex of J-chain-containing pentamers covalently bound to the small (36 kDa) protein CD5 antigen-like (CD5L, also called apoptosis inhibitor of macrophage). In sharp contrast, secretory IgM in saliva and milk is principally devoid of CD5L. Unlike IgM itself, CD5L is not produced by B cells, implying that it associates with IgM in the extracellular space. We demonstrate that CD5L integration has functional implications, i.e., it diminishes IgM binding to two of its receptors, the FcαµR and the polymeric Immunoglobulin receptor. On the other hand, binding to FcµR as well as complement activation via C1q seem unaffected by CD5L integration. Taken together, we redefine the composition of circulatory IgM as a J-chain containing pentamer, always in complex with CD5L.

Polysarcosine-Coated liposomes attenuating immune response induction and prolonging blood circulation

HYPOTHESIS

Liposomes coated with long polysarcosine (PSar) chains at a high density might enable long blood circulation and attenuate accelerated blood clearance (ABC) phenomenon.

EXPERIMENTS

In this study, we controlled the length (23, 45, 68 mers) and density (5, 10, 15 mol%) of PSar on liposomal coatings and, furthermore, investigated the effects of PSar length and density on the blood circulation time, biodistribution, immune response, and ABC phenomenon induction. Length-controlled PSar-bound lipids (PSar-PEs) were synthesized using a click reaction and inserted into bare liposomes at different combinations of chain lengths and proportions.

FINDINGS

Although all PSar-coated liposomes (PSar-lipos) had similar morphological, physical, and chemical properties, they had different blood circulation times and biodistribution, and exerted varied effects on the immune system. All PSar-lipos with different PSar length and density showed a similar anti-PSar IgM response. Liposomes modified with the longest PSar chain (68 mers) at a high density (15 mol%) showed the longest blood circulation time and, additionally, attenuated ABC phenomenon compared with PEG-lipo. The ex vivo analysis of the biodistribution of liposomes revealed that a thick PSar layer enhanced the blood circulation time of liposomes due to the reduction of the accumulation of liposomes in the liver and spleen. These findings provide new insights into the relationship between IgM expression and ABC phenomenon inhibition.

Molecular characterization of the B lymphocyte-induced maturation protein-1 (blimp1) gene of common carp (Cyprinus carpio) and its transcription repression involves recruitment of histone deacetylase HDAC3

Blimp1 is the master regulator of B cell terminal differentiation in mammals, it inhibits expression of many transcription factors including bcl6, which provides the basis for promoting further development of activated B lymphocytes into plasma cells. Blimp-1 is thought to act as a sequence-specific recruitment factor for chromatin-modifying enzymes including histone deacetylases (HDAC) and methyltransferases to repress target genes. The cDNA of Ccblimp1a (Cyprinus carpio) open reading frame is 2337 bp encoding a protein of 777 amino acids. CcBlimp1a contains a SET domain, two Proline Rich domains, and five ZnF_C2H2 domains. Blimp1 are conserved in vertebrate species. Ccblimp1a transcripts were detected in common carp larvae from 1 dpf (day post fertilization)to 31 dpf. Ccblimp1a expression was up-regulated in peripheral blood leukocytes (PBL) and spleen leukocytes (SPL) of common carp stimulated by intraperitoneal lipopolysaccharide (LPS) injection. Ccblimp1a expression in PBL and SPL of common carp was induced by TNP-LPS and TNP-KLH. The results indicated TNP-LPS induced a rapid response in PBL and TNP-KLH induced much stronger response in SPL and PBL. IHC results showed that CcBlimp1 positive cells were distributed in the head kidney, trunk kidney, liver, and gut. Immunofluorescence stain results showed that CcBlimp1 was expressed in IgM + lymphocytes. The subcellular localization of CcBlimp1 in the nuclei indicated CcBlimp1 may be involved in the differentiation of IgM + lymphocytes. Further study focusing on the function of CcBlimp1 transcriptional repression was performed using dual luciferase assay. The results showed that the transcription repression of CcBlimp1 on bcl6aa promoter was affected by the histone deacetylation inhibitor and was synergized with histone deacetylase 3 (HDAC3). The results of Co-IP in HEK293T and immunoprecipitation in SPL indicated that CcBlimp1 recruited HDAC3 and might be involved in the formation of complexes. These results suggest that CcBlimp1 is an important transcription factor in common carp lymphocytes. Histone deacetylation modification mediated by HDAC3 may have important roles in CcBlimp1 transcriptional repression during the differentiation of lymphocytes.

Artificial surface labelling of Escherichia coli with StrepTagII antigen to study how monoclonal antibodies drive complement-mediated killing

Antibodies play a key role in the immune defence against Gram-negative bacteria. After binding to bacterial surface antigens, IgG and IgM can activate the complement system and trigger formation of lytic membrane attack complex (MAC) pores. Molecular studies to compare functional activity of antibodies on bacteria are hampered by the limited availability of well-defined antibodies against bacterial surface antigens. Therefore, we genetically engineered E. coli by expressing the StrepTagII antigen into outer membrane protein X (OmpX) and validated that these engineered bacteria were recognised by anti-StrepTagII antibodies. We then combined this antigen-antibody system with a purified complement assay to avoid interference of serum components and directly compare MAC-mediated bacterial killing via IgG1 and pentameric IgM. While both IgG1 and IgM could induce MAC-mediated killing, we show that IgM has an increased capacity to induce complement-mediated killing of E. coli compared to IgG1. While Fc mutations that enhance IgG clustering after target binding could not improve MAC formation, mutations that cause formation of pre-assembled IgG hexamers enhanced the complement activating capacity of IgG1. Altogether, we here present a system to study antibody-dependent complement activation on E. coli and show IgM's enhanced capacity over IgG to induce complement-mediated lysis of E. coli.

Cryo-electron microscopy of IgM-VAR2CSA complex reveals IgM inhibits binding of Plasmodium falciparum to Chondroitin Sulfate A

Placental malaria is caused by Plasmodium falciparum-infected erythrocytes (IEs) adhering to chondroitin sulfate proteoglycans in placenta via VAR2CSA-type PfEMP1. Human pentameric immunoglobulin M (IgM) binds to several types of PfEMP1, including VAR2CSA via its Fc domain. Here, a 3.6 Å cryo-electron microscopy map of the IgM-VAR2CSA complex reveals that two molecules of VAR2CSA bind to the Cµ4 of IgM through their DBL3X and DBL5ε domains. The clockwise and anti-clockwise rotation of the two VAR2CSA molecules on opposite faces of IgM juxtaposes C-termini of both VAR2CSA near the J chain, where IgM creates a wall between both VAR2CSA molecules and hinders its interaction with its receptor. To support this, we show when VAR2CSA is bound to IgM, its staining on IEs as well as binding of IEs to chondroitin sulfate A in vitro is severely compromised.

L-methionine supplementation modulates IgM+ B cell responses in rainbow trout

The interest in dietary amino acids (AAs) as potential immunomodulators has been growing the recent years, since specific AAs are known to regulate key metabolic pathways of the immune response or increase the synthesis of some immune-related proteins. Methionine, tryptophan and lysine are among the ten essential AAs for fish, meaning that they cannot be produced endogenously and must be provided through the diet. To date, although dietary supplementation of fish with some of these AAs has been shown to have positive effects on some innate immune parameters and disease resistance, the effects that these AAs provoke on cells of the adaptive immune system remained unexplored. Hence, in the current study, we have investigated the effects of these three AAs on the functionality of rainbow trout (Oncorhynchus mykiss) IgM+ B cells. For this, splenic leukocytes were isolated from untreated adult rainbow trout and incubated in culture media additionally supplemented with different doses of methionine, tryptophan or lysine in the presence or absence of the model antigen TNP-LPS (2,4,6-trinitrophenyl hapten conjugated to lipopolysaccharide). The survival, IgM secreting capacity and proliferation of IgM+ B cells was then studied. In the case of methionine, the phagocytic capacity of IgM+ B cells was also determined. Our results demonstrate that methionine supplementation significantly increases the proliferative effects provoked by TNP-LPS and also up-regulates the number of cells secreting IgM, whereas tryptophan or lysine have either minor or even negative effects on rainbow trout IgM+ B cells. This increase in the number of IgM-secreting cells in response to methionine surplus was further verified in a feeding experiment, in which the beneficial effects of methionine on the specific response to anal immunization were also confirmed. The results presented demonstrate the beneficial effects of dietary supplementation with methionine on the adaptive immune responses of fish.

