Defining Natural Antibodies

Clones reactive to apoptotic cells and specific chemical adducts are prevalent among human thymic B cells

Introduction

Thymus resident B cells were described more than 40 years ago. In early human life, these cells are found predominantly in the medulla and overwhelmingly display an unswitched IgM+ phenotype. The reactivity of thymic IgM B cells, however, is still unclear.

Methods

Here, we generated 120 IgM-producing B cell clones from 3 separate thymus specimens obtained from infant, adolescent, and adult donors. Using flow cytometry and a unique high-dimensional ELISA platform, we investigated the clones' reactivity to apoptotic cells as well as to common chemical adducts exposed on modified amino acids and other macromolecules.

Results

Regardless of the age, approximately 30-40% of thymic IgM B cells reacted to apoptotic cells. Further, 30-40% displayed reactivity to at least one adduct, including malondialdehyde, Homocysteine, and NEDD 8. Four distinct reactivity patterns were identified through this profiling. Notably, a significant association was observed between reactivity to apoptotic cells, and to one or more adducts, suggesting that the same determinants were recognized in both assays. Additionally, thymic IgM B cells reactive to adducts were more likely to recognize intra-nuclear or intra-cytoplasmic structures in Hep-2 cells as revealed by immunofluorescence staining.

Conclusion/Discussion

Collectively, our findings suggest that thymic IgM B cells actively uptake apoptotic bodies and cellular debris in the medulla by binding specific chemical adducts. This mechanism could underpin their antigen-presenting function and further support their role in T-cell negative selection.

Comparative Efficacy of Parenteral and Mucosal Recombinant Probiotic Vaccines Against SARS-CoV-2 and S. pneumoniae Infections in Animal Models

BACKGROUND

The accumulation of specific IgG antibodies in blood serum is considered a key criterion for the effectiveness of vaccination. For several vaccine-preventable infections, quantitative indicators of the humoral response have been established, which, when reached, provide a high probability of protection against infection. The presence of such a formal correlate of vaccine effectiveness is crucial, for example, in organizing preventive measures and validating newly developed vaccines. However, can effective protection against infection occur when the level of serum antibodies is lower than that provided by parenteral vaccination? Will protection be sufficient if the same vaccine antigen is administered via mucosal membranes without achieving high levels of specific IgG circulating in the blood?

METHODS

In this study, we compared the immunogenicity and protective efficacy of parenteral and mucosal forms of vaccines in experimental animals, targeting infections caused by the SARS-CoV-2 coronavirus and Streptococcus pneumoniae. We investigated the protective properties of a fragment of the coronavirus S1 protein administered intramuscularly with an adjuvant and orally as part of the probiotic strain Enterococcus faecium L3 in a Syrian hamster model. A comparative assessment of the immunogenicity and protective efficacy of a recombinant tandem (PSP) of immunogenic peptides from S. pneumoniae surface proteins, administered either parenterally or orally, was performed in a Balb/c mouse model.

RESULTS

Both models demonstrated significant differences in the immunogenicity of parenteral and oral vaccine antigens, but comparable protective efficacy.

O-glycosylation of IgA1 and the pathogenesis of an autoimmune disease IgA nephropathy

IgA nephropathy is a kidney disease characterized by deposition of immune complexes containing abnormally O-glycosylated IgA1 in the glomeruli. Specifically, some O-glycans are missing galactose that is normally β1,3-linked to N-acetylgalactosamine of the core 1 glycans. These galactose-deficient IgA1 glycoforms are produced by IgA1-secreting cells due to a dysregulated expression and activity of several glycosyltransferases. Galactose-deficient IgA1 in the circulation of patients with IgA nephropathy is bound by IgG autoantibodies and the resultant immune complexes can contain additional proteins, such as complement C3. These complexes, if not removed from the circulation, can enter the glomerular mesangium, activate the resident mesangial cells, and induce glomerular injury. In this review, we briefly summarize clinical and pathological features of IgA nephropathy, review normal and aberrant IgA1 O-glycosylation pathways, and discuss the origins and potential significance of natural anti-glycan antibodies, namely those recognizing N-acetylgalactosamine. We also discuss the features of autoantibodies specific for galactose-deficient IgA1 and the characteristics of pathogenic immune complexes containing IgA1 and IgG. In IgA nephropathy, kidneys are injured by IgA1-containing immune complexes as innocent bystanders. Most patients with IgA nephropathy progress to kidney failure and require dialysis or transplantation. Moreover, most patients after transplantation experience a recurrent disease. Thus, a better understanding of the pathogenetic mechanisms is needed to develop new disease-specific treatments.

Levels of Natural Antibodies Before and After Immunoglobulin Replacement Treatment Affect the Clinical Phenotype in Common Variable Immunodeficiency

Natural antibodies (NAbs) occurring in individuals without prior exposure to specific antigens, provide direct first barrier protection against pathogens, and exert immunoregulation thus actively contributing to the maintenance of immune homeostasis, controlling inflammatory processes and preventing autoimmunity. Common variable immunodeficiency (CVID) is a heterogeneous group of disorders characterized by a compromised immune function that brings into focus the role of NAbs. Our aim was to explore whether NAb levels could serve as potential key indicators in CVID for monitoring disease progression and predicting outcomes. In this study, we analyzed a Hellenic cohort of 56 patients with CVID (31 newly diagnosed and 25 under immunoglobulin replacement therapy-IgRT) and 33 healthy controls, for total Ig levels and serum IgM and IgG NAb levels against five informative target-antigens of NAbs, namely, actin, DNA, carbonic anhydrase, F(ab΄)2 fragments of human IgG and TriNitroPhenyl. In addition, follow-up pre- and post- IgRT samples were analyzed in ten (10) patients of our cohort. Results showed that Ig-treated patients exhibited significantly lower IgM NAb levels than untreated patients and healthy controls against all panel antigens. In the follow-up samples, pre-treatment IgM NAb levels negatively correlated with total serum IgM. This imbalance was only partially restored after IgRT, with a significant decrease in IgM NAb levels observed in nine out of ten patients. Moreover, post-treatment patients with recurrent infections presented significantly lower IgM NAb levels, a reduction also observed in patients with bronchiectasis independently of treatment status. On the contrary, post-treatment patients with enteropathy had significantly higher IgM NAb levels against all panel antigens, an increase also noted in patients with autoimmune diseases. Regarding IgG NAbs, replacement therapy restored levels to those of healthy controls. In conclusion, impaired NAb levels are found in CVID patients, particularly related to certain phenotypes. Moreover, the significant decrease in IgM NAb levels after IgRT suggests a potential association with disease course and complications. The results suggest that administration of human IgM NAbs may be an effective combinatorial treatment in selected patients. Further research is needed to understand the functional roles of NAbs in CVID and its complex clinical phenotypes.

Antigen specificity affects analysis of natural antibodies

Natural antibodies are used to compare immune systems across taxa, to study wildlife disease ecology, and as selection markers in livestock breeding. These immunoglobulins are present prior to immune stimulation. They are described as having low antigen specificity or polyreactive binding and are measured by binding to self-antigens or novel exogenous proteins. Most studies use only one or two antigens to measure natural antibodies and ignore potential effects of antigen specificity in analyses. It remains unclear how different antigen-specific natural antibodies are related or how diversity among natural antibodies may affect analyses of these immunoglobulins. Using genetically distinct lines of chickens as a model system, we tested the hypotheses that (1) antigen-specific natural antibodies are independent of each other and (2) antigen specificity affects the comparison of natural antibodies among animals. We used blood cell agglutination and enzyme-linked immunosorbent assays to measure levels of natural antibodies binding to four antigens: (i) rabbit erythrocytes, (ii) keyhole limpet hemocyanin, (iii) phytohemagglutinin, or (iv) ovalbumin. We observed that levels of antigen specific natural antibodies were not correlated. There were significant differences in levels of natural antibodies among lines of chickens, indicating genetic variation for natural antibody production. However, line distinctions were not consistent among antigen specific natural antibodies. These data show that natural antibodies are a pool of relatively distinct immunoglobulins, and that antigen specificity may affect interpretation of natural antibody function and comparative immunology.

Microbiota and B-1 B cell repertoire development in mice

Microbiota-derived antigens play a critical role in the development of both the mucosal and systemic B cell repertoires; however, how glycan epitopes promote B cell repertoire selection is only recently being understood. The production of glycan-derived antigens by individual microbes within a host can be dynamic and influenced by interactions within other members of microbial communities, the composition of diet, and host-derived contents, including those of the mucosal immune system. The size and complexity of the emerging neonatal B cell repertoire are paralleled by the acquisition of a diverse microbiota from maternal and environmental sources, which is now appreciated to exert long-lasting influences on the nascent B cell repertoire.

