Memory B and memory plasma cells

Functional Enrichment and Analysis of Antigen-Specific Memory B Cell Antibody Repertoires in PBMCs

Phenotypic screening of antigen-specific antibodies in human blood is a common diagnostic test for infectious agents and a correlate of protection after vaccination. In addition to long-lived antibody secreting plasma cells residing in the bone marrow, memory B cells are a latent source of antigen-experienced, long-term immunity that can be found at low frequencies in circulating peripheral blood mononuclear cells (PBMCs). Assessing the genotype, clonal frequency, quality, and function of antibodies resulting from an individual's persistent memory B cell repertoire can help inform the success or failure of immune protection. Using in vitro polyclonal stimulation, we functionally expand the memory repertoire from PBMCs and clonally map monoclonal antibodies from this population. We show that combining deep sequencing of stimulated memory B cell repertoires with retrieving single antigen-specific cells is a promising approach in evaluating the latent, functional B cell memory in PBMCs.

Approaches to Interrogating the Human Memory B-Cell and Memory-Derived Antibody Repertoire Following Dengue Virus Infection

Memory B-cells (MBCs) are potential antibody secreting immune cells that differentiate and mature following host exposure to a pathogen. Following differentiation, MBCs remain in peripheral circulation after recovery and are poised to secrete antigen-specific antibodies if and when they are re-exposed to their cognate antigen. Consequently, MBCs form the founder population and provide one of the first lines of pathogen-specific defense against reinfection. The role MBCs play is complicated for viruses that are heterologous, such as dengue virus (DENV), which exist as antigenically different serotypes. On second infection with a different serotype, MBCs from initial dengue infection rapidly proliferate and secrete antibodies: many of these MBC derived antibodies will be cross-reactive and weakly neutralizing, while some antibodies may recognize epitopes conserved across serotypes and have the capacity to broadly neutralize 2 or more serotypes. It is also possible that a new population of MBCs and antibodies specific for the second virus serotype need to arise for long-term broader immunity to develop. Methods to interrogate and track memory B cell responses are important for evaluating both natural immunity and vaccine response. However, the low abundance of MBCs for any specific pathogen makes it challenging to interrogate frequency, specificity, and breadth for the pathogen of interest. This review discusses current approaches that have been used to interrogate the memory B cell immune response against viral pathogens in general and DENV specifically. Including strengths, limitations, and future directions. Single-cell approaches could help uncover the DENV specific MBC antibody repertoire, and improved methods for isolating DENV specific monoclonal antibodies from human peripheral blood cells would allow for a functional analysis of the anti-DENV repertoire.

Hypoxia-inducible factors in CD4+ T cells promote metabolism, switch cytokine secretion, and T cell help in humoral immunity

T cell help in humoral immunity includes interactions of B cells with activated extrafollicular CD4⁺ and follicular T helper (Tfh) cells. Each can promote antibody responses but Tfh cells play critical roles during germinal center (GC) reactions. After restimulation of their antigen receptor (TCR) by B cells, helper T cells act on B cells via CD40 ligand and secreted cytokines that guide Ig class switching. Hypoxia is a normal feature of GC, raising questions about molecular mechanisms governing the relationship between hypoxia response mechanisms and T cell help to antibody responses. Hypoxia-inducible factors (HIF) are prominent among mechanisms that mediate cellular responses to limited oxygen but also are induced by lymphocyte activation. We now show that loss of HIF-1α or of both HIF-1α and HIF-2α in CD4⁺ T cells compromised essential functions in help during antibody responses. HIF-1α depletion from CD4⁺ T cells reduced frequencies of antigen-specific GC B cells, Tfh cells, and overall antigen-specific Ab after immunization with sheep red blood cells. Compound deficiency of HIF-1α and HIF-2α led to humoral defects after hapten-carrier immunization. Further, HIF promoted CD40L expression while restraining the FoxP3-positive CD4⁺ cells in the CXCR5⁺ follicular regulatory population. Glycolysis increases T helper cytokine expression, and HIF promoted glycolysis in T helper cells via TCR or cytokine stimulation, as well as their production of cytokines that direct antibody class switching. Indeed, IFN-γ elaboration by HIF-deficient in vivo-generated Tfh cells was impaired. Collectively, the results indicate that HIF transcription factors are vital components of the mechanisms of help during humoral responses.