Anti-inflammatory activity of novel derivatives of pyrazolo [3,4d] pyridazine against digestive system inflammation

The digestive system is exposed to severe inflammation as a result of taking some medications that have gastrointestinal side effects. Sixty Swiss-albino male mice were randomly distributed into six groups to treat inflammations of the colon, stomach, and small intestine caused by taking high doses of diclofenac (D), with two novel synthesized compounds, pyrazolo [3,4 d] pyridazine derivatives (Co1 and Co2). Myeloperoxidase enzyme activity was determined in the colon and small intestinal tissues. Serum contents of TNF-α, IL-22, IgG, and IgM were determined by ELISA. Histopathological examinations of the colon, small intestinal, and stomach tissues were microscopically analyzed. TNF-α, IL-22, and TNFSF11 gene expression were measured in the colon, intestinal, and spleen using qRT-PCR. Diclofenac caused surface columnar epithelial cell loss, focal necrosis of the gastric mucosa, inflammatory cell infiltration, and congested blood vessels in the stomach, colon, and small intestinal tissues. Co1 component was found to be better than Co2 component in reducing the focal necrosis of gastric mucosa and improving the histological structures of the stomach, colon, and small intestinal tissues. After 14 days, the activity of the myeloperoxidase enzyme was increased in group D and decreased in groups DCo1, DCo2, Co1, and Co2. Serum concentrations of TNF-α and IgG were increased, while IL-22 and IGM were reduced in the D, DCo1, and DCo2 groups compared with the Co1 and control groups. TNF-α gene was upregulated in the D group and downregulated in the Co1 group, while the IL-22 gene was downregulated in the D group and upregulated in the Co1 group compared with the control group. The CO1 component may be useful in reducing digestive system inflammation.

Biological responses of stellate sturgeon fingerlings (Acipenser stellatus) immersed in HSP inducer to salinity changes

Changes in salinity is a stressful and energy-consuming process in fish which give rise to mortalities, especially in fish fingerlings that are more sensitive during the early stages of their life. In the present study, the effects of three salinities, 3‰ (downstream of river), 8‰ (estuarine), and 13‰ (the maximum salinity in the Caspian Sea), on HSP70 gene expression, cortisol level, immune response (lysozyme, complement C3, IgM), and antioxidant enzyme activities (SOD, CAT, T-AOC) of the stellate sturgeon fingerlings in the presence of HSP inducer compound (TEX-OE®) were evaluated. Our results showed that levels of plasma cortisol and heat shock protein (HSP70) in Acipenser stellatus fingerlings increased due to salinity changes. In the presence of the HSP inducer, HSP70 expression in both gill and liver was significantly increased, whereas cortisol level was notably decreased. Exposure to salinity changes resulted in an increase in antioxidant defense activities (SOD, CAT, and T-AOC) and immune response (lysozyme, IgM, and C3) in the presence of an HSP inducer. In conclusion, an HSP-inducing compounds can have a positive effect in strengthening the immunity and antioxidant system of sturgeon fingerlings by increasing the expression of the HSP70 gene against salinity fluctuations and generally increase the body's physiological tolerance.

Contribution of ADD3 and the HLA Genes to Biliary Atresia Risk in Chinese

Nonsyndromic biliary atresia (BA) is a rare polygenic disease, with autoimmunity, virus infection and inflammation thought to play roles in its pathogenesis. We conducted a genome-wide association study in 336 nonsyndromic BA infants and 8900 controls. Our results validated the association of rs17095355 in ADD3 with BA risk (odds ratio (OR) = 1.70, 95% confidence interval (95% CI) = 1.49-1.99; p = 4.07 × 10-11). An eQTL analysis revealed that the risk allele of rs17095355 was associated with increased expression of ADD3. Single-cell RNA-sequencing data and immunofluorescence analysis revealed that ADD3 was moderately expressed in cholangiocytes and weakly expressed in hepatocytes. Immuno-fluorescent staining showed abnormal deposition of ADD3 in the cytoplasm of BA hepatocytes. No ADD3 auto-antibody was observed in the plasma of BA infants. In the HLA gene region, no variants achieved genome-wide significance. HLA-DQB1 residue Ala57 is the most significant residue in the MHC region (OR = 1.44, 95% CI = 1.20-1.74; p = 1.23 × 10-4), and HLA-DQB1 was aberrantly expressed in the bile duct cells. GWAS stratified by cytomegalovirus (CMV) IgM status in 87 CMV IgM (+) BA cases versus 141 CMV IgM (-) BA cases did not yield genome-wide significant associations. These findings support the notion that common variants of ADD3 account for BA risk. The HLA genes might have a minimal role in the genetic predisposition of BA due to the weak association signal. CMV IgM (+) BA patients might not have different genetic risk factor profiles compared to CMV IgM (-) subtype.

Biochemical Characterization of a New 10% IVIG Preparation [IgG Next Generation (BT595)/Yimmugo®] Obtained from a Manufacturing Process Preserving IgA/IgM Potential of Human Plasma

BACKGROUND AND OBJECTIVE

Human plasma is used for the generation of several life-saving drugs and contains valuable antibodies from the immunoglobulin classes IgG, IgM and IgA. Purified intravenous IgG solutions (IVIGs) form the majority of plasma-derived medicine to treat patients with various forms of immunodeficiencies. In conventional IVIG manufacturing processes, immunoglobulin classes IgM and IgA are often discarded as contaminants, but these antibody classes have been proven to be effective for the treatment of acute bacterial infections. Considering the increase in demand for human plasma-derived products and the ethical value of the raw material, a more resource-saving usage of human plasma is needed. Intensive research over the last decades showed that adverse reactions to IVIGs depend on the presence of thrombogenic factors, partially unfolded proteins, non-specific activation of the complement system, and blood group specific antibodies. Therefore, new IVIG preparations with reduced risks of adverse reactions are desirable.

METHOD

A new manufacturing process that yields two biologics was established and quality attributes of the new IVIG solution (Yimmugo®) obtained from this process are presented.

RESULTS

Here, we provide a biochemical characterization of Yimmugo®, a new 10% IVIG preparation. It is derived from human blood plasma by a combined manufacturing process, where IgM and IgA are retained for the production of a new biologic (trimodulin, currently under investigation in phase III clinical trials). Several improvements have been implemented in the manufacturing of Yimmugo® to reduce the risk of adverse reactions. Gentle and efficient mixing by vibration (called "vibromixing") during a process step where proteins are at risk to aggregate was implemented to potentially minimize protein damage. In addition, a dedicated process step for the removal of the complement system activator properdin was implemented, which resulted in very low anticomplementary activity levels. The absence of measurable thrombogenic activity in combination with a very high degree of functional monomeric antibodies predict excellent efficacy and tolerability.

CONCLUSION

Yimmugo® constitutes a new high quality IVIG preparation derived from a novel manufacturing process that takes advantage of the full therapeutic immunoglobulin potential of human plasma.

Interaction of Iron Homeostasis and Fatty Acid Metabolism in the Development of Glucose Intolerance in Women with Previous Gestational Diabetes Mellitus

A gestational diabetes mellitus (GDM) diagnosis during pregnancy means an increased risk of developing type 2 diabetes later in life. By following up with women after GDM we aimed to examine the relationship between iron parameters, individual fatty acids (FAs) and desaturases in the development of impaired glucose metabolism (IGM). Based on an oral glucose tolerance test (OGTT), six years after GDM, 157 women were grouped as having normal glucose tolerance (NGT) or IGM. Fasting serum FAs, activity of desaturases and iron parameters (ferritin, transferrin, iron, soluble transferrin receptor, total iron binding capacity, hepcidin) were measured, and clinical and anthropometric measurements taken. Soluble transferrin receptor was higher in the IGM group compared to the NGT group (3.87 vs. 3.29 mg/L, p-value = 0.023) and associated positively with saturated FAs and negatively with monounsaturated FAs in the IGM group (adjusted for BMI, age and high sensitivity C-reactive protein; p-value < 0.05). Iron, as well as transferrin saturation, showed a positive association with MUFAs and desaturase activity. These associations were not seen in the NGT group. These results suggest that iron homeostasis and FA metabolism interact in the development of glucose intolerance in women with previous GDM.

Enhanced Mott cell formation linked with IgM Fc receptor (FcμR) deficiency

In previous studies, Mott cells, an unusual form of plasma cells containing Ig-inclusion bodies, were frequently observed in peripheral lymphoid tissues in our IgM Fc receptor (FcμR)-deficient (KO) mouse strain. Because of discrepancies in the reported phenotypes of different Fcmr KO mouse strains, we here examined two additional available mutant strains and confirmed that such enhanced Mott-cell formation was a general phenomenon associated with FcμR deficiency. Splenic B cells from Fcmr KO mice clearly generated more Mott cells than those from WT mice when stimulated in vitro with LPS alone or a B-1, but not B-2, activation cocktail. Nucleotide sequence analysis of the Ig variable regions of a single IgMλ+ Mott-hybridoma clone developed from splenic B-1 B cells of Fcmr KO mice revealed the near (VH) or complete (Vλ) identity with the corresponding germline gene segments and the addition of six or five nucleotides at the VH/DH and DH/JH junctions, respectively. Transduction of an FcμR cDNA into the Mott hybridoma significantly reduced cells containing IgM-inclusion bodies with a concomitant increase in IgM secretion, leading to secreted IgM binding to FcμR expressed on Mott transductants. These findings suggest a regulatory role of FcμR in the formation of Mott cells and IgM-inclusion bodies.