Understanding the Specific Implications of Amino Acids in the Antibody Development

As the demand for immunotherapy to treat and manage cancers, infectious diseases and other disorders grows, a comprehensive understanding of amino acids and their intricate role in antibody engineering has become a prime requirement. Naturally produced antibodies may not have the most suitable amino acids at the complementarity determining regions (CDR) and framework regions, for therapeutic purposes. Therefore, to enhance the binding affinity and therapeutic properties of an antibody, the specific impact of certain amino acids on the antibody's architecture must be thoroughly studied. In antibody engineering, it is crucial to identify the key amino acid residues that significantly contribute to improving antibody properties. Therapeutic antibodies with higher binding affinity and improved functionality can be achieved through modifications or substitutions with highly suitable amino acid residues. Here, we have indicated the frequency of amino acids and their association with the binding free energy in CDRs. The review also analyzes the experimental outcome of two studies that reveal the frequency of amino acids in CDRs and provides their significant correlation between the outcomes. Additionally, it discusses the various bond interactions within the antibody structure and antigen binding. A detailed understanding of these amino acid properties should assist in the analysis of antibody sequences and structures needed for designing and enhancing the overall performance of therapeutic antibodies.

Genetic Variation in Natural and Induced Antibody Responses in Layer Chickens

Selection of livestock for disease resistance is challenging due to the difficulty in obtaining reliable phenotypes. Antibodies are immunological molecules that provide direct and indirect defenses against infection and link the activities of both the innate and adaptive compartments of the immune system. As a result, antibodies have been used as a trait in selection for immune defense. The goal of this study was to identify genomic regions associated with natural and induced antibodies in chickens using low-pass sequencing. Enzyme-linked immunosorbent assays were used to quantify innate (natural) antibodies binding KLH, OVA, and PHA and induced (adaptive) antibodies binding IBD, IBV, NDV, and REO. We collected plasma from four White Leghorn (WL), two White Plymouth Rock (WPR), and two Rhode Island Red (RIR) lines. Samples numbers ranged between 198 and 785 per breed. GWAS was performed within breed on data pre-adjusted for Line-Hatch-Sex effects using GCTA. A threshold of p = 10-6 was used to select genes for downstream annotation and enrichment analysis with SNPEff and Panther. Significant enrichment was found for the defense/immunity protein, immunoglobulin receptor superfamily, and the antimicrobial response protein in RIR; and the immunoglobulin receptor superfamily, defense/immunity protein, and protein modifying enzyme in WL. However, none were present in WPR, but some of the selected SNP were annotated in immune pathways. This study provides new insights regarding the genetics of the antibody response in layer chickens.

Natural IgG protects against early dissemination of vesicular stomatitis virus

Neonatal Fc receptor (FcRn) recycles immunoglobulin G, and inhibition of FcRn is used clinically for treatment of autoimmune diseases. In this work, using the vesicular stomatitis virus (VSV) mouse infection model system, we determined the role of FcRn during virus infection. While induction of neutralizing antibodies and long-term protection of these antibodies was hardly affected in FcRn deficient mice, FcRn deficiency limited the amount of natural IgG (VSV-specific) antibodies. Lack of natural antibodies (nAbs) limited early control of VSV in macrophages, accelerated propagation of virus in several organs, led to the spread of VSV to the neural tissue resulting in fatal outcomes. Adoptive transfer of natural IgG into FcRn deficient mice limited early propagation of VSV in FcRn deficient mice and enhanced survival of FcRn knockout mice. In line with this, vaccination of FcRn mice with very low dose of VSV prior to infection similarly prevented death after infection. In conclusion we determined the importance of nAbs during VSV infection. Lack of FcRn limited nAbs and thereby enhanced the susceptibility to virus infection.

Clinical Significance of Uncommon, Non-Clinical, and Novel Autoantibodies

Autoantibodies are a common mark of autoimmune reaction and their identification in the patients' serum, cerebrospinal fluid, or tissues is generally believed to represent diagnostic or prognostic biomarkers of autoimmune diseases or autoinflammatory conditions. Traditionally, autoantibody testing is an important part of the clinical examination of suspected patients, and in the absence of reliable T cell tests, characterization of autoantibody responses might be suitable in finding causes of specific autoimmune responses, their strength, and sometimes commencement of autoimmune disease. Autoantibodies are also useful for prognostic stratification in clinically diverse groups of patients if checked repeatedly. Antibody discoveries are continuing, with important consequences for verifying autoimmune mechanisms, diagnostic feasibility, and clinical management. Adding newly identified autoantibody-autoantigen pairs to common clinical laboratory panels should help upgrade and harmonize the identification of systemic autoimmune rheumatic disorders and other autoimmune conditions. Herein, we aim to summarize our current knowledge of uncommon and novel autoantibodies in the context of discussing their validation, diagnostic practicability, and clinical relevance. The regular updates within the field are important and well justified.

The role of B-1 cells in cancer progression and anti-tumor immunity

In recent years, in addition to the well-established role of T cells in controlling or promoting tumor growth, a new wave of research has demonstrated the active involvement of B cells in tumor immunity. B-cell subsets with distinct phenotypes and functions play various roles in tumor progression. Plasma cells and activated B cells have been linked to improved clinical outcomes in several types of cancer, whereas regulatory B cells have been associated with disease progression. However, we are only beginning to understand the role of a particular innate subset of B cells, referred to as B-1 cells, in cancer. Here, we summarize the characteristics of B-1 cells and review their ability to infiltrate tumors. We also describe the potential mechanisms through which B-1 cells suppress anti-tumor immune responses and promote tumor progression. Additionally, we highlight recent studies on the protective anti-tumor function of B-1 cells in both mouse models and humans. Understanding the functions of B-1 cells in tumor immunity could pave the way for designing more effective cancer immunotherapies.

Prevalence of a large panel of systemic autoantibodies in the Bavarian adult population

Objective

Autoimmune diseases commonly feature the presence of specific humoral autoantibodies. However, the prevalence of a large panel of systemic autoantibodies has never been assessed in the general population. We, therefore, described the prevalence of about 50 humoral systemic autoantibodies in a sample of the general Bavarian adult population.

Methods

Non-fasting venous serum samples from 331 participants were analyzed for 7 autoantibody screening tests (nuclear, cytoplasmic, and mitotic ANA, ANCA, cANCA and pANCA, anti-ENA autoantibodies) and 44 different monospecific humoral non-organ specific/systemic autoantibodies using indirect immunofluorescence tests, ELISAs, and line blots. In order to assess associations between sex, age, BMI, education level, smoking status and the presence of systemic autoantibodies, logistic regression analyses were conducted.

Results

At least one screening test was positive in 29.9% of the participants, and 42.3% of the participants were seropositive for at least one monospecific autoantibody. The most frequently found monospecific autoantibodies were rheumatoid factor (35.6%), ß2-glycoprotein 1 IgM (4.8%), and cardiolipin IgG (1.8%). Only few associations between sex, age, BMI, education, smoking status and autoantibody frequencies were observed.

Conclusion

Systemic autoantibodies are common in the general Bavarian population, and largely independent of sex, age, BMI, education, or smoking status. The study results may give orientation to clinicians about the occurrence of autoantibodies in the population, not (yet) associated with clinical symptoms.

Influence of pre-B cell receptor deficiency on the immunoglobulin repertoires in peripheral blood B cells before and after immunization

During B cell development, pre-B cell receptor (pre-BCR), comprising the immunoglobulin heavy chain (HC) and surrogate light chain (SLC), plays a crucial role. The expression of pre-BCR serves as a certification of HC quality, confirming its ability to associate with the SLC and light chain (LC). In mice lacking SLC, the absence of this quality control mechanism leads to a distorted repertoire of HCs in the spleen and bone marrow. In this study, we conducted a comparative analysis of the immunoglobulin gene repertoire in peripheral blood cells of both wild-type mice and pre-BCR-deficient mice. Our findings reveal differences not only in the μ HC repertoire but also in the α HC and κ LC repertoires of the pre-BCR-deficient mice. These results suggest that the pre-BCR-mediated quality check of HC influences the selection of class-switched HC and LC repertoires. To further explore the impact of pre-BCR deficiency, we immunized these mice with thymus-dependent antigens and compared the antigen-responding repertoires. Our observations indicate that the affinity maturation pathways remain consistent between wild-type mice and pre-BCR-deficient mice, albeit with variations in the degree of maturation.

Sex, T Cells, and the Microbiome in Natural ABO Antibody Production in Mice

BACKGROUND

"Natural" ABO antibodies (Abs) are produced without known exposure to A/B carbohydrate antigens, posing significant risks for hyperacute rejection during ABO-incompatible transplantation. We investigated anti-A "natural" ABO antibodies versus intentionally induced Abs with regard to the need for T-cell help, the impact of sex, and stimulation by the microbiome.