Growth Factor-like Gene Regulation Is Separable from Survival and Maturation in Antibody-Secreting Cells

Recurrent mutational activation of the MAP kinase pathway in plasma cell myeloma implicates growth factor-like signaling responses in the biology of Ab-secreting cells (ASCs). Physiological ASCs survive in niche microenvironments, but how niche signals are propagated and integrated is poorly understood. In this study, we dissect such a response in human ASCs using an in vitro model. Applying time course expression data and parsimonious gene correlation network analysis (PGCNA), a new approach established by our group, we map expression changes that occur during the maturation of proliferating plasmablast to quiescent plasma cell under survival conditions including the potential niche signal TGF-β3. This analysis demonstrates a convergent pattern of differentiation, linking unfolded protein response/endoplasmic reticulum stress to secretory optimization, coordinated with cell cycle exit. TGF-β3 supports ASC survival while having a limited effect on gene expression including upregulation of CXCR4. This is associated with a significant shift in response to SDF1 in ASCs with amplified ERK1/2 activation, growth factor-like immediate early gene regulation and EGR1 protein expression. Similarly, ASCs responding to survival conditions initially induce partially overlapping sets of immediate early genes without sustaining the response. Thus, in human ASCs growth factor-like gene regulation is transiently imposed by niche signals but is not sustained during subsequent survival and maturation.

Interruption of autoimmunity for thyroid eye disease: B-cell and T-cell strategy

Recent new insights into the molecular basis of thyroid eye disease have led to the use of more specific therapies such as monoclonal antibodies This review explores the traditional immunosuppressant therapy for TED, highlighting the basis for emergent recent medications, possible treatment options and, eventually possible new general recommendation for management of TED. Data has been retrieved from the literature searching on Pubmed. Steroid therapy remains the first line therapy for moderate/severe and severe vision threatening TED The use of some traditional nonspecific immunosuppressant such as mycophenolate, cyclosporine and azathioprine seems useful in combination with steroid therapy to achieve stable results in the long term; methotrexate is useful as steroid-sparing medications and in steroid resistant or intolerant patients. In recent years, many scientific reports have showed the effectiveness of biological immunosuppressive agents in the management of TED. Etanercept, adalimumab, and tocilizumab have shown to be effective in reduction of the inflammatory signs with the possible advantage to prevent relapse of the disease. Particularly Tociliuzumab seems very effective as second line therapy, after steroid failure. Teprotumumab may control the disease activity and it seems to be very effective in preventing severity disease progression. Infliximab might be useful in severe TED with optic nerve compression resistant to steroid and decompression. Indeed, the actual incidence of adverse effects is not well assessed yet, therefore the use should be limited at those cases that really need an alternative therapy to steroid, handled by an expert multidisciplinary team.

Computationally optimized broadly reactive vaccine based upon swine H1N1 influenza hemagglutinin sequences protects against both swine and human isolated viruses