Characterization of T-cell receptors and immunoglobulin heavy chains loci and identification of T/B cell clusters in teleost

Bacterial disease is one of the important factors leading to economic losses in the turbot (Scophthalmus maximus) cultivation industry. T lymphocytes are major components of cellular immunity, whereas B lymphocytes produce immunoglobulins (Ig) that are key elements of humoral immune responses against infection. However, the genomic organization of genes encoding T-cell receptors (TCR) and immunoglobulin heavy chains (IgHs) in turbot remains largely unknown. In this study, abundant full-length transcripts of TCRs and IgHs were sequenced by Isoform-sequencing (Iso-seq), and we investigated and annotated the V, D, J and C gene loci of TCRα, TCRβ, IgT, IgM and IgD in turbot. Furthermore, through single-cell RNA sequencing (scRNA-seq) of blood leukocytes, we confirmed that these identified TCRs and IgHs were highly expressed in T/B cell clusters, respectively. Meanwhile, we also identified the IgM⁺IgD⁺ B and IgT⁺ B cells with differential gene expression profiles and potential functions. Taken together, our results provide a comprehensive understanding of TCRs and IgHs loci in turbot, which will contribute to evolutionary and functional characterization of T and B lymphocytes in teleost.

Glutamine Metabolism Underlies the Functional Similarity of T Cells between Nile Tilapia and Tetrapod

As the lowest organisms possessing T cells, fish are instrumental for understanding T cell evolution and immune defense in early vertebrates. This study established in Nile tilapia models suggests that T cells play a critical role in resisting Edwardsiella piscicida infection via cytotoxicity and are essential for IgM⁺ B cell response. CD3 and CD28 monoclonal antibody crosslinking reveals that full activation of tilapia T cells requires the first and secondary signals, while Ca²⁺ -NFAT, MAPK/ERK, NF-κB, and mTORC1 pathways and IgM⁺ B cells collectively regulate T cell activation. Thus, despite the large evolutionary distance, tilapia and mammals such as mice and humans exhibit similar T cell functions. Furthermore, it is speculated that transcriptional networks and metabolic reprogramming, especially c-Myc-mediated glutamine metabolism triggered by mTORC1 and MAPK/ERK pathways, underlie the functional similarity of T cells between tilapia and mammals. Notably, tilapia, frogs, chickens, and mice utilize the same mechanisms to facilitate glutaminolysis-regulated T cell responses, and restoration of the glutaminolysis pathway using tilapia components rescues the immunodeficiency of human Jurkat T cells. Thus, this study provides a comprehensive picture of T cell immunity in tilapia, sheds novel perspectives for understanding T cell evolution, and offers potential avenues for intervening in human immunodeficiency.

Report of consensus Panel 4 from the 11th International Workshop on Waldenstrom's macroglobulinemia on diagnostic and response criteria

Consensus Panel 4 (CP4) of the 11th International Workshop on Waldenstrom's Macroglobulinemia (IWWM-11) was tasked with reviewing the current criteria for diagnosis and response assessment. Since the initial consensus reports of the 2nd International Workshop, there have been updates in the understanding of the mutational landscape of IgM related diseases, including the discovery and prevalence of MYD88 and CXCR4 mutations; an improved recognition of disease related morbidities attributed to monoclonal IgM and tumor infiltration; and a better understanding of response assessment based on multiple, prospective trials that have evaluated diverse agents in Waldenstrom's macroglobulinemia. The key recommendations from IWWM-11 CP4 included: (1) reaffirmation of IWWM-2 consensus panel recommendations that arbitrary values for laboratory parameters such as minimal IgM level or bone marrow infiltration should not be used to distinguish Waldenstrom's macroglobulinemia from IgM MGUS; (2) delineation of IgM MGUS into 2 subclasses including a subtype characterized by clonal plasma cells and MYD88 wild-type, and the other by presence of monotypic or monoclonal B cells which may carry the MYD88 mutation; and (3) recognition of "simplified" response assessments that use serum IgM only for determining partial and very good partial responses (simplified IWWM-6/new IWWM-11 response criteria). Guidance on response determination for suspected IgM flare and IgM rebound related to treatment, as well as extramedullary disease assessment was also updated and included in this report.

Plasma membrane topography governs the 3D dynamic localization of IgM B cell antigen receptor clusters

B lymphocytes recognize bacterial or viral antigens via different classes of the B cell antigen receptor (BCR). Protrusive structures termed microvilli cover lymphocyte surfaces, and are thought to perform sensory functions in screening antigen-bearing surfaces. Here, we have used lattice light-sheet microscopy in combination with tailored custom-built 4D image analysis to study the cell-surface topography of B cells of the Ramos Burkitt's Lymphoma line and the spatiotemporal organization of the IgM-BCR. Ramos B-cell surfaces were found to form dynamic networks of elevated ridges bridging individual microvilli. A fraction of membrane-localized IgM-BCR was found in clusters, which were mainly associated with the ridges and the microvilli. The dynamic ridge-network organization and the IgM-BCR cluster mobility were linked, and both were controlled by Arp2/3 complex activity. Our results suggest that dynamic topographical features of the cell surface govern the localization and transport of IgM-BCR clusters to facilitate antigen screening by B cells.

A comparative study of effects of curcumin and its nanoparticles on the growth, immunity and heat stress resistance of Nile tilapia (Oreochromis niloticus)

This study evaluated the effects of dietary supplementation with free- or nano-curcumin on the growth performance, immune status and heat stress resistance of Nile tilapia (Oreochromis niloticus). Seven isonitrogenous (28% protein) and isocaloric (445 kcal/100 g DM) diets were prepared. Six diets were supplemented with three levels of nano-curcumin (50 (CN50), 100 (CN100), 200 (CN200) mg kg^-1 diet) or free-curcumin (50 (C50), 100 (C100), 200 (C200) mg kg^-1 diet), and the control diet was left without an additive (CON). Fish (13.54 ± 0.32 g) (mean ± SD) fed the experimental diets for 65 days. Following the feeding trial, the fish were exposed to the acute heat stress by gradually raising the water temperature from 25 to 40 °C within 3 h. The fish were then exposed to 40 °C for 4 h. Results revealed the superiority of nano-curcumin over its free-form in enhancing the growth performance, with the highest results obtained at CN100, followed by CN200. Only heat stress, not the experimental diets, increased the platelets, mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH), leukocytes and neutrophils count, while lymphocytes decreased. The CN50 and CN100 groups showed lower activity of liver enzymes (alanine aminotransferase (ALT) and aspartate aminotransferase (AST)) than the other treatments, while C200 gave the highest activity of these enzymes. The highest immunoglobulin (IgM) levels were detected in CN100, CN200, C100 and C200, followed by CN50. The C200 group showed higher levels of complement 3 and complement 4 (C3 and C4, respectively) than the other treatments. The C50 and CON groups gave the lowest values of IgM, C3 and C4. Cortisol levels were significantly lower in the CN50 and CN100 groups compared to the other groups. After the heat stress, ALT, AST, IgM, C3, C4, cortisol and glucose increased. Thus, nano-curcumin is more effective than its free-form in enhancing the resistance to heat stress, inducing innate immunity, lowering the stress indicators and promoting growth performance of Nile tilapia with the best concentration at 100 mg kg^-1 diet.

Large yellow croaker (Lrimichthys crocea) IL-2 modulates humoral immunity via the conserved JAK-STAT5 signal pathway

The terminal differentiation of B cells into plasma cells is central to the generation of protective, long-lived humoral immune responses. In mammals, interleukin-2 (IL-2) has been shown to play a role in B cell proliferation and differentiation. However, it remains unclear whether fish IL-2 is involved in B cell proliferation and differentiation. To this end, we investigated the regulatory role of IL-2 in B cell proliferation and differentiation in large yellow croaker (Larimichthys crocea). We found that L. crocea IL-2 (LcIL-2) significantly increased IgM⁺ B cells proliferation both in vivo and in vitro and facilitated IgM⁺ B cells differentiation into plasma cells. Furthermore, LcIL-2 increased the production of specific antibodies after immunization with the Vibrio alginolyticus subunit vaccine, recombinant dihydrolipoamide dehydrogenase (rDLD); simultaneous administration of LcIL-2 and rDLD prior to challenge with Vibrio parahaemolyticus or V. alginolyticus significantly increased relative percent survival. Mechanistically, LcIL-2 promoted B cell proliferation and regulated B cell differentiation by triggering the JAK-STAT5 signaling pathway. Collectively, our results demonstrated that LcIL-2 improved B cell proliferation and specific antibody production via the conserved JAK-STAT5 signaling pathway in large yellow croaker, providing valuable insights into the mechanisms underlying the IL-2-mediated regulation of the humoral immune response in fish.

Pronociceptive autoantibodies in the spinal cord mediate nociceptive sensitization, loss of function, and spontaneous pain in the lumbar disk puncture model of chronic back pain

ABSTRACT

Previously, we observed that B cells and autoantibodies mediated chronic nociceptive sensitization in the mouse tibia fracture model of complex regional pain syndrome and that complex regional pain syndrome patient antibodies were pronociceptive in fracture mice lacking mature B cells and antibodies (muMT). The current study used a lumbar spinal disk puncture (DP) model of low back pain in wild-type (WT) and muMT mice to evaluate pronociceptive adaptive immune responses. Spinal disks and cords were collected 3 weeks after DP for polymerase chain reaction and immunohistochemistry analyses. Wild-type DP mice developed 24 weeks of hindpaw mechanical allodynia and hyperalgesia, grip weakness, and a conditioned place preference response indicative of spontaneous pain, but pain responses were attenuated or absent in muMT DP mice. Spinal cord expression of inflammatory cytokines, immune cell markers, and complement components were increased in WT DP mice and in muMT DP mice. Dorsal horn immunostaining in WT DP mice demonstrated glial activation and increased complement 5a receptor expressionin spinal neurons. Serum collected from WT DP mice and injected into muMT DP mice caused nociceptive sensitization, as did intrathecal injection of IgM collected from WT DP mice, and IgM immune complexes were observed in lumbar spinal disks and cord of WT DP mice. Serum from WT tibia fracture mice was not pronociceptive in muMT DP mice and vice versa, evidence that each type of tissue trauma chronically generates its own unique antibodies and targeted antigens. These data further support the pronociceptive autoimmunity hypothesis for the transition from tissue injury to chronic musculoskeletal pain state.