METHODS

Anti-A was measured by hemagglutination assay of sera from untreated C57BL/6 wild-type (WT) or T cell-deficient mice of both sexes. Human ABO-A reagent blood cell membranes were injected intraperitoneally to induce anti-A Abs. The gut microbiome was eliminated by maintenance of mice in germ-free housing.

RESULTS

Compared with WT mice, CD4 + T-cell knockout (KO), major histocompability complex-II KO, and αβ/γδ T-cell receptor KO mice produced much higher levels of anti-A nAbs; females produced dramatically more anti-A nAbs than males, rising substantially with puberty. Sensitization with human ABO-A reagent blood cell membranes did not induce additional anti-A in KO mice, unlike WT. Sex-matched CD4 + T-cell transfer significantly suppressed anti-A nAbs in KO mice and rendered mice responsive to A-sensitization. Even under germ-free conditions, WT mice of several strains produced anti-A nAbs, with significantly higher anti-A nAbs levels in females than males.

CONCLUSIONS

Anti-A nAbs were produced without T-cell help, without microbiome stimulation, in a sex- and age-dependent manner, suggestive of a role for sex hormones in regulating anti-A nAbs. Although CD4 + T cells were not required for anti-A nAbs, our findings indicate that T cells regulate anti-A nAb production. In contrast to anti-A nAbs, induced anti-A production was T-cell dependent without a sex bias.

Hapten/Myristoyl Functionalized Poly(propyleneimine) Dendrimers as Potent Cell Surface Recruiters of Antibodies for Mediating Innate Immune Killing

Recruiting endogenous antibodies to the surface of cancer cells using antibody-recruiting molecules has the potential to unleash innate immune effector killing mechanisms against antibody-bound cancer cells. The affinity of endogenous antibodies is relatively low, and many currently explored antibody-recruiting strategies rely on targeting over-expressed receptors, which have not yet been identified in most solid tumors. Here, both challenges are addressed by functionalizing poly(propyleneimine) (PPI) dendrimers with both multiple dinitrophenyl (DNP) motifs, as anti-hapten antibody-recruiting motifs, and myristoyl motifs, as universal phospholipid cell membrane anchoring motifs, to recruit anti-hapten antibodies to cell surfaces. By exploiting the multivalency of the ligand exposure on the dendrimer scaffold, it is demonstrated that dendrimers featuring ten myristoyl and six DNP motifs exhibit the highest antibody-recruiting capacity in vitro. Furthermore, it is shown that treating cancer cells with these dendrimers in vitro marks them for phagocytosis by macrophages in the presence of anti-hapten antibodies. As a proof-of-concept, it is shown that intratumoral injection of these dendrimers in vivo in tumor-bearing mice results in the recruitment of anti-DNP antibodies to the cell surface in the tumor microenvironment. These findings highlight the potential of dendrimers as a promising class of novel antibody-recruiting molecules for use in cancer immunotherapy.

Mechanisms of Formation of Antibodies against Blood Group Antigens That Do Not Exist in the Body

The system of the four different human blood groups is based on the oligosaccharide antigens A or B, which are located on the surface of blood cells and other cells including endothelial cells, attached to the membrane proteins or lipids. After transfusion, the presence of these antigens on the apical surface of endothelial cells could induce an immunological reaction against the host. The final oligosaccharide sequence of AgA consists of Gal-GlcNAc-Gal (GalNAc)-Fuc. AgB contains Gal-GlcNAc-Gal (Gal)-Fuc. These antigens are synthesised in the Golgi complex (GC) using unique Golgi glycosylation enzymes (GGEs). People with AgA also synthesise antibodies against AgB (group A [II]). People with AgB synthesise antibodies against AgA (group B [III]). People expressing AgA together with AgB (group AB [IV]) do not have these antibodies, while people who do not express these antigens (group O [0; I]) synthesise antibodies against both antigens. Consequently, the antibodies are synthesised against antigens that apparently do not exist in the body. Here, we compared the prediction power of the main hypotheses explaining the formation of these antibodies, namely, the concept of natural antibodies, the gut bacteria-derived antibody hypothesis, and the antibodies formed as a result of glycosylation mistakes or de-sialylation of polysaccharide chains. We assume that when the GC is overloaded with lipids, other less specialised GGEs could make mistakes and synthesise the antigens of these blood groups. Alternatively, under these conditions, the chylomicrons formed in the enterocytes may, under this overload, linger in the post-Golgi compartment, which is temporarily connected to the endosomes. These compartments contain neuraminidases that can cleave off sialic acid, unmasking these blood antigens located below the acid and inducing the production of antibodies.

Following Natural Autoantibodies: Further Immunoserological Evidence Regarding Their Silent Plasticity and Engagement in Immune Activation

Contradictory reports are available on vaccine-associated hyperstimulation of the immune system, provoking the formation of pathological autoantibodies. Despite being interconnected within the same network, the role of the quieter, yet important non-pathological and natural autoantibodies (nAAbs) is less defined. We hypothesize that upon a prompt immunological trigger, physiological nAAbs also exhibit a moderate plasticity. We investigated their inducibility through aged and recent antigenic triggers. Anti-viral antibodies (anti-MMR n = 1739 and anti-SARS-CoV-2 IgG n = 330) and nAAbs (anti-citrate synthase IgG, IgM n = 1739) were measured by in-house and commercial ELISAs using Croatian (Osijek) anonymous samples with documented vaccination backgrounds. The results were subsequently compared for statistical evaluation. Interestingly, the IgM isotype nAAb showed a statistically significant connection with anti-MMR IgG seropositivity (p < 0.001 in all cases), while IgG isotype nAAb levels were elevated in association with anti-SARS CoV-2 specific seropositivity (p = 0.019) and in heterogeneous vaccine regimen recipients (unvaccinated controls vector/mRNA vaccines p = 0.002). Increasing evidence supports the interplay between immune activation and the dynamic expansion of nAAbs. Consequently, further questions may emerge regarding the ability of nAAbs silently shaping the effectiveness of immunization. We suggest re-evaluating the impact of nAAbs on the complex functioning of the immunological network.

Detection of a natural antibody targeting the shed ectodomain of BP180 in mice

BACKGROUND

Pemphigoid diseases are characterized by subepidermal blister formation accompanied by autoantibodies targeting skin component molecules, such as BP180. It is suggested that an epitope-phenotype correlation exists among autoantibodies recognizing BP180. However, it is unclear which regions of BP180 are likely targets for autoantibodies.

OBJECTIVE

To elucidate the portions of BP180 where antibodies tend to react under the breakdown of immune tolerance.

METHODS

We immunized mice with full-length mouse BP180 (mBP180) to produce anti-mBP180 antibodies. Using the immunized mice, hybridoma cells were established to produce anti-mBP180 antibodies. We analyzed the characteristics of the anti-mBP180 antibodies that were produced in terms of epitopes, immunoglobulin subclasses, and somatic hypermutations.

RESULTS

Hybridoma cells derived from immunized mice with full-length mBP180 produced antibodies targeting the intracellular domain (IC) and the shed ectodomain (EC) of mBP180. Using the domain-deleted mBP180 recombinant protein, we revealed that monoclonal anti-mBP180 EC antibodies react to neoepitopes on the 13th collagenous region of cleaved mBP180, which corresponds to the epitopes of linear IgA bullous dermatosis antibodies in human BP180. Furthermore, the subclasses of these antibodies could be distinguished by epitope: The subclass of the anti-mBP180 IC monoclonal antibodies was IgG, whereas that of the anti-mBP180 EC antibodies was IgM. Of note, a clone of these IgM mBP180 EC antibodies was a germline antibody without somatic hypermutation, which is also known as a natural antibody.

CONCLUSION

These data suggest that mice potentially have natural antibodies targeting the neoepitopes of cleaved mBP180 EC.