Swine H1 influenza viruses were stable within pigs for nearly 70 years until in 1998 when a classical swine virus reassorted with avian and human influenza viruses to generate the novel triple reassortant H1N1 strain that eventually led to the 2009 influenza pandemic. Previously, our group demonstrated broad protection against a panel of human H1N1 viruses using HA antigens derived by the COBRA methodology. In this report, the effectiveness of COBRA HA antigens (SW1, SW2, SW3 and SW4), which were designed using only HA sequences from swine H1N1 and H1N2 isolates, were tested in BALB/c mice. The effectiveness of these vaccines were compared to HA sequences designed using both human and swine H1 HA sequences or human only sequences. SW2 and SW4 elicited antibodies that detected the pandemic-like virus, A/California/07/2009 (CA/09), had antibodies with HAI activity against almost all the classical swine influenza viruses isolated from 1973-2015 and all of the Eurasian viruses in our panel. However, sera collected from mice vaccinated with SW2 or SW4 had HAI activity against ~25% of the human seasonal-like influenza viruses isolated from 2009-2015. In contrast, the P1 COBRA HA vaccine (derived from both swine and human HA sequences) elicited antibodies that had HAI activity against both swine and human H1 viruses and protected against CA/09 challenge, but not a human seasonal-like swine H1N2 virus challenge. However, the SW1 vaccine protected against this challenge as well as the homologous vaccine. These results support the idea that a pan-swine-human H1 influenza virus vaccine is possible.

Different frequencies of memory B-cells induced by tetanus, botulinum, and heat-labile toxin binding domains

Along with robust immunogenicity, an ideal vaccine candidate should be able to produce a long lasting protection. In this regard, the frequency of memory B-cells is possibly an important factor in memory B-cell persistency and duration of immunological memory. On this basis, binding domains of tetanus toxin (HcT), botulinum type A1 toxin (HcA), and heat-labile toxin (LTB) were selected as antigen models that induced long-term, midterm and short-term immune memory, respectively. In the present study, the frequency of total memory B-cells after immunization with HcT, HcA and LTB antigens after 90 and 180 days, and also after one booster, in 190 days, was evaluated. The results showed a significant correlation between frequency of total memory B-cells and duration of humoral immunity. Compared to other antigens, the HcT antibody titers and HcT total memory B-cell populations were greater and persistent even after 6 months. At 6 months after the final immunization, all HcT- and HcA-immunized mice survived against tetanus and botulinum toxins, and also LT toxin binding to GM1 ganglioside was blocked in LTB-immunized mice. We conclude the frequency of memory B-cells and their duration are likely a key factor for vaccine memory duration.

Non-coding Class Switch Recombination-Related Transcription in Human Normal and Pathological Immune Responses

Antibody class switch recombination (CSR) to IgG, IgA, or IgE is a hallmark of adaptive immunity, allowing antibody function diversification beyond IgM. CSR involves a deletion of the IgM/IgD constant region genes placing a new acceptor Constant gene, downstream of the VDJ_H exon. CSR depends on non-coding (CSRnc) transcription of donor I_μ and acceptor I_H exons, located 5′ upstream of each C_H coding gene. Although, our knowledge of the role of CSRnc transcription has advanced greatly, its extension and importance in healthy and diseased humans is scarce. We analyzed CSRnc transcription in 70,603 publicly available RNA-seq samples, including GTEx, TCGA, and the Sequence Read Archive using recount2, an online resource consisting of normalized RNA-seq gene and exon counts, as well as, coverage BigWig files that can be programmatically accessed through R. CSRnc transcription was validated with a qRT-PCR assay for I_μ, I_γ3, and I_γ1 in humans in response to vaccination. We mapped I_H transcription for the human IGH locus, including the less understood IGHD gene. CSRnc transcription was restricted to B cells and is widely distributed in normal adult tissues, but predominant in blood, spleen, MALT-containing tissues, visceral adipose tissue and some so-called “immune privileged” tissues. However, significant I_γ4 expression was found even in non-lymphoid fetal tissues. CSRnc expression in cancer tissues mimicked the expression of their normal counterparts, with notable pattern changes in some common cancer subsets. CSRnc transcription in tumors appears to result from tumor infiltration by B cells, since CSRnc transcription was not detected in corresponding tumor-derived immortal cell lines. Additionally, significantly increased I_δ transcription in ileal mucosa in Crohn's disease with ulceration was found. In conclusion, CSRnc transcription occurs in multiple anatomical locations beyond classical secondary lymphoid organs, representing a potentially useful marker of effector B cell responses in normal and pathological immune responses. The pattern of I_H exon expression may reveal clues of the local immune response (i.e., cytokine milieu) in health and disease. This is a great example of how the public recount2 data can be used to further our understanding of transcription, including regions outside the known transcriptome.