Hepatopancreas toxicity and immunotoxicity of a fungicide, pyraclostrobin, on common carp

Pyraclostrobin (PYR), a strobilurin fungicide, has been widely used to control fungal diseases, posing potential risk to aquatic organisms. However, the toxic effects of PYR to fish remained largely unknown. In this study, common carp (Cyprinus carpio L.) was exposed to environmentally relevant levels of PYR (0, 0.5 and 5.0 μg/L) for 30 days to assess its chronic toxicity and potential toxicity mechanism. The results showed that long-term exposure to PYR induced hepatopancreas damage as evident by increased in serum transaminase activities (AST and ALT). Moreover, PYR exposure remarkably enhanced the expressions of hsp70 and hsp90, decreased the levels of antioxidant enzymes and biomarkers and promoted the reactive oxygen species (H₂O₂ and O₂^-) and MDA contents in carp hepatopancreas. PYR exposure also upregulated apoptosis-related genes (bax, apaf-1, caspase-3 and caspase-9) and reduced anti-apoptosis gene bcl-2 in fish hepatopancreas. Moreover, PYR exposure altered the expressions of inflammatory cytokines (IL-1β, IL-6, TNF-α and TGF-β) in the serum and hepatopancreas and the level of NF-κB p65 in the hepatopancreas. Further research indicated that PYR exposure markedly changed the levels of immune parameters (LYZ, C3, IgM, ACP and AKP) in the serum and/or hepatopancreas, indicating that chronic PYR exposure also has immunotoxicity on fish. Additionally, we found that PYR exposure upregulated p38 and jnk MAPK transcription levels, suggesting that MAPK may be play important role in PYR-induced apoptosis and inflammatory response in the hepatopancreas of common carp. In summary, PYR exposure induced oxidative stress, triggered apoptosis, inflammatory and immune response in common carp, which can help to elucidate the possible toxicity mechanism of PYR in fish.

Dietary aflatoxin B1 caused the growth inhibition, and activated oxidative stress and endoplasmic reticulum stress pathway, inducing apoptosis and inflammation in the liver of northern snakehead (Channa argus)

The purpose of this study was to investigate the effects of dietary aflatoxin B₁ (AFB₁) on growth performance and AFB₁ biotransformation, and hepatic oxidative stress, endoplasmic reticulum (ER) stress, apoptosis, and inflammation in northern snakehead (Channa argus). A total of 600 northern snakeheads (7.52 ± 0.02 g) were divided into five groups (three replicates/group) and fed the diets with AFB₁ at concentrations of 0, 50, 100, 200, and 400 ppb for 8 weeks. The results demonstrated that dietary AFB₁ (≥ 200 ppb) reduced FBW, WG, and SGR. 100, 200, and 400 ppb AFB₁ treatment groups significantly decreased the PER, CRP, C3, C4, IgM, and LYS levels in northern snakehead, while FCR was significant increased. Moreover, dietary AFB₁ (100, 200, and 400 ppb) increased cyp1a, cyp1b (except 400 ppb), and cyp3a mRNA expression levels, while reducing the GST enzymatic activity and mRNA expression levels in northern snakehead. Furthermore, AFB₁ (≥ 100 ppb) increased ROS, MDA, and 8-OHdG levels, and grp78, ire1, perk, jnk, chop, and traf2 mRNA expression levels, and decreased SOD, CAT, GSH-Px, and GSH (except 100 ppb) levels and the gene expression levels of cat, gsh-px (except 100 ppb), and Cu/Zn sod. In addition, AFB₁ (100, 200, and 400 ppb) up-regulated the cyt-c, bax, cas-3, and cas-9 mRNA levels in the liver, while down-regulating the bcl-2 expression levels. Meanwhile, the expression levels of nf-κb, tnf-α (except 100 ppb), il-1β, and il-8 in the liver were up-regulated in AFB₁ treatment groups (≥ 100 ppb), while the iκbα mRNA levels were down-regulated. In summary, dietary AFB₁ reduced growth performance and humoral immunity in northern snakehead. Meanwhile, the cyclic occurrence of oxidative stress and ER stress, and induced apoptosis and inflammation, is one of the main reasons for AFB₁-induced liver injury in the northern snakehead, which will provide valuable information and a fresh perspective for further research into AFB₁-induced liver injury in fish.

Production of a monoclonal antibody specific to sablefish (Anoplopoma fimbria) IgM and its application in ELISA, western blotting, and immunofluorescent staining

Sablefish (Anoplopoma fimbria) are an emerging aquaculture species native to the continental shelf of the northern Pacific Ocean. There is limited information on both innate and adaptive immunity for this species and new tools are needed to determine antibody response following vaccination or disease outbreaks. In this paper, a monoclonal antibody, UI-25A, specific to sablefish IgM was produced in mice. Western blotting confirmed UI-25A recognizes the heavy chain of IgM and does not cross react to proteins or carbohydrates in serum of four other teleost species. An ELISA was developed to measure Aeromonas salmonicida specific IgM in the plasma of sablefish from a previous experiment where fish were immunized with a proprietary A. salmonicida vaccine. UI-25A was used in Western blot analyses to identify immunogenic regions of A. salmonicida recognized by this specific IgM from vaccinated sablefish. Immunofluorescent staining also demonstrated the ability of UI-25A to recognize membrane-bound IgM and identify IgM + cells in the head kidney. These results demonstrate the usefulness of UI-25A as a tool to improve the understanding of antibody-mediated immunity in sablefish as well as to provide valuable information for vaccine development and expansion of aquaculture efforts for this fish species.

Selective IgA Deficiency in Spontaneously Hypertensive Rats With Gut Dysbiosis

BACKGROUND

The spontaneously hypertensive rat (SHR) is extensively used to study hypertension. Gut microbiota dysbiosis is a notable feature in SHR for reasons unknown. Immunoglobulin A (IgA) is a major host factor required for gut microbiota homeostasis. We hypothesized that inadequate IgA contributes to gut microbiota dysbiosis in SHR.

METHODS

IgA was measured in feces, cecum, serum, liver, gut-associated lymphoid tissue, and milk from SHR and Wistar Kyoto rats. IgA regulatory factors like IgM, IgG, and pIgR (polymeric immunoglobulin receptor) were analyzed. IgA and IgG antibodies and blood pressure (BP) were measured before and after administrating a bacterial antigen (ie, flagellin).

RESULTS

Compared with Wistar Kyoto rats, SHR displayed remarkably near-deficient IgA levels accompanied by compensatory increases in serum IgM and IgG and gut-liver pIgR expression. Inadequate milk IgA in SHR emphasized this immune defect stemmed from the neonatal stage. Reduced IgA+ B cells in circulation and Peyer patches indicated a possible reason for the lower IgA in SHR. Noteworthy, a genetic insufficiency was unlikely because administering flagellin to SHR induced anti-flagellin IgA antibodies. This immune response surprisingly accelerated hypertension development in SHR, suggesting IgA quiescence may help maintain lower BP.

CONCLUSIONS

This study is the first to reveal IgA deficiency in SHR as one host factor associated with gut microbiota dysbiosis and invigorates future research to determine the pathophysiological role of IgA in hypertension.

Will previous palliative surgery for congenital heart disease be detrimental to subsequent pig heart xenotransplantation?

INTRODUCTION

Pig heart xenotransplantation might act as a bridge in infants with complex congenital heart disease (CHD) until a deceased human donor heart becomes available. Infants develop antibodies to wild-type (WT, i.e., genetically-unmodified) pig cells, but rarely to cells in which expression of the 3 known carbohydrate xenoantigens has been deleted by genetic engineering (triple-knockout [TKO] pigs). Our objective was to test sera from children who had undergone palliative surgery for complex CHD (and who potentially might need a pig heart transplant) to determine whether they had serum cytotoxic antibodies against TKO pig cells.

METHODS

Sera were obtained from children with CHD undergoing Glenn or Fontan operation (n = 14) and healthy adults (n = 8, as controls). All of the children had complex CHD and had undergone some form of cardiac surgery. Seven had received human blood transfusions and 3 bovine pericardial patch grafts. IgM and IgG binding to WT and TKO pig red blood cells (RBCs) and peripheral blood mononuclear cells (PBMCs) were measured by flow cytometry, and killing of PBMCs by a complement-dependent cytotoxicity assay.