Human IgMhiCD300a+ B Cells Are Circulating Marginal Zone Memory B Cells That Respond to Pneumococcal Polysaccharides and Their Frequency Is Decreased in People Living with HIV

CD300a is differentially expressed among B cell subsets, although its expression in immunoglobulin (Ig)M+ B cells is not well known. We identified a B cell subset expressing CD300a and high levels of IgM (IgMhiCD300a+). The results showed that IgMhiCD300a+ B cells were CD10-CD27+CD25+IgDloCD21hiCD23-CD38loCD1chi, suggesting that they are circulating marginal zone (MZ) IgM memory B cells. Regarding the immunoglobulin repertoire, IgMhiCD300a+ B cells exhibited a higher mutation rate and usage of the IgH-VDJ genes than the IgM+CD300a- counterpart. Moreover, the shorter complementarity-determining region 3 (CDR3) amino acid (AA) length from IgMhiCD300a+ B cells together with the predicted antigen experience repertoire indicates that this B cell subset has a memory phenotype. IgM memory B cells are important in T cell-independent responses. Accordingly, we demonstrate that this particular subset secretes higher amounts of IgM after stimulation with pneumococcal polysaccharides or a toll-like receptor 9 (TLR9) agonist than IgM+CD300a- cells. Finally, the frequency of IgMhiCD300a+ B cells was lower in people living with HIV-1 (PLWH) and it was inversely correlated with the years with HIV infection. Altogether, these data help to identify a memory B cell subset that contributes to T cell-independent responses to pneumococcal infections and may explain the increase in severe pneumococcal infections and the impaired responses to pneumococcal vaccination in PLWH.

The Dual Role of the Airway Epithelium in Asthma: Active Barrier and Regulator of Inflammation

Chronic airway inflammation is the cornerstone on which bronchial asthma arises, and in turn, chronic inflammation arises from a complex interplay between environmental factors such as allergens and pathogens and immune cells as well as structural cells constituting the airway mucosa. Airway epithelial cells (AECs) are at the center of these processes. On the one hand, they represent the borderline separating the body from its environment in order to keep inner homeostasis. The airway epithelium forms a multi-tiered, self-cleaning barrier that involves an unstirred, discontinuous mucous layer, the dense and rigid mesh of the glycocalyx, and the cellular layer itself, consisting of multiple, densely interconnected cell types. On the other hand, the airway epithelium represents an immunologically highly active tissue once its barrier has been penetrated: AECs play a pivotal role in releasing protective immunoglobulin A. They express a broad spectrum of pattern recognition receptors, enabling them to react to environmental stressors that overcome the mucosal barrier. By releasing alarmins-proinflammatory and regulatory cytokines-AECs play an active role in the formation, strategic orientation, and control of the subsequent defense reaction. Consequently, the airway epithelium is of vital importance to chronic inflammatory diseases, such as asthma.

Antibody-Mediated Clearance of Brain Amyloid-β: Mechanisms of Action, Effects of Natural and Monoclonal Anti-Aβ Antibodies, and Downstream Effects

Immunotherapeutic efforts to slow the clinical progression of Alzheimer's disease (AD) by lowering brain amyloid-β (Aβ) have included Aβ vaccination, intravenous immunoglobulin (IVIG) products, and anti-Aβ monoclonal antibodies. Neither Aβ vaccination nor IVIG slowed disease progression. Despite conflicting phase III results, the monoclonal antibody Aducanumab received Food and Drug Administration (FDA) approval for treatment of AD in June 2021. The only treatments unequivocally demonstrated to slow AD progression to date are the monoclonal antibodies Lecanemab and Donanemab. Lecanemab received FDA approval in January 2023 based on phase II results showing lowering of PET-detectable Aβ; phase III results released at that time indicated slowing of disease progression. Topline results released in May 2023 for Donanemab's phase III trial revealed that primary and secondary end points had been met. Antibody binding to Aβ facilitates its clearance from the brain via multiple mechanisms including promoting its microglial phagocytosis, activating complement, dissolving fibrillar Aβ, and binding of antibody-Aβ complexes to blood-brain barrier receptors. Antibody binding to Aβ in peripheral blood may also promote cerebral efflux of Aβ by a peripheral sink mechanism. According to the amyloid hypothesis, for Aβ targeting to slow AD progression, it must decrease downstream neuropathological processes including tau aggregation and phosphorylation and (possibly) inflammation and oxidative stress. This review discusses antibody-mediated mechanisms of Aβ clearance, findings in AD trials involving Aβ vaccination, IVIG, and anti-Aβ monoclonal antibodies, downstream effects reported in those trials, and approaches which might improve the Aβ-clearing ability of monoclonal antibodies.

Colistin resistance mutations in phoQ can sensitize Klebsiella pneumoniae to IgM-mediated complement killing

Due to multi-drug resistance, physicians increasingly use the last-resort antibiotic colistin to treat infections with the Gram-negative bacterium Klebsiella pneumoniae. Unfortunately, K. pneumoniae can also develop colistin resistance. Interestingly, colistin resistance has dual effects on bacterial clearance by the immune system. While it increases resistance to antimicrobial peptides, colistin resistance has been reported to sensitize certain bacteria for killing by human serum. Here we investigate the mechanisms underlying this increased serum sensitivity, focusing on human complement which kills Gram-negatives via membrane attack complex (MAC) pores. Using in vitro evolved colistin resistant strains and a fluorescent MAC-mediated permeabilization assay, we showed that two of the three tested colistin resistant strains, Kp209_CSTR and Kp257_CSTR, were sensitized to MAC. Transcriptomic and mechanistic analyses focusing on Kp209_CSTR revealed that a mutation in the phoQ gene locked PhoQ in an active state, making Kp209_CSTR colistin resistant and MAC sensitive. Detailed immunological assays showed that complement activation on Kp209_CSTR in human serum required specific IgM antibodies that bound Kp209_CSTR but did not recognize the wild-type strain. Together, our results show that developing colistin resistance affected recognition of Kp209_CSTR and its killing by the immune system.

Broad responses to chemical adducts shape the natural antibody repertoire in early infancy

Natural antibodies are an integral part of innate humoral immunity yet their development and polyreactive nature are still enigmatic. Here, we show that characteristic monoclonal natural antibodies recognize common chemical moieties or adducts, supporting the view that polyreactive antibodies may often correspond to anti-adduct antibodies. We next examined the development of immunoglobulin M (IgM) and IgG to 81 ubiquitous adducts from birth to old age. Newborn IgM only reacted to a limited number of consensus determinants. This highly restricted neonatal repertoire abruptly diversified around 6 months of age through the development of antibodies to environmental antigens and age-driven epigenetic modifications. In contrast, the IgG repertoire was diverse across the entire life span. Our studies reveal an unrecognized component of humoral immunity directed to common adducts. These findings set the ground for further investigations into the role of anti-adduct B cell responses in homeostatic functions and pathological conditions.

SARS-CoV-2 Infection in Venezuelan Pediatric Patients-A Single Center Prospective Observational Study

Several studies suggest that children infected with SARS-CoV-2 have fewer clinical manifestations than adults; when they develop symptoms, they rarely progress to severe disease. Different immunological theories have been proposed to explain this phenomenon. In September 2020, 16% of the active COVID-19 cases in Venezuela were children under 19 years. We conducted a cross-sectional study of pediatric patients' immune response and clinical conditions with SARS-CoV-2 infection. The patients were admitted to the COVID-19 area of the emergency department of Dr José Manuel de los Ríos Children's Hospital (2021-2022). The lymphocyte subpopulations were analyzed by flow cytometry, and IFNγ, IL-6, and IL-10 serum concentrations were quantified using commercial ELISA assays. The analysis was conducted on 72 patients aged one month to 18 years. The majority, 52.8%, had mild disease, and 30.6% of the patients were diagnosed with MIS-C. The main symptoms reported were fever, cough, and diarrhea. A correlation was found between IL-10 and IL-6 concentrations and age group, lymphocyte subpopulations and nutritional status and steroid use, and IL-6 concentrations and clinical severity. The results suggest a different immune response depending on age and nutritional status that should be considered for treating pediatric COVID-19 patients.

Natural autoimmunity in oligoarticular juvenile idiopathic arthritis

BACKGROUND

Oligoarticular juvenile idiopathic arthritis (oligo-JIA) is considered as an antigen-driven lymphocyte-mediated autoimmune disease. Natural antibodies (NAbs) are pre-immune antibodies produced in the absence of exogenous antigen stimulation, participating in both, innate and adaptive immunity. Considering their major immunoregulatory role in homeostasis and autoimmune pathogenesis, we designed this study to further elucidate their role in oligo-JIA pathogenesis.

METHODS

Seventy children with persistent oligo-JIA and 20 healthy matched controls were enrolled in the study. Serum IgM and IgA antibodies against human G-actin, human IgG F(ab΄)2 fragments and the hapten TriNitroPhenol (TNP) as well as the total concentration of serum IgM and IgA were measured by in-house enzyme-immunoassays. Kolmogorov-Smirnov normality test, Kruskal-Wallis H and Mann-Whitney tests were used to assess data distribution, and significant differences of non-parametric data between groups of the study. Backward regression analysis was used to analyze the effect of multiple factors (age, gender, disease activity, anti-nuclear antibody positivity, presence of uveitis) on continuous dependent variables (activities and activity/ concentration ratios of IgM and IgA NAbs).