Lipoxin B4 Enhances Human Memory B Cell Antibody Production via Upregulating Cyclooxygenase-2 Expression

Vaccination has been the most effective way to prevent or reduce infectious diseases; examples include the eradication of smallpox and attenuation of tetanus and measles. However, there is a large segment of the population that responds poorly to vaccines, in part because they are immunocompromised because of disease, age, or pharmacologic therapy and are unable to generate long-term protection. Specialized proresolving mediators are endogenously produced lipids that have potent proresolving and anti-inflammatory activities. Lipoxin B₄ (LXB₄) is a member of the lipoxin family, with its proresolving effects shown in allergic airway inflammation. However, its effects on the adaptive immune system, especially on human B cells, are not known. In this study, we investigated the effects of LXB₄ on human B cells using cells from healthy donors and donors vaccinated against influenza virus in vitro. LXB₄ promoted IgG Ab production in memory B cells and also increased the number of IgG-secreting B cells. LXB₄ enhanced expression of two key transcription factors involved in plasma cell differentiation, BLIMP1 and XBP1. Interestingly, LXB₄ increased expression of cyclooxygenase-2 (COX2), an enzyme that is required for efficient B cell Ab production. The effects of LXB₄ are at least partially COX2-dependent as COX2 inhibitors attenuated LXB₄-stimulated BLIMP1 and Xpb-1 expression as well as IgG production. Thus, our study reveals for the first time, to our knowledge, that LXB₄ boosts memory B cell activation through COX2 and suggests that LXB₄ can serve as a new vaccine adjuvant.

Natural regulatory plasma cells

B cells can generate several types of antibody-secreting cells, including plasmablasts that divide and are short lived, as well as plasma cells that do not proliferate and can persist for extended time periods. Here, we discuss the identification of a novel subset of non-dividing plasma cells specialized in the production of interleukin(IL)-10. These cells develop at steady state, including in germ-free mice, via a mechanism dependent on the B cell receptor for antigen and possibly involving the recognition of damaged cells. They are characterized by the expression of the inhibitory receptor LAG-3, and also express CD200, PD-L1, as well as PD-L2. Their specialized epigenome allows them to produce IL-10 within hours after stimulation, which altogether qualify these cells as natural regulatory plasma cells.

Loss of CXCR3 expression on memory B cells in individuals with long-standing type 1 diabetes

AIMS/HYPOTHESIS

Islet-specific autoantibodies can predict the development of type 1 diabetes. However, it remains unclear if B cells, per se, contribute to the causal pancreatic immunopathology. We aimed to identify phenotypic signatures of disease progression among naive and memory B cell subsets in the peripheral blood of individuals with type 1 diabetes.

METHODS

A total of 69 participants were recruited across two separate cohorts, one for discovery purposes and the other for validation purposes. Each cohort comprised two groups of individuals with type 1 diabetes (one with newly diagnosed type 1 diabetes and the other with long-standing type 1 diabetes) and one group of age- and sex-matched healthy donors. The phenotypic characteristics of circulating naive and memory B cells were investigated using polychromatic flow cytometry, and serum concentrations of various chemokines and cytokines were measured using immunoassays.

RESULTS

A disease-linked phenotype was detected in individuals with long-standing type 1 diabetes, characterised by reduced C-X-C motif chemokine receptor 3 (CXCR3) expression on switched (CD27⁺IgD^-) and unswitched (CD27^intermediateIgD⁺) memory B cells. These changes were associated with raised serum concentrations of B cell activating factor and of the CXCR3 ligands, chemokine (C-X-C motif) ligand (CXCL)10 and CXCL11. A concomitant reduction in CXCR3 expression was also identified on T cells.