RESULTS

Almost all children and adults demonstrated relatively high IgM/IgG binding to WT RBCs, but minimal binding to TKO RBCs (p < 0.0001 vs WT), although IgG binding was greater in children than adults (p < 0.01). All sera showed IgM/IgG binding to WT PBMCs, but this was much lower to TKO PBMCs (p < 0.0001 vs WT) and was greater in children than in adults (p < 0.05). Binding to both WT and TKO PBMCs was greater than to RBCs. Mean serum cytotoxicity to WT PBMCs was 90% in both children and adults, whereas to TKO PBMCs it was only 20% and < 5%, respectively. The sera from 6/14 (43%) children were cytotoxic to TKO PBMCs, but no adult sera were cytotoxic.

CONCLUSIONS

Although no children had high levels of antibodies to TKO RBCs, 13/14 demonstrated antibodies to TKO PBMCs, in 6 of these showed mild cytotoxicity. As no adults had cytotoxic antibodies to TKO PBMCs, the higher incidence in children may possibly be associated with their exposure to previous cardiac surgery and biological products. However, the numbers were too small to determine the influence of such past exposures. Before considering pig heart xenotransplantation for children with CHD, testing for antibody binding may be warranted.

Changes in physiological responses and immunity of blunt snout bream Megalobrama amblycephala from transport stress

This study aimed to investigate the effects of transport stress on the physiological responses and immunity of Megalobrama amblycephala (blunt snout bream). Fish (109.67 ± 1.51 g) were sampled at nine time points: before transport (control), at 0 h, 1 h, 3 h, 6 h, 12 h, 24 h, 3 days, and 7 days after 4 h of medium-distance transportation, and four fish were sampled in each time point. The results showed that plasma cortisol, triiodothyronine (T₃), complement component 3 (C3), complement component 4 (C4), immunoglobulin M (IgM) and nitrogen monoxide (NO) concentrations, and alternative complement pathway (ACH50), acid phosphatase (ACP), and myeloperoxidase (MPO) activities all reached the peak at 0 h after transportation; C4 and NO concentrations as well as ACP and MPO activities returned to the control level after 1 h, ACH50 activity as well as cortisol, T_3, and IgM concentration returned to the control level after 12 h, and C3 concentration returned to the control level after 24 h respectively. Plasma glucose and total protein concentrations as well as lysozyme activity all reached the peak at 1 h after transportation, total protein concentration and lysozyme activity returned to the control level after 3 h, and glucose concentration returned to the control level after 6 h (P < 0.05). Liver heat shock protein 70 expression reached the peak at 1 h after transportation, and returned to the control level after 24 h; liver heat shock protein 90 expression reached the peak at 0 h after transportation and returned to the control level after 12 h (P < 0.05). Overall, these findings suggested that 4 h of medium-distance transportation caused stress response of blunt snout bream, and transport stress had a significant effect on plasma indicators. But the recovery of 24 h after transport could return the physiological response, immune indexes, and the expression of heat shock protein to the normal level. This also provided data support for the medium-distance transportation of blunt snout bream in the future.

Toxicity in Takifugu rubripes exposed to acute ammonia: Effects on immune responses, brain neurotransmitter levels, and thyroid endocrine hormones

Exposure to ammonia can cause convulsions, coma, and death. In this study, we investigate the effects of ammonia exposure on immunoregulatory and neuroendocrine changes in Takifugu rubripes. Fish were sampled at 0, 12, 24, 48, and 96 h following exposure to different ammonia concentrations (0, 5, 50, 100, and 150 mg/L). Our results showed that exposure to ammonia significantly reduced the concentrations of C3, C4, IgM, and LZM whereas the heat shock protein 70 and 90 levels significantly increased. In addition, the transcription levels of Mn-SOD, CAT, GRx, and GR in the liver were significantly upregulated following exposure to low ammonia concertation, however, downregulated with increased exposure time. These findings suggest that ammonia poisoning causes oxidative damage and suppresses plasma immunity. Ammonia exposure also resulted in the elevation and depletion of the T3 and T4 levels, respectively. Furthermore, ammonia stress induced an increase in the corticotrophin-releasing hormone, adrenocorticotropic hormone, and cortisol levels, and a decrease in dopamine, noradrenaline, and 5-hydroxytryptamine levels in the brain, illustrating that ammonia poisoning can disrupt the endocrine and neurotransmitter systems. Our results provide insights into the mechanisms underlying the neurotoxic effects of ammonia exposure, which helps to assess the ecological and environmental health risks of this contaminant in marine fish.

Cardiovascular risk factors: The effects of ageing and smoking on the immune system, an observational clinical study

Currently immunomodulatory compounds are under investigation for use in patients with cardiovascular disease, caused by atherosclerosis. These trials, using recurrent cardiovascular events as endpoint, require enrollment of large patient groups. We investigated the effect of key risk factors for atherosclerosis development, ageing and smoking, on the immune system, with the objective to identify biomarkers differentiating between human populations, and potentially serving as endpoints for future phase 1B trials with immunomodulatory compounds. Blood was collected from young healthy volunteers (aged 18-25 years, n=30), young smokers (18-25 years, n=20), elderly healthy volunteers (>60 years, n=20), heavy smokers (>45 years, 15 packyears, n=11) and patients with stable coronary artery disease (CAD) (>60 years, n=27). Circulating immune cell subsets were characterized by flow cytometry, and collected plasma was evaluated by proteomics (Olink). Clear ageing effects were observed, mostly illustrated by a lower level in CD8⁺ and naïve CD4⁺ and CD8⁺ T cells, with an increase in CD4⁺ and CD8⁺ effector memory T cells in elderly healthy volunteers compared to young healthy volunteers. Heavy smokers showed a more inflammatory cellular phenotype, especially a shift in Th1/Th2 ratio: higher Th1 and lower Th2 percentages compared to young healthy volunteers. A significant decrease in circulating atheroprotective oxLDL-specific IgM was found in patients with CAD compared to young healthy volunteers. Elevated pro-inflammatory and chemotactic proteins TREM1 and CCL11 were observed in elderly volunteers compared to young volunteers. In addition, heavy smokers had an increase in pro-inflammatory cytokine IL-6 and lysosomal protein LAMP3. These data show that ageing and smoking are associated with an inflammatory immunophenotype, and that heavy smokers or aged individuals may serve as potential populations for future clinical trials investigating immunomodulatory drugs targeted for cardiovascular disease.

Impacts of tea polyphenols on growth, antioxidant capacity and immunity in juvenile hybrid grouper (Epinephelus fuscoguttatus ♀ × E. lanceolatus ♂) fed high-lipid diets

The experiment aimed to investigate the alteration of tea polyphenols (TP) in growth and immunity for hybrid grouper (Epinephelus fuscoguttatus ♀ × E. lanceolatus ♂) fed high-lipid diets. Six concentrations of TP (0, 0.01, 0.02, 0.04, 0.08, 0.16%, named TP1 (basic diet control), TP2, TP3, TP4, TP5, TP6) were supplied in isonitrogenous (51%) and isolipidic (16.7%) experimental diets. These diets were fed to the juvenile grouper (8.68 ± 0.22 g) for 8 weeks. The results showed that dietary TP significantly increased the weight gain rate and specific growth rate (P < 0.05), compared with the control group. The protein efficiency ratio in TP4 group was significantly higher than that of the control group (P < 0.05). TP supplement in high-lipid diets increased antioxidant capacity in the serum (CAT, GSH-Px, T-AOC) and liver (SOD, CAT, GSH-Px, T-AOC). Additionally, dietary TP decreased oxidative stress (ROS, MDA) and improved immunity (ACP, AKP, LYS, IgM) in the liver. The histology of hepatic tissue indicated that dietary TP alleviated pathological symptoms caused by high-lipid diets. Compared with the control group, appropriate dietary TP significantly up-regulated expression of sod, cat, gsh-px, nrf2, keap1, hsp70, hsp90, myd88, tnfα and down-regulated expression of tlr22, il8, il1β, il10 in the liver (P < 0.05). In the head kidney, expression of myd88, il1β, tnfα and il6 were significantly up-regulated and expression of tlr22 and il10 were significantly down-regulated by dietary TP (P < 0.05). After the challenge of Vibrio harveyi, survival rate in higher doses of TP group (TP4 ∼ TP6) was evidently higher, compared with the control group. In conclusion, TP supplement in high-lipid diets improved antioxidant capacity and enhanced immunity of grouper. We speculate that TP may play the role of an immunostimulant, enhancing immunity and disease resistance by cytokine-medicated immune responses. Based on the second-order regression, 0.092-0.106% tea polyphenols were recommended in juvenile grouper high-lipid diets.