RESULTS

The ratios of IgA anti-TNP, anti-actin and anti-F(ab΄)₂ levels to total serum IgA concentration were found to be significantly increased in patients with oligo-JIA compared to healthy subjects. Significantly elevated levels of IgM anti-TNP antibodies were also found in children with inactive oligo-JIA compared to those of children with active disease and of healthy controls. In the presence of anterior uveitis, IgM anti-TNP levels were significantly higher than in patients without uveitis or in healthy controls. Backward regression analysis revealed that the disease activity and the presence of anterior uveitis independently affect IgM anti-TNP levels.

CONCLUSUIONS

Our findings are in accordance with the hypothesis that NAbs contribute to the pathogenesis of autoimmune diseases and provide additional evidence that disturbances in natural autoimmunity may contribute to the as yet unclarified pathogenesis of oligo-JIA.

Highly pathogenic natural monoclonal antibody B4-IgM recognizes a post-translational modification comprised of acetylated N-terminal methionine followed by aspartic or glutamic acid

The natural monoclonal antibody B4-IgM recognizes murine annexin 4 (mAn4) and exacerbates ischemia-reperfusion injury in many mouse models. During apoptosis, the intracellular mAn4 protein translocates to the membrane surface, remaining attached to the outer membrane leaflet where it is recognized by the anti-mAn4 B4-IgM antibody. B4-IgM does not recognize human annexin 4 (hAn4). However, the B4-IgM antibody epitope was detected by Western blot of unknown human proteins and by flow cytometry on all studied human cell lines undergoing apoptosis and on a minor subset of healthy cells. The B4-IgM antibody also recognizes the epitope on necrotic cells in cytoplasmic proteins, apparently entering through pores large enough to allow natural antibodies to penetrate the cells and bind to the epitope expressed on self-proteins. Using proteomics and site-directed mutagenesis, we found that B4-IgM binds to an epitope with post-translationally modified acetylated N-terminal methionine, followed by either glutamic or aspartic acid. The epitope is not induced by apoptosis or injury because this modification can also occur during protein translation. This finding reveals an additional novel mechanism whereby injured cells are detected by natural antibodies that initiate pathogenic complement activation through the recognition of epitopes that are shared across multiple proteins found in variable cell lines.

Mercury-Modulated Immune Responses in Arctic Barnacle Goslings (Branta leucopsis) upon a Viral-Like Immune Challenge

Historical mining activities in Svalbard (79°N/12°E) have caused local mercury (Hg) contamination. To address the potential immunomodulatory effects of environmental Hg on Arctic organisms, we collected newborn barnacle goslings (Branta leucopsis) and herded them in either a control or mining site, differing in Hg levels. An additional group at the mining site was exposed to extra inorganic Hg(II) via supplementary feed. Hepatic total Hg concentrations differed significantly between the control (0.011 ± 0.002 mg/kg dw), mine (0.043 ± 0.011 mg/kg dw), and supplementary feed (0.713 ± 0.137 mg/kg dw) gosling groups (average ± standard deviation). Upon immune challenge with double-stranded RNA (dsRNA) injection, endpoints for immune responses and oxidative stress were measured after 24 h. Our results indicated that Hg exposure modulated the immune responses in Arctic barnacle goslings upon a viral-like immune challenge. Increased exposure to both environmental as well as supplemental Hg reduced the level of natural antibodies, suggesting impaired humoral immunity. Hg exposure upregulated the expression of proinflammatory genes in the spleen, including inducible nitric oxide synthase (iNOS) and interleukin 18 (IL18), suggesting Hg-induced inflammatory effects. Exposure to Hg also oxidized glutathione (GSH) to glutathione disulfide (GSSG); however, goslings were capable of maintaining the redox balance by de novo synthesis of GSH. These adverse effects on the immune responses indicated that even exposure to low, environmentally relevant levels of Hg might affect immune competence at the individual level and might even increase the susceptibility of the population to infections.

ABO blood groups and nosocomial infection

The timely identification of the high-risk groups for nosocomial infections (NIs) plays a vital role in its prevention and control. Therefore, it is crucial to investigate whether the ABO blood group is a risk factor for NI. In this study, patients with NI and non-infection were matched by the propensity score matching method and a logistic regression model was used to analyse the matched datasets. The study found that patients with the B&AB blood group were susceptible to Escherichia coli (OR = 1.783, p = 0.039); the A blood group were susceptible to Staphylococcus aureus (OR = 2.539, p = 0.019) and Pseudomonas aeruginosa (OR = 5.724, p = 0.003); the A&AB blood group were susceptible to Pseudomonas aeruginosa (OR = 4.061, p = 0.008); the AB blood group were vulnerable to urinary tract infection (OR = 13.672, p = 0.019); the B blood group were susceptible to skin and soft tissue infection (OR = 2.418, p = 0.016); and the B&AB blood group were vulnerable to deep incision infection (OR = 4.243, p = 0.043). Summarily, the patient's blood group is vital for identifying high-risk groups for NIs and developing targeted prevention and control measures for NIs.

Uncovering tau in wasteosomes (corpora amylacea) of Alzheimer’s disease patients

Brain corpora amylacea, recently renamed as wasteosomes, are polyglucosan bodies that appear during aging and some neurodegenerative conditions. They collect waste substances and are part of a brain cleaning mechanism. For decades, studies on their composition have produced inconsistent results and the presence of tau protein in them has been controversial. In this work, we reanalyzed the presence of this protein in wasteosomes and we pointed out a methodological problem when immunolabeling. It is well known that to detect tau it is necessary to perform an antigen retrieval. However, in the case of wasteosomes, an excessive antigen retrieval with boiling dissolves their polyglucosan structure, releases the entrapped proteins and, thus, prevents their detection. After performing an adequate pre-treatment, with an intermediate time of boiling, we observed that some brain wasteosomes from patients with Alzheimer’s disease (AD) contained tau, while we did not detect tau protein in those from non-AD patients. These observations pointed the different composition of wasteosomes depending on the neuropathological condition and reinforce the role of wasteosomes as waste containers.

Complexity of the Immune Response Elicited by Different COVID-19 Vaccines, in the Light of Natural Autoantibodies and Immunomodulatory Therapies

Despite the abundance of data on the COVID-19 vaccine-induced immune activation, the impact of natural autoantibodies (nAAbs) on these processes is less well defined. Therefore, we investigated potential connections between vaccine efficacy and nAAb levels. We were also interested in the impact of immunomodulatory therapies on vaccine efficacy. Clinical residual samples were used for the assessment of the COVID-19 vaccine-elicited immune response (IR) (n=255), as well as for the investigation of the immunization-associated expansion of the nAAb pool (n=185). In order to study the potential interaction between immunomodulatory therapies and the vaccine-induced IR, untreated, healthy individuals and patients receiving anti-TNFα or anti-IL-17 therapies were compared (n total =45). In-house ELISAs (anticitrate synthase, anti-HSP60 and-70) and commercial ELISAs (anti-SARS-CoV-2 ELISAs IgG, IgA, NeutraLISA and IFN-γ release assay 'IGRA') were applied. We found significant differences in the IR given to different vaccines. Moreover, nAAb levels showed plasticity in response to anti-COVID-19 immunization. We conclude that our findings may support the theorem about the non-specific beneficial 'side effects' of vaccination, including the broadening of the nAAb repertoire. Considering immunomodulation, we suggest that anti-TNFα and anti-IL17 treatments may interfere negatively with MALT-associated IR, manifested as decreased IgA titers; however, the modest sample numbers of the herein presented model might be a limiting factor of reaching a more comprehensive conclusion.

The characters of antibodies against PLA2R in healthy individuals and in the patient with PLA2R associated membranous nephropathy

BACKGROUND

Most primary membranous nephropathy (MN) is mediated by anti-phospholipase A2 receptor (PLA2R) antibodies. Recently, these antibodies have been revealed months to years before the disease's onset. Their production and pathogenicity need further investigation.

METHODS

Anti-PLA2R antibodies were purified from plasma of eight healthy individuals, 12 patients with PLA2R-related MN and negative circulating antibody (Ab-), and 18 patients with positive anti-PLA2R antibodies (Ab +), using affinity column coupled with recombinant human PLA2R. The antigen specificity, antibody amount, titer, IgG subclass, and affinity were assessed by Western blot, immunofluorescence, ELISA, and surface plasmon resonance.