Growth, hemato-biochemical, immune-antioxidant response, and gene expression in Nile tilapia (Oreochromis niloticus) received nano iron oxide-incorporated diets

Nanotechnology has recently played a key role in tackling many aquacultures issues. Hence, the present study targets the evaluation of dietary inclusion of nano iron oxide (nFe₂O₃) on growth performance, hematology, immune-antioxidant responses, ionic regulation and expression of related genes in Nile tilapia (Oreochromis niloticus). Fish were fed supplementary nFe₂O₃ at rates of zero (control), 0.5, and 1 g/kg diet for 30 days. Obtained data demonstrated that nFe₂O₃ significantly (P < 0.05) augmented growth performance (final weight and length, body mass gain, specific growth rate, feed conversion ratio, and length gain rate). Hematological picture {RBCs, Hb, MCV, MCH and MCHC, and leukocytes interpretations (WBCs and monocytes)}; and biochemical indexes including (AST and ALT; total protein; and glucose, and cortisol) were significantly (P < 0.05) improved in nFe₂O₃ supplemented groups. Plasma ionic concentration was also altered with nFe₂O₃ supplementation, and 1g nFe₂O₃ revealed the most marked increase in plasma (Na⁺) potassium (K⁺) levels. Similarly, IgM, nitrous oxide (NO), and lysozyme activity, plus superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx) activities showed a remarkable improvement in 1g nFe₂O₃ group compared to the control. Expression of Insulin-Like Growth Factor-1 (IGF-1) and interleukin 1-β (IL-1β) genes were significantly up-regulated in nFe₂O₃ supplemented groups. Briefly, dietary nFe₂O₃ inclusion had enhanced properties on growth; hemato-biochemical; immune, antioxidative profiles; and related genes expression of O. niloticus, with a recommended concentration of 1g nFe₂O₃.

A Molecular Analysis of Memory B Cell and Antibody Responses Against Plasmodium falciparum Merozoite Surface Protein 1 in Children and Adults From Uganda

Memory B cells (MBCs) and plasma antibodies against Plasmodium falciparum (Pf) merozoite antigens are important components of the protective immune response against malaria. To gain understanding of how responses against Pf develop in these two arms of the humoral immune system, we evaluated MBC and antibody responses against the most abundant merozoite antigen, full-length Pf merozoite surface protein 1 (PfMSP1FL), in individuals from a region in Uganda with high Pf transmission. Our results showed that PfMSP1FL-specific B cells in adults with immunological protection against malaria were predominantly IgG+ classical MBCs, while children with incomplete protection mainly harbored IgM+ PfMSP1FL-specific classical MBCs. In contrast, anti-PfMSP1FL plasma IgM reactivity was minimal in both children and adults. Instead, both groups showed high plasma IgG reactivity against PfMSP1FL, with broadening of the response against non-3D7 strains in adults. The B cell receptors encoded by PfMSP1FL-specific IgG+ MBCs carried high levels of amino acid substitutions and recognized relatively conserved epitopes on the highly variable PfMSP1 protein. Proteomics analysis of PfMSP119-specific IgG in plasma of an adult revealed a limited repertoire of anti-MSP1 antibodies, most of which were IgG1 or IgG3. Similar to B cell receptors of PfMSP1FL-specific MBCs, anti-PfMSP119 IgGs had high levels of amino acid substitutions and their sequences were predominantly found in classical MBCs, not atypical MBCs. Collectively, these results showed evolution of the PfMSP1-specific humoral immune response with cumulative Pf exposure, with a shift from IgM+ to IgG+ B cell memory, diversification of B cells from germline, and stronger recognition of PfMSP1 variants by the plasma IgG repertoire.

MYD88 Mutations: Transforming the Landscape of IgM Monoclonal Gammopathies

The MYD88 gene has a physiological role in the innate immune system. Somatic mutations in MYD88, including the most common L265P, have been associated with the development of certain types of lymphoma. MYD88L265P is present in more than 90% of patients with Waldenström's macroglobulinemia (WM) and IgM monoclonal gammopathy of undetermined significance (IgM-MGUS). The absence of MYD88 mutations in WM patients has been associated with a higher risk of transformation into aggressive lymphoma, resistance to certain therapies (BTK inhibitors), and shorter overall survival. The MyD88 signaling pathway has also been used as a target for specific therapies. In this review, we summarize the clinical applications of MYD88 testing in the diagnosis, prognosis, follow-up, and treatment of patients. Although MYD88L265P is not specific to WM, few tumors present a single causative mutation in a recurrent position. The role of the oncogene in the pathogenesis of WM is still unclear, especially considering that the mutation can be found in normal B cells of patients, as recently reported. This may have important implications for early lymphoma detection in healthy elderly individuals and for the treatment response assessment based on a MYD88L265P analysis.

Co-Expression of the B-Cell Key Transcription Factors Blimp-1 and IRF4 Identifies Plasma Cells in the Pig

Antibody-secreting plasma cells (PCs) have remained largely uncharacterized for years in the field of porcine immunology. For an in-depth study of porcine PCs, we identified cross-reactive antibodies against three key transcription factors: PR domain zinc finger protein-1 (Blimp-1), interferon regulatory factor 4 (IRF4), and paired box 5 (Pax5). A distinct Blimp-1⁺IRF4⁺ cell population was found in cells isolated from blood, spleen, lymph nodes, bone marrow, and lung of healthy pigs. These cells showed a downregulation of Pax5 compared to other B cells. Within Blimp-1⁺IRF4⁺ B cells, IgM-, IgG-, and IgA-expressing cells were identified and immunoglobulin-class distribution was clearly different between the anatomical locations, with IgA⁺ PCs dominating in lung tissue and IgM⁺ PCs dominating in the spleen. Expression patterns of Ki-67, MHC-II, CD9, and CD28 were investigated in the different organs. A high expression of Ki-67 was observed in blood, suggesting a plasmablast stage. Blimp-1⁺IRF4⁺ cells showed an overall lower expression of MHC-II compared to regular B cells, confirming a progressive loss in B-cell differentiation toward the PC stage. CD28 showed slightly elevated expression levels in Blimp-1⁺IRF4⁺ cells in most organs, a phenotype that is also described for PCs in mice and humans. This was not seen for CD9. We further developed a FACS-sorting strategy for live porcine PCs for functional assays. CD3^-CD16^-CD172a^– sorted cells with a CD49d^highFSC-A^high phenotype contained Blimp-1⁺IRF4⁺ cells and were capable of spontaneous IgG production, thus confirming PC identity. These results reveal fundamental phenotypes of porcine PCs and will facilitate the study of this specific B-cell subset in the future.

Effects of dietary protein on water quality, growth performance, RNA/DNA ratio and haemato-immunological indices of soft-shelled turtle (Pelodiscus sinensis)

In aquatic animals, dietary protein plays a crucial role in their growth and immunity. A feeding trial was conducted on soft-shelled turtles (Pelodiscus sinensis) to assess the effects of various levels of protein on the specific growth rate (SGR), ambient water quality (total ammonia nitrogen (TAN), total nitrogen (TN) and total phosphorus (TP)), hematological parameters (respiratory burst (RB), red blood cell count (RBC), albumin content (Alb), hemoglobin level (Hb) and osmolality), plasma immunoglobulin M (IgM) levels and lysozyme activity. Soft-shelled turtles weighing about 4.02 g were fed fish meal-based diets with 14.38%, 20.41%, 26.19%, 32.23%, 37.63% and 45.23% protein for 8 weeks. SGR, RBC, Hb, Alb, RB, IgM and lysozyme activity were enhanced as the dietary protein was increased from 14.38% to 26.19%, then reached a plateau. For identical feeding times, TAN and TN were increased with elevating dietary protein levels. While, no statistically significant differences were observed among the 26.19%, 32.23% and 37.63% groups. When the turtles were cultivated for 56 days and fed with 45.23% protein, the TP in the culturing water was higher than that in the other groups. An increase in dietary protein level up to 26.19% increased the RNA/DNA ratio, which subsequently plateaued at a steady level. The levels of dietary protein had no impact on osmolality or alkaline phosphatase (AKP) activity. On the basis of broken-line analyses derived from SGR, the optimum dietary protein level for soft-shelled turtles was found to be 27.11% protein.

Toxicological damages on copper exposure to IgM+ B cells of Nile tilapia (Oreochromis niloticus) and mitigation of its adverse effects by β-glucan administration

Present investigation was carried out to study toxicological damages of copper exposure and mitigation of its adverse effects with β-glucan administration in IgM⁺ B cells which processes multiple roles similar to macrophages in Nile tilapia (Oreochromis niloticus). IgM⁺ B cells were pretreated with β-glucan (25 μg/mL) for 24 h before exposed to cupric oxide nanoparticles (CuO NPs) or cupric chloride (Cu ions) at the doses of 0, 5, 10, and 20 μg/mL for 24 h, respectively. Our results demonstrated that β-glucan increased reduced glutathione (GSH) to against oxidative damage from CuO NPs and Cu ions exposure in IgM⁺ B cells. The apoptosis process through mitochondrial signaling pathway was depressed in IgM⁺ B cells since the mitochondrial membrane potential (ΔΨm) was protected from copper exposure by β-glucan treatment. Furthermore, the inhibition on phagocytic abilities of IgM⁺ B cells caused by copper exposure could be enhanced with β-glucan treatment via evaluation of microspheres and bioparticles uptake and LPS-induced NO production. Importantly, β-glucan might participate in immunomodulation in IgM⁺ B cells through B cell antigen receptor (BCR) to suppress toxicological effect derived from copper exposure. Taken together, this study provides more information on the toxicological damages in IgM⁺ B cells upon copper exposure and explains the molecular mechanism to reverse adverse effects caused by copper exposure with β-glucan administration.

Pre-COVID-19 Immunity to Common Cold Human Coronaviruses Induces a Recall-Type IgG Response to SARS-CoV-2 Antigens Without Cross-Neutralisation

The capacity of pre-existing immunity to human common coronaviruses (HCoV) to cross-protect against de novo COVID-19is yet unknown. In this work, we studied the sera of 175 COVID-19 patients, 76 healthy donors and 3 intravenous immunoglobulins (IVIG) batches. We found that most COVID-19 patients developed anti-SARS-CoV-2 IgG antibodies before IgM. Moreover, the capacity of their IgGs to react to beta-HCoV, was present in the early sera of most patients before the appearance of anti-SARS-CoV-2 IgG. This implied that a recall-type antibody response was generated. In comparison, the patients that mounted an anti-SARS-COV2 IgM response, prior to IgG responses had lower titres of anti-beta-HCoV IgG antibodies. This indicated that pre-existing immunity to beta-HCoV was conducive to the generation of memory type responses to SARS-COV-2. Finally, we also found that pre-COVID-19-era sera and IVIG cross-reacted with SARS-CoV-2 antigens without neutralising SARS-CoV-2 infectivity in vitro. Put together, these results indicate that whilst pre-existing immunity to HCoV is responsible for recall-type IgG responses to SARS-CoV-2, it does not lead to cross-protection against COVID-19.

Clinical Isolates of Acinetobacter spp. Are Highly Serum Resistant Despite Efficient Recognition by the Complement System

Gram-negative bacteria from the genus Acinetobacter are responsible for life-threating hospital-related infections such as pneumonia, septicemia, and meningitis, especially in immunocompromised patients. Worryingly, Acinetobacter have become multi- and extensively drug resistant (MDR/XDR) over the last few decades. The complement system is the first line of defense against microbes, thus it is highly important to increase our understanding of evasion mechanisms used by Acinetobacter spp. Here, we studied clinical isolates of Acinetobacter spp. (n=50), aiming to characterize their recognition by the complement system. Most isolates tested survived 1 h incubation in 30% serum, and only 8 isolates had a lower survival rate, yet none of those isolates were fully killed. Intriguingly, four isolates survived in human whole blood containing all cell component. Their survival was, however, significantly reduced. Flow cytometry analyses revealed that most of the isolates were detected by human IgG and IgM. Interestingly, we could not detect any significant concentration of deposited C1q, despite observing C4b deposition that was abolished in C1q-deficient serum, indicating transient binding of C1q to bacteria. Moreover, several isolates were recognized by MBL, with C4b deposition abolished in MBL-deficient serum. C3b was deposited on most isolates, but this was not, however, seen with respect to C5b and formation of the membrane attack complex (MAC), indicating that many isolates could avoid complement-mediated lysis. India ink staining showed that isolates were capsulated, and capsule thickness varied significantly between isolates. Studies performed on a wild-type strain and capsule mutant strains, demonstrated that the production of a capsular polysaccharide is one mechanism that mediates resistance to complement-mediated bactericidal activity by preventing MAC deposition and lysis. Our data showed that most clinical Acinetobacter spp. isolates are highly serum resistant despite being efficiently recognized by the complement system.

Scoping review of the applications of peptide microarrays on the fight against human infections

INTRODUCTION

This scoping review explores the use of peptide microarrays in the fight against infectious diseases. The research domains explored included the use of peptide microarrays in the mapping of linear B-cell and T cell epitopes, antimicrobial peptide discovery, immunosignature characterisation and disease immunodiagnostics. This review also provides a short overview of peptide microarray synthesis.

METHODS

Electronic databases were systematically searched to identify relevant studies. The review was conducted using the Joanna Briggs Institute methodology for scoping reviews and data charting was performed using a predefined form. The results were reported by narrative synthesis in line with the Preferred Reporting Items for Systematic reviews and Meta-Analyses extension for Scoping Reviews guidelines.

RESULTS

Ninety-five articles from 103 studies were included in the final data charting process. The majority (92. 0%) of the articles were published during 2010-2020 and were mostly from Europe (44.2%) and North America (34.7%). The findings were from the investigation of viral (45.6%), bacterial (32. 0%), parasitic (23.3%) and fungal (2. 0%) infections. Out of the serological studies, IgG was the most reported antibody type followed by IgM. The largest portion of the studies (77.7%) were related to mapping B-cell linear epitopes, 5.8% were on diagnostics, 5.8% reported on immunosignature characterisation and 8.7% reported on viral and bacterial cell binding assays. Two studies reported on T-cell epitope profiling.

CONCLUSION

The most important application of peptide microarrays was found to be B-cell epitope mapping or antibody profiling to identify diagnostic and vaccine targets. Immunosignatures identified by random peptide microarrays were found to be applied in the diagnosis of infections and interrogation of vaccine responses. The analysis of the interactions of random peptide microarrays with bacterial and viral cells using binding assays enabled the identification of antimicrobial peptides. Peptide microarray arrays were also used for T-cell linear epitope mapping which may provide more information for the design of peptide-based vaccines and for the development of diagnostic reagents.

Loss of Id3 (Inhibitor of Differentiation 3) Increases the Number of IgM-Producing B-1b Cells in Ischemic Skeletal Muscle Impairing Blood Flow Recovery During Hindlimb Ischemia

OBJECTIVE

Neovascularization can maintain and even improve tissue perfusion in the setting of limb ischemia during peripheral artery disease. The molecular and cellular mechanisms mediating this process are incompletely understood. We investigate the potential role(s) for Id3 (inhibitor of differentiation 3) in regulating blood flow in a murine model of hindlimb ischemia (HLI). Approach and Results: HLI was modeled through femoral artery ligation and resection and blood flow recovery was quantified by laser Doppler perfusion imaging. Mice with global Id3 deletion had significantly impaired perfusion recovery at 14 and 21 days of HLI. Endothelial- or myeloid cell-specific deletion of Id3 revealed no effect on perfusion recovery while B-cell-specific knockout of Id3 (Id3BKO) revealed a significant attenuation of perfusion recovery. Flow cytometry revealed no differences in ischemia-induced T cells or myeloid cell numbers at 7 days of HLI, yet there was a significant increase in B-1b cells in Id3BKO. Consistent with these findings, ELISA (enzyme-linked immunoassay) demonstrated increases in skeletal muscle and plasma IgM. In vitro experiments demonstrated reduced proliferation and increased cell death when endothelial cells were treated with conditioned media from IgM-producing B-1b cells and tibialis anterior muscles in Id3BKO mice showed reduced density of total CD31+ and αSMA+CD31+ vessels.

CONCLUSIONS

This study is the first to demonstrate a role for B-cell-specific Id3 in maintaining blood flow recovery during HLI. Results suggest a role for Id3 in promoting blood flow during HLI and limiting IgM-expressing B-1b cell expansion. These findings present new mechanisms to investigate in peripheral artery disease pathogenesis.

Clinical relevance of glomerular IgM deposition in patients with lupus nephritis

BACKGROUND

The aim of the study was to investigate the clinical relevance of IgM deposition in patients with lupus nephritis (LN) in a large cohort.

RESULTS

217 patients with renal biopsy-proven active LN were enrolled. The associations between glomerular IgM deposition and clinicopathological parameters were further analyzed. IgM deposition was positively correlated with glomerular C1q and C3 deposition moderately (r = 0.436, P < 0.001; r = 0.408, P < 0.001, respectively), and inversely correlated with plasma levels of C3 and CFH mildly (r =  - 0.138, P = 0.043; r =  - 0.147, P = 0.037, respectively). By multivariate analysis, we found that glomerular IgM deposition independently contributed to glomerular C3 deposition in patients with LN (OR = 2.002, 95% CI 1.295-3.094, P = 0.002). In addition, we also found that patients with IgM 0-2+ had similar plasma CFH levels, but in patients with IgM3+-4+, plasma CFH levels were significantly lower (300.4 ± 155.8 μg/mL vs. 429.9 ± 187.5 μg/mL, P < 0.001). Furthermore, patients with high density of glomerular IgM and low levels of CFH had heavier proteinuria, higher serum creatinine and lower plasma C3 levels (5.7 ± 3.1 g/d vs. 4.7 ± 3.5 g/d, P = 0.037; 150.1 ± 121.0 μmol/L vs. 105.6 ± 97.1 μmol/L, P = 0.005; 0.3 ± 0.2 μg/L vs. 0.4 ± 0.2 μg/L, P = 0.04, respectively), comparing with those with low density of glomerular IgM and low levels of CFH.

CONCLUSIONS

Our results suggested the involvement of glomerular deposited IgM in complement activation and renal injury in LN.