RESULTS

The natural anti-PLA2R antibodies recognized the conformational structure of PLA2R which locates on the cell membrane of podocytes. The amount of natural IgG was 0.12 ± 0.04 g/L, which accounted for 0.80% of total IgG and was lower than that of patients (2.36%, P < 0.001). The titer of natural antibodies was lower than that of patients in Ab- and Ab + groups (1:16 vs. 1:43 vs. 1:274, P < 0.001). IgG2(45.1%) was predominant in natural antibodies, while IgG4 was predominant in Ab + group (45.7 vs. 25.0%, P < 0.001). IgG1 was increasing from natural antibodies to Ab- and Ab + groups. The affinity of natural antibodies was lower than that of patients (K_D: 641.0 vs. 269.0 vs. 99.6 nM, P = 0.002). The antibody titer, affinity, and IgG4 percentage were associated with the severity of proteinuria and the stages of membranous lesion.

CONCLUSIONS

The natural anti-PLA2R antibodies exist in healthy plasma. The antibody titer, IgG subclass, and affinity may participate in the pathogenesis of anti-PLA2R antibodies.

COVID-19 Disease in Under-5 Children: Current Status and Strategies for Prevention including Vaccination

Since the coronavirus disease (COVID-19) pandemic hit the globe in early 2020, we have steadily gained insight into its pathogenesis; thereby improving surveillance and preventive measures. In contrast to other respiratory viruses, neonates and young children infected with severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) have a milder clinical presentation, with only a small proportion needing hospitalization and intensive care support. With the emergence of novel variants and improved testing services, there has been a higher incidence of COVID-19 disease reported among children and neonates. Despite this, the proportion of young children with severe disease has not increased. Key mechanisms that protect young children from severe COVID-19 disease include the placental barrier, differential expression of angiotensin-converting enzyme 2 (ACE-2) receptors, immature immune response, and passive transfer of antibodies via placenta and human milk. Implementing mass vaccination programs has been a major milestone in reducing the global disease burden. However, considering the lower risk of severe COVID-19 illness in young children and the limited evidence about long-term vaccine safety, the risk-benefit balance in children under five years of age is more complex. In this review, we do not support or undermine vaccination of young children but outline current evidence and guidelines, and highlight controversies, knowledge gaps, and ethical issues related to COVID-19 vaccination in young children. Regulatory bodies should consider the individual and community benefits of vaccinating younger children in their local epidemiological setting while planning regional immunization policies.

Stimulation of naïve B cells with a fusion protein consisting of FlaA and Bet v 1 induces regulatory B cells ex vivo

BACKGROUND

The experimental fusion protein rFlaA:Betv1 was shown to efficiently suppress allergen-specific sensitization in mice. However, the detailed mechanism of rFlaA:Betv1-mediated immune modulation is not fully understood. In this study, we investigated the effect of rFlaA:Betv1 on naïve murine B cells.

METHODS

Immune modulating capacity of rFlaA:Betv1 was screened in IL-10 reporter mice. B cells were isolated from spleens of naïve C57Bl/6, TLR5^-/- , or MyD88^-/- mice, stimulated with rFlaA:Betv1 and controls, and monitored for the expression of the regulatory B cell markers CD1d, CD24, CD38, and surface IgM by flow cytometry. Secreted cytokines, antibodies, and reactivity of the induced antibodies were investigated by ELISA and intracellular flow cytometry. Suppressive capacity of rFlaA:Betv1-stimulated B cells was tested in mDC:CD4⁺ T cell:B cell triple cultures.

RESULTS

Upon in vivo application of rFlaA:Betv1 into IL-10-GFP reporter mice, CD19⁺ B cells were shown to produce anti-inflammatory IL-10, suggesting B cells to contribute to the immune-modulatory properties of rFlaA:Betv1. rFlaA:Betv1-induced IL-10 secretion was confirmed in human B cells isolated from buffy coats. In vitro stimulation of naïve murine B cells with rFlaA:Betv1 resulted in an mTOR- and MyD88-dependent production of IL-10 and rFlaA:Betv1 induced Bet v 1-reactive IgG production, which was not observed for IgA. rFlaA:Betv1-stimulated B cells formed a CD19⁺ CD24⁺ CD1d⁺ IgM⁺ CD38⁺ Breg subpopulation capable of suppressing Bet v 1-induced TH2 cytokine secretion in vitro.

CONCLUSION

rFlaA:Betv1 can act as a thymus-independent B cell antigen, stimulating the mTOR- and MyD88-dependent differentiation of B cells displaying a regulatory phenotype, IL-10 secretion, antigen-binding antibody production, and a suppressive capacity in vitro.

Strategies for HIV-1 vaccines that induce broadly neutralizing antibodies

After nearly four decades of research, a safe and effective HIV-1 vaccine remains elusive. There are many reasons why the development of a potent and durable HIV-1 vaccine is challenging, including the extraordinary genetic diversity of HIV-1 and its complex mechanisms of immune evasion. HIV-1 envelope glycoproteins are poorly recognized by the immune system, which means that potent broadly neutralizing antibodies (bnAbs) are only infrequently induced in the setting of HIV-1 infection or through vaccination. Thus, the biology of HIV-1-host interactions necessitates novel strategies for vaccine development to be designed to activate and expand rare bnAb-producing B cell lineages and to select for the acquisition of critical improbable bnAb mutations. Here we discuss strategies for the induction of potent and broad HIV-1 bnAbs and outline the steps that may be necessary for ultimate success.

The Role of Immunity in the Pathogenesis of SARS-CoV-2 Infection and in the Protection Generated by COVID-19 Vaccines in Different Age Groups

This study aims to review the available data regarding the central role of immunity in combating SARS-CoV-2 infection and in the generation of protection by vaccination against COVID-19 in different age groups. Physiologically, the immune response and the components involved in it are variable, both functionally and quantitatively, in neonates, infants, children, adolescents, and adults. These immunological differences are mirrored during COVID-19 infection and in the post-vaccination period. The outcome of SARS-CoV-2 infection is greatly dependent on the reaction orchestrated by the immune system. This is clearly obvious in relation to the clinical status of COVID-19 infection, which can be symptomless, mild, moderate, or severe. Even the complications of the disease show a proportional pattern in relation to the immune response. On the contrary, the commonly used anti-COVID-19 vaccines generate protective humoral and cellular immunity. The magnitude of this immunity and the components involved in it are discussed in detail. Furthermore, many of the adverse effects of these vaccines can be explained on the basis of immune reactions against the different components of the vaccines. Regarding the appropriate choice of vaccine for different age groups, many factors have to be considered. This is a cornerstone, particularly in the following age groups: 1 day to 5 years, 6 to 11 years, and 12 to 17 years. Many factors are involved in deciding the route, doses, and schedule of vaccination for children. Another important issue in this dilemma is the hesitancy of families in making the decision about whether to vaccinate their children. Added to these difficulties is the choice by health authorities and governments concerning whether to make children's vaccination compulsory. In this respect, although rare and limited, adverse effects of vaccines in children have been detected, some of which, unfortunately, have been serious or even fatal. However, to achieve comprehensive control over COVID-19 in communities, both children and adults have to be vaccinated, as the former group represents a reservoir for viral transmission. The understanding of the various immunological mechanisms involved in SARS-CoV-2 infection and in the preparation and application of its vaccines has given the sciences a great opportunity to further deepen and expand immunological knowledge. This will hopefully be reflected positively on other diseases through gaining an immunological background that may aid in diagnosis and therapy. Humanity is still in continuous conflict with SARS-CoV-2 infection and will be for a while, but the future is expected to be in favor of the prevention and control of this disease.

Enhancer-instructed epigenetic landscape and chromatin compartmentalization dictate a primary antibody repertoire protective against specific bacterial pathogens

Antigen receptor loci are organized into variable (V), diversity (D) and joining (J) gene segments that rearrange to generate antigen receptor repertoires. Here, we identified an enhancer (E34) in the murine immunoglobulin kappa (Igk) locus that instructed rearrangement of Vκ genes located in a sub-topologically associating domain, including a Vκ gene encoding for antibodies targeting bacterial phosphorylcholine. We show that E34 instructs the nuclear repositioning of the E34 sub-topologically associating domain from a recombination-repressive compartment to a recombination-permissive compartment that is marked by equivalent activating histone modifications. Finally, we found that E34-instructed Vκ-Jκ rearrangement was essential to combat Streptococcus pneumoniae but not methicillin-resistant Staphylococcus aureus or influenza infections. We propose that the merging of Vκ genes with Jκ elements is instructed by one-dimensional epigenetic information imposed by enhancers across Vκ and Jκ genomic regions. The data also reveal how enhancers generate distinct antibody repertoires that provide protection against lethal bacterial infection.

Further analysis of natural antibodies against ischemic stroke

Background

Our previous study revealed that circulating levels of IgG natural antibodies (NAbs) for vascular endothelial growth factor receptor 1 (VEGFR1) were significantly decreased in patients with arteriosclerosis compared with control subjects. To enhance the sensitivity of an enzyme-linked immunosorbent assay (ELISA) developed in-house for antibody testing, the present work was designed to investigate additive signals in the in-house ELISA developed with the combination of two or more linear peptide antigens derived from target proteins of interest, including VEGFR1, oxidized low-density lipoprotein receptor 1 (LOX-1), interleukins 6 (IL6) and 8 (IL8).

Methods

A total of 218 patients with ischemic stroke and 198 healthy controls were enrolled and an in-house ELISA was developed with linear peptides derived from VEGFR1, LOX-1, IL6, and IL8 to detect their IgG levels in plasma.

Results

Compared with control subjects, plasma levels of IgG NAbs for the IL6-IL8 combination were significantly lower in female patients (Z = -3.149, P = 0.002), whereas male patients showed significantly lower levels of plasma anti-VEGFR IgG (Z = -3.895, P < 0.001) and anti-LOX1a IgG (Z = -4.329, P < 0.001). Because plasma levels of IgG NAbs for both the IL6-IL8-LOX1a-LOX1b combination and the VEGFR1a-VEGFR1b-LOX1a-LOX1b combination were significantly lower in the patient group than the control group, receiver operating characteristic (ROC) analysis was performed and the results showed that the VEGFR1a-VEGFR1b-LOX1a-LOX1b combination had an area under the ROC curve (AUC) of 0.70 for its IgG assay with a sensitivity of 27.1% against the specificity of 95.5% and that the IL6-IL8-LOX1a-LOX1b combination had an AUC of 0.67 for its IgG assay with a sensitivity of 21.1% against the specificity of 95.5%. Spearman correlation analysis showed that plasma IgG NAbs against the IL6-IL8 combination were positively correlated with carotid plaque size only in male patients (r = 0.270, p = 0.002).

Conclusions

Circulating IgG NAbs for the target molecules studied may be potential biomarkers for a subgroup of ischemic stroke and also contribute to the gender differences in clinical presentation of the disease.

Age-related changes in antigen-specific natural antibodies are influenced by sex

Introduction

Natural antibody (NAb) derived from CD5+ B-1 cells maintains tissue homeostasis, controls inflammation, aids in establishing long-term protective responses against pathogens, and provides immediate protection from infection. CD5+ B-1 cell NAbs recognize evolutionarily fixed epitopes, such as phosphatidylcholine (PtC), found on bacteria and senescent red blood cells. Anti-PtC antibodies are essential in protection against bacterial sepsis. CD5+ B-1 cell-derived NAbs have a unique germline-like structure that lacks N-additions, a feature critical for providing protection against infection. Previously, we demonstrated the repertoire and germline status of PtC+CD5+ B-1 cell IgM obtained from male mice changes with age depending on the anatomical location of the B-1 cells. More recently, we demonstrated serum antibody from aged female mice maintains protection against pneumococcal infection, whereas serum antibody from male mice does not provide protection.

Results

Here, we show that aged female mice have significantly more splenic PtC+CD5+ B-1 cells and more PtC specific serum IgM than aged male mice. Furthermore, we find both age and biological sex related repertoire differences when comparing B cell receptor (BCR) sequencing results of PtC+CD5+ B-1 cells. While BCR germline status of PtC+CD5+ B-1 cells from aged male and female mice is similar in the peritoneal cavity, it differs significantly in the spleen, where aged females retain germline configuration and aged males do not. Nucleic acid sensing toll-like receptors are critical in the maintenance of PtC+ B-1 cells; therefore, to begin to understand the mechanism of differences observed between the male and female PtC+CD5+ B-1 cell repertoire, we analyzed levels of cell-free nucleic acids and found increases in aged females.

Conclusion

Our results suggest the antigenic milieu differs between aged males and females, leading to differential selection of antigen-specific B-1 cells over time. Further elucidation of how biological sex differences influence the maintenance of B-1 cells within the aging environment will be essential to understand sex and age-related disparities in the susceptibility to bacterial infection and will aid in the development of more effective vaccination and/or therapeutic strategies specific for males and females.

IgA-producing B cells in lung homeostasis and disease

Immunoglobulin A (IgA) is the most abundant Ig in mucosae where it plays key roles in host defense against pathogens and in mucosal immunoregulation. Whereas intense research has established the different roles of secretory IgA in the gut, its function has been much less studied in the lung. This review will first summarize the state-of-the-art knowledge on the distribution and phenotype of IgA⁺ B cells in the human lung in both homeostasis and disease. Second, it will analyze the studies looking at cellular and molecular mechanisms of homing and priming of IgA⁺ B cells in the lung, notably following immunization. Lastly, published data on observations related to IgA and IgA⁺ B cells in lung and airway disease such as asthma, cystic fibrosis, idiopathic pulmonary fibrosis, or chronic rhinosinusitis, will be discussed. Collectively it provides the state-of-the-art of our current understanding of the biology of IgA-producing cells in the airways and identifies gaps that future research should address in order to improve mucosal protection against lung infections and chronic inflammatory diseases.

Adaptive Immunity in Reptiles: Conventional Components but Unconventional Strategies

Recent studies have established that the innate immune system of reptiles is broad and robust, but the question remains: What role does the reptilian adaptive immune system play? Conventionally, adaptive immunity is described as involving T and B lymphocytes that display variable receptors, is highly specific, improves over the course of the response, and produces a memory response. While reptiles do have B and T lymphocytes that utilize variable receptors, their adaptive response is relatively non-specific, generates a prolonged antibody response, and does not produce a typical memory response. This alternative adaptive strategy may allow reptiles to produce a broad adaptive response that complements a strong innate system. Further studies into reptile adaptive immunity cannot only clarify outstanding questions on the reptilian immune system but can shed light on a number of important immunological concepts, including the evolution of the immune system and adaptive immune responses that take place outside of germinal centers.

Forward genetic screen of homeostatic antibody levels in the Collaborative Cross identifies MBD1 as a novel regulator of B cell homeostasis

Variation in immune homeostasis, the state in which the immune system is maintained in the absence of stimulation, is highly variable across populations. This variation is attributed to both genetic and environmental factors. However, the identity and function of specific regulators have been difficult to identify in humans. We evaluated homeostatic antibody levels in the serum of the Collaborative Cross (CC) mouse genetic reference population. We found heritable variation in all antibody isotypes and subtypes measured. We identified 4 quantitative trait loci (QTL) associated with 3 IgG subtypes: IgG1, IgG2b, and IgG2c. While 3 of these QTL map to genome regions of known immunological significance (major histocompatibility and immunoglobulin heavy chain locus), Qih1 (associated with variation in IgG1) mapped to a novel locus on Chromosome 18. We further associated this locus with B cell proportions in the spleen and identify Methyl-CpG binding domain protein 1 under this locus as a novel regulator of homeostatic IgG1 levels in the serum and marginal zone B cells (MZB) in the spleen, consistent with a role in MZB differentiation to antibody secreting cells.

Human B-1 cells are important contributors to the naturally-occurring IgM pool against the tumor-associated ganglioside Neu5GcGM3

Only few studies have described the anti-tumor properties of natural antibodies (NAbs). In particular, natural IgM have been linked to cancer immunosurveillance due to its preferential binding to tumor-specific glycolipids and carbohydrate structures. Neu5GcGM3 ganglioside is a sialic acid-containing glycosphingolipid that has been considered an attractive target for cancer immunotherapy, since it is not naturally expressed in healthy human tissues and it is overexpressed in several tumors. Screening of immortalized mouse peritoneal-derived hybridomas showed that peritoneal B-1 cells contain anti-Neu5GcGM3 antibodies on its repertoire, establishing a link between B-1 cells, NAbs and anti-tumor immunity. Previously, we described the existence of naturally-occurring anti-Neu5GcGM3 antibodies with anti-tumor properties in healthy young humans. Interestingly, anti-Neu5GcGM3 antibodies level decreases with age and is almost absent in non-small cell lung cancer patients. Although anti-Neu5GcGM3 antibodies may be clinically relevant, the identity of the human B cells participating in this anti-tumor antibody response is unknown. In this work, we found an increased percentage of circulating human B-1 cells in healthy individuals with anti-Neu5GcGM3 IgM antibodies. Furthermore, anti-Neu5GcGM3 IgMs were generated predominantly by human B-1 cells and the antibodies secreted by these B-1 lymphocytes also recognized Neu5GcGM3-positive tumor cells. These data suggest a protective role for human B-1 cells against malignant transformation through the production of NAbs reactive to tumor-specific antigens such as Neu5GcGM3 ganglioside.