B Cell Receptor Repertoire Analysis in Malaria-Naive and Malaria-Experienced Individuals Reveals Unique Characteristics of Atypical Memory B Cells

Malaria, caused by parasites of the Plasmodium genus, is responsible for significant morbidity and mortality globally. Chronic Plasmodium falciparum exposure affects the B cell compartment, leading to the accumulation of atypical memory B cells (atMBCs). IgM-positive (IgM+) and IgG+ atMBCs have not been compared in-depth in the context of malaria, nor is it known if atMBCs in malaria-experienced individuals are different from phenotypically similar B cells in individuals with no known history of Plasmodium exposure. To address these questions, we characterized the B cell receptor (BCR) repertoire of naive B cells (NBCs), IgM+ and IgG+ classical MBCs (cMBCs), and IgM+ and IgG+ atMBCs from 13 malaria-naive American adults and 7 malaria-experienced Ugandan adults. Our results demonstrate that P. falciparum exposure mainly drives changes in atMBCs. In comparison to malaria-naive adults, the BCR repertoire of Plasmodium-exposed adults showed increased levels of somatic hypermutation in the heavy chain V region in IgM+ and IgG+ atMBCs, shorter heavy chain complementarity-determining region 3 (HCDR3) in IgG+ atMBCs, and increased usage of IGHV3-73 in IgG+ cMBCs and both IgM+ and IgG+ atMBCs. Irrespective of Plasmodium exposure, IgM+ atMBCs closely resembled NBCs, while IgG+ atMBCs resembled IgG+ cMBCs. Physicochemical properties of the HCDR3 seemed to be intrinsic to cell type and independent of malaria experience. The resemblance between atMBCs from Plasmodium-exposed and naive adults suggests similar differentiation pathways regardless of chronic antigen exposure. Moreover, these data demonstrate that IgM+ and IgG+ atMBCs are distinct populations that should be considered separately in future analyses. IMPORTANCE Malaria, caused by Plasmodium parasites, still contributes to a high global burden of disease, mainly in children under 5 years of age. Chronic and recurrent Plasmodium infections affect the development of B cell memory against the parasite and promote the accumulation of atypical memory B cells (atMBCs), which have an unclear function in the immune response. Understanding where these cells originate from and whether they are beneficial in the immune response to Plasmodium will help inform vaccination development efforts. We found differences in B cell receptor (BCR) properties of atMBCs between malaria-naive and malaria-experienced adults that are suggestive of divergent selection processes, resulting in more somatic hypermutation and differential immunoglobulin heavy chain V (IGHV) gene usage. Despite these differences, atMBCs from malaria-naive and malaria-experienced adults also showed many similarities in BCR characteristics, such as physicochemical properties of the HCDR3 region, suggesting that atMBCs undergo similar differentiation pathways in response to different pathogens. Our study provides new insights into the effects of malaria experience on the B cell compartment and the relationships between atMBCs and other B cell populations.

The importance of the Atlantic salmon peritoneal cavity B cell response: Local IgM secreting cells are predominant upon Piscirickettsia salmonis infection

The intraperitoneal route is favored for administration of inactivated and attenuated vaccines in Atlantic salmon. Nevertheless, the immune responses in the teleost peritoneal cavity (PerC) are still incompletely defined. In this study, we investigated the B cell responses after intraperitoneal Piscirickettsia salmonis (P. salmonis) challenge of Atlantic salmon, focusing on the local PerC response versus responses in the lymphatic organs: spleen and head kidney. We observed a major increase of leukocytes, total IgM antibody secreting cells (ASC), and P. salmonis-specific ASC in the PerC at 3- and 6-weeks post infection (wpi). The increase in ASC frequency was more prominent in the spleen and PerC compared to the head kidney during the observed 6 wpi. The serum antibody response included P. salmonis-specific antibodies and non-specific antibodies recognizing the non-related bacterial pathogen Yersinia ruckeri and the model antigen TNP-KLH. Finally, we present evidence that supports a putative role for the adipose tissue in the PerC immune response.

Critical role of IL-25-ILC2-IL-5 axis in the production of anti-Francisella LPS IgM by B1 B cells

B1 cells, a subset of B lymphocytes whose developmental origin, phenotype, and function differ from that of conventional B2 cells, are the main source of “natural” IgM but can also respond to infection by rapidly producing pathogen-specific IgM directed against T-independent antigens. Francisella tularensis (Ft) is a Gram-negative bacterium that causes tularemia. Infection with Ft Live Vaccine Strain activates B1 cells for production of IgM directed against the bacterial LPS in a process incompletely understood. Here we show that immunization with purified Ft LPS elicits production of LPS-specific IgM and IgG₃ by B1 cells independently of TLR2 or MyD88. Immunization, but not infection, generated peritoneum-resident memory B1 cells that differentiated into LPS-specific antibody secreting cells (ASC) upon secondary challenge. IL-5 was rapidly induced by immunization with Ft LPS and was required for production of LPS-specific IgM. Antibody-mediated depletion of ILC2 indicated that these cells were the source of IL-5 and were required for IgM production. IL-25, an alarmin that strongly activates ILC2, was rapidly secreted in response to immunization or infection and its administration to mice significantly increased IgM production and B1 cell differentiation to ASC. Conversely, mice lacking IL-17RB, the IL-25 receptor, showed impaired IL-5 induction, IgM production, and B1 ASC differentiation in response to immunization. Administration of IL-5 to Il17rb^-/- mice rescued these B1 cells-mediated responses. Il17rb^-/- mice were more susceptible to infection with Ft LVS and failed to develop immunity upon secondary challenge suggesting that LPS-specific IgM is one of the protective adaptive immune mechanisms against tularemia. Our results indicated that immunization with Ft LPS triggers production of IL-25 that, through stimulation of IL-5 release by ILC2, promotes B1 cells activation and differentiation into IgM secreting cells. By revealing the existence of an IL-25-ILC2-IL-5 axis our results suggest novel strategies to improve vaccination against T-independent bacterial antigens.

B1 cells are a subset of B lymphocytes that participate in the immune response to infection by producing antibodies of the IgM class. Here we investigate the mechanisms that control B1 cells activation and production of IgM directed against the lipopolysaccharide (LPS) of Francisella tularensis, a Gram-negative bacterium that causes tularemia. Using a mouse model of tularemia, our results revealed that Francisella LPS elicits production of the cytokine IL-25 that in turn activates blood cells called Innate Lymphoid Cells 2 (ILC2). Once activated, ILC2 produce the cytokine IL-5 that is required for activation of B1 cells and production of IgM. Mice unresponsive to IL-25 are more susceptible to F. tularensis infection. By revealing the existence of an IL-25-ILC2-IL-5 axis our results suggest novel strategies to improve vaccination against bacteria.

Temporal Dynamics of T Helper Populations in the Proximal Small Intestine after Oral Bovine Lactoferrin Administration in BALB/c Mice

Bovine lactoferrin (bLf), a component of milk and a dietary supplement, modulates intestinal immunity at effector and inductor sites. Considering the regional difference in intestinal compartments and the dynamics of local cytokine-producing cells in the gut across time, the aim of this work was to characterize the effects of bLf on the proximal small intestine in a BALB/c murine model of oral administration. Male BALB/c mice were treated with oral bLf vs. saline control as mock by buccal deposition for 28 days. Intestinal secretions were obtained at different time points and cells were isolated from Peyer's patches (PP) and lamina propria (LP) of the proximal small intestine as representative inductor and effector sites, respectively. Total and specific anti-bLF IgA and IgM were determined by enzyme-immuno assay; the percentages of IgA+ and IgM+ plasma cells (PC) and cytokine-producing CD4+ T cells of PP and LP were analyzed by flow cytometry. We found that total and bLf-specific IgA and IgM levels were increased in the intestinal secretions of the bLf group in comparison to mock group and day 0. LP IgA+ PC and IgM+ PC presented an initial elevation on day 7 and day 21, respectively, followed by a decrease on day 28 in comparison to mock. Higher percentages of CD4+ T cells in LP were found in the bLf group. Cytokines-producing CD4+ T cells populations presented a pattern of increases and decreases in the bLf group in both LP and PP. Transforming growth factor beta (TGF-β)+ CD4+ T cells showed higher percentages after bLf administration with a marked peak at day 21 in both LP and PP in comparison to mock-treated mice. Oral bLf exhibits complex immune properties in the proximal small intestine, where temporal monitoring of the inductor and effector compartments reveals patterns of rises and falls of different cell populations. Exceptionally, TGF-β+ CD4+ T cells show consistent higher numbers after bLf intervention across time. Our work suggests that isolated measurements do not show the complete picture of the modulatory effects of oral bLf in immunological sites as dynamic as the proximal small intestine.

Differences between Human and Mouse IgM Fc Receptor (FcµR)

Both non-immune "natural" and antigen-induced "immune" IgM are important for protection against pathogens and for regulation of immune responses to self-antigens. Since the bona fide IgM Fc receptor (FcµR) was identified in humans by a functional cloning strategy in 2009, the roles of FcµR in these IgM effector functions have begun to be explored. In this short essay, we describe the differences between human and mouse FcµRs in terms of their identification processes, cellular distributions and ligand binding activities with emphasis on our recent findings from the mutational analysis of human FcµR. We have identified at least three sites of human FcµR, i.e., Asn66 in the CDR2, Lys79 to Arg83 in the DE loop and Asn109 in the CDR3, responsible for its constitutive IgM-ligand binding. Results of computational structural modeling analysis are consistent with these mutational data and a model of the ligand binding, Ig-like domain of human FcµR is proposed. Serendipitously, substitution of Glu41 and Met42 in the CDR1 of human FcµR with mouse equivalents Gln and Leu, either single or more prominently in combination, enhances both the receptor expression and IgM binding. These findings would help in the future development of preventive and therapeutic interventions targeting FcµR.