Wasteosomes (corpora amylacea) of human brain can be phagocytosed and digested by macrophages

Background

Corpora amylacea of human brain, recently renamed as wasteosomes, are granular structures that appear during aging and also accumulate in specific areas of the brain in neurodegenerative conditions. Acting as waste containers, wasteosomes are formed by polyglucosan aggregates that entrap and isolate toxic and waste substances of different origins. They are expelled from the brain to the cerebrospinal fluid (CSF), and can be phagocytosed by macrophages. In the present study, we analyze the phagocytosis of wasteosomes and the mechanisms involved in this process. Accordingly, we purified wasteosomes from post-mortem extracted human CSF and incubated them with THP-1 macrophages. Immunofluorescence staining and time-lapse recording techniques were performed to evaluate the phagocytosis. We also immunostained human hippocampal sections to study possible interactions between wasteosomes and macrophages at central nervous system interfaces.

Results

We observed that the wasteosomes obtained from post-mortem extracted CSF are opsonized by MBL and the C3b complement protein. Moreover, we observed that CD206 and CD35 receptors may be involved in the phagocytosis of these wasteosomes by THP-1 macrophages. Once phagocytosed, wasteosomes become degraded and some of the resulting fractions can be exposed on the surface of macrophages and interchanged between different macrophages. However, brain tissue studies show that, in physiological conditions, CD206 but not CD35 receptors may be involved in the phagocytosis of wasteosomes.

Conclusions

The present study indicates that macrophages have the machinery required to process and degrade wasteosomes, and that macrophages can interact in different ways with wasteosomes. In physiological conditions, the main mechanism involve CD206 receptors and M2 macrophages, which trigger the phagocytosis of wasteosomes without inducing inflammatory responses, thus avoiding tissue damage. However, altered wasteosomes like those obtained from post-mortem extracted CSF, which may exhibit waste elements, become opsonized by MBL and C3b, and so CD35 receptors constitute another possible mechanism of phagocytosis, leading in this case to inflammatory responses.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13578-022-00915-2.

Natural Antibodies Alert the Adaptive Immune System of the Presence of Transformed Cells in Early Tumorigenesis

Recent studies have revealed a critical role for natural Abs (NAbs) in antitumor immune responses. However, the role of NAbs in cancer immunosurveillance remains unexplored, mainly because of the lack of in vivo models that mimic the early recognition and elimination of transforming cells. In this article, we propose a role for NAbs in alerting the immune system against precancerous neoantigen-expressing cells immediately after they escape intrinsic tumor suppression mechanisms. We identify four distinct reproducible, trackable, MHC-matched neoantigen-expressing cell models that do not form tumors as the end point. This amplified readout in the critical window prior to tumor formation allows investigation of new mediators of cancer immunosurveillance. We found that neoantigen-expressing cells adoptively transferred in NAb-deficient mice persisted, whereas they were eliminated in wild-type mice, indicating that the circulating NAb repertoire alerts the immune system to the presence of transformed cells. Moreover, immunity is mounted against immunogenic and nonimmunogenic neoantigens contained in the NAb-tagged cells, regardless of whether the NAb directly recognizes the neoantigens. Beyond these neoantigen-expressing model systems, we observed a significantly greater tumor burden in chemically and virally induced tumor models in NAb-deficient mice compared with wild-type mice. Restoration of the NAb repertoire in NAb-deficient mice elicited the recognition and elimination of neoantigen-expressing cells and cancer. These data show that NAbs are required and sufficient for elimination of transformed cells early in tumorigenesis. These models can now be used to investigate how NAbs stimulate immunity via recognition receptors to eliminate precancerous cells.

Role of microRNAs in B-Cell Compartment: Development, Proliferation and Hematological Diseases

B-cell development is a very orchestrated pathway that involves several molecules, such as transcription factors, cytokines, microRNAs, and also different cells. All these components maintain the ideal microenvironment and control B-cell differentiation. MicroRNAs are small non-coding RNAs that bind to target mRNA to control gene expression. These molecules could circulate in the body in a free form, protein-bounded, or encapsulated into extracellular vesicles, such as exosomes. The comprehension of the role of microRNAs in the B-cell development was possible based on microRNA profile of each B-cell stage and functional studies. Herein, we report the knowledge about microRNAs in the B-cell the differentiation, proliferation, and also in hematological malignancies.

The Forgotten Brother: The Innate-like B1 Cell in Multiple Sclerosis

Multiple sclerosis (MS) is a neurodegenerative disease of the central nervous system (CNS), traditionally considered a chronic autoimmune attack against the insulating myelin sheaths around axons. However, the exact etiology has not been identified and is likely multi-factorial. Recently, evidence has been accumulating that implies that autoimmune processes underlying MS may, in fact, be triggered by pathological processes initiated within the CNS. This review focuses on a relatively unexplored immune cell-the "innate-like" B1 lymphocyte. The B1 cell is a primary-natural-antibody- and anti-inflammatory-cytokine-producing cell present in the healthy brain. It has been recently shown that its frequency and function may differ between MS patients and healthy controls, but its exact involvement in the MS pathogenic process remains obscure. In this review, we propose that this enigmatic cell may play a more prominent role in MS pathology than ever imagined. We aim to shed light on the human B1 cell in health and disease, and how dysregulation in its delicate homeostatic role could impact MS. Furthermore, novel therapeutic avenues to restore B1 cells' beneficial functions will be proposed.

Bovine Natural Antibody Relationships to Specific Antibodies and Fasciola hepatica Burdens after Experimental Infection and Vaccination with Glutathione S-Transferase

Fasciola hepatica is the causative agent of fasciolosis, a significant parasitic disease occurring worldwide. Despite ongoing efforts, there is still no vaccine to control liver fluke infections in livestock. Recently, it has been suggested that natural antibodies (NAbs) can amplify specific antibodies (SpAb) and have a direct killing effect, but it is unknown if this phenomenon occurs during parasitic helminth infection or targeted vaccination. NAbs are antibodies produced by the innate immune system, capable of binding antigens without prior exposure. This study explores the role of bovine NAbs, using the exogenous glycoprotein keyhole limpet hemocyanin (KLH), in response to F. hepatica infection and SpAb production after infection and vaccination. The cattle’s NAbs were differently influenced by parasite infection and vaccination, with an increase in KLH-binding IgG and IgM levels after infection and reduced KLH-binding IgM levels following vaccination. Underlying NAbs reacting to KLH showed no correlations to the final fluke burdens after experimental infection or vaccination. However, NAbs reacting to whole-worm extract (WWE) prior to infection were positively correlated to increased fluke burdens within the infected bovine host. Furthermore, after infection, the specific IgG reacting to WWE was positively reflected by the underlying NAb IgG response. Following subcutaneous vaccination with F. hepatica native glutathione S-transferase (GST), there was a non-significant 33% reduction in fluke burden. Vaccinated animals with higher underlying NAbs had a higher induction of vaccine-induced SpAbs, with trends observed between KLH-binding IgM and anti-GST IgG and IgM. Our findings provide a platform to allow further investigation to determine if NAb levels could mirror fluke-SpAb production for exploitation in a combined selective breeding and vaccination program. Additionally, this work suggests that liver fluke could possibly evade the host’s immune system by utilising surface-bound IgM NAbs.

The Different Immune Responses by Age Are due to the Ability of the Fetal Immune System to Secrete Primal Immunoglobulins Responding to Unexperienced Antigens

Among numerous studies on coronavirus 2019 (COVID-19), we noted that the infection and mortality rates of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) increased with age and that fetuses known to be particularly susceptible to infection were better protected despite various mutations. Hence, we established the hypothesis that a new immune system exists that forms before birth and decreases with aging.

Methods: To prove this hypothesis, we established new ex-vivo culture conditions simulating the critical environmental factors of fetal stem cells (FSCs) in early pregnancy. Then, we analyzed the components from FSCs cultivated newly developed ex-vivo culture conditions and compared them from FSCs cultured in a normal condition.

Results: We demonstrated that immunoglobulin M (IgM), a natural antibody (NAb) produced only in early B-1 cells, immunoglobulins (Igs) including IgG3, which has a wide range of antigen-binding capacity and affinity, complement proteins, and antiviral proteins are induced in FSCs only cultured in newly developed ex-vivo culture conditions. Particularly we confirmed that their extracellular vesicles (EVs) contained NAbs, Igs, various complement proteins, and antiviral proteins, as well as human leukocyte antigen G (HLA-G), responsible for immune tolerance.

Conclusion: Our results suggest that FSCs in early pregnancy can form an independent immune system responding to unlearned antigens as a self-defense mechanism before establishing mature immune systems. Moreover, we propose the possibility of new solutions to cope with various infectious diseases based on the factors in NAbs-containing EVs, especially not causing unnecessary immune reaction due to HLA-G.