CONCLUSIONS/INTERPRETATION

Our data reveal a statistically robust set of abnormalities that indicate an association between type 1 diabetes and long-term dysregulation of a chemokine ligand/receptor system that controls B cell migration.

Toll-like receptor 4 signalling regulates antibody response to adenoviral vector-based vaccines by imprinting germinal centre quality

Adenoviral vectors (AdV) are considered promising candidates for vaccine applications. A prominent group of Toll-like receptors (TLRs) participate in the adenovirus-induced adaptive immune response, yet there is little information regarding the role of TLR4 in AdV-induced immune responses in recent literature. We investigated the function of TLR4 in both adaptive and innate immune responses to an AdV-based anthrax vaccine. By immunizing wild-type and TLR4 knockout (TLR4-KO) mice, we revealed the requirement of TLR4 in AdV-induced innate responses. We also showed that TLR4 functions are required for germinal centre responses in immunized mice, as expression of the apoptosis-related marker Fas was down-regulated on germinal centre B cells from TLR4-KO mice. Likewise, decreased expression of inducible costimulator on follicular T helper cells was observed in immunized TLR4-KO mice. Moreover, a potent protective antigen-specific humoral immune response was mimicked using an adjuvant system containing the TLR4 agonist monophosphoryl lipid A. Overall, our findings showed that very rapid antigen-specific antibody production is correlated with the TLR4-imprinted germinal centre response to AdV-based vaccine. These results provide additional evidence for the use of the AdV and a TLR agonist to induce humoral responses. Our findings offer new insights into rational vaccine design.

Naive B Cells with High-Avidity Germline-Encoded Antigen Receptors Produce Persistent IgM+ and Transient IgG+ Memory B Cells

Although immune memory often lasts for life, this is not the case for certain vaccines in some individuals. We sought a mechanism for this phenomenon by studying B cell responses to phycoerythrin (PE). PE immunization of mouse strains with Igh^b immunoglobulin (Ig) variable heavy chain (V_H) genes elicited affinity-matured switched Ig memory B cells that declined with time, while the comparable population from an Igh^a strain was numerically stable. Igh^b strains had larger numbers of PE-specific naive B cells and generated smaller germinal center responses and larger numbers of IgM memory cells than the Igh^a strain. The properties of PE-specific B cells in Igh^b mice correlated with usage of a single V_H that afforded high-affinity PE binding in its germline form. These results suggest that some individuals may be genetically predisposed to generate non-canonical memory B cell responses to certain antigens because of avid antigen binding via germline-encoded V_H elements.

Humoral immune responses to infection: common mechanisms and unique strategies to combat pathogen immune evasion tactics

Humoral immune responses are crucial for protection against invading pathogens and are the underlying mechanism of protection for most successful vaccines. Our understanding of how humoral immunity develops is largely based on animal models utilizing experimental immunization systems. While these studies have made enormous progress for the field and have defined many of the fundamental principles of B cell differentiation and function, we are only now beginning to appreciate the complexities of humoral immune responses induced by infection. Co-evolution of the adaptive immune system and the pathogenic world has created a diverse array of B cell responses to infections, with both shared and unique strategies. In this review, we consider the common mechanisms that regulate the development of humoral immune responses during infection and highlight recent findings demonstrating the evolution of unique strategies used by either host or pathogen for survival.

Acquired thrombotic thrombocytopenic purpura

The von Willebrand factor (VWF)-cleaving metalloprotease, ADAMTS13 (a disintegrin and metalloprotease with thrombospondin type 1 motifs-13) is the only known target of the dysregulated immune response in acquired TTP. Autoantibodies to ADAMTS13 either neutralize its activity or accelerate its clearance, thereby causing a severe deficiency of ADAMTS13 in plasma. As a consequence, size regulation of VWF is impaired and the persistence of ultra-large VWF (ULVWF) multimers facilitates micro vascular platelet aggregation causing microangiopathic haemolytic anaemia and ischaemic organ damage. Autoimmune TTP although a rare disease with an annual incidence of 1.72 cases has a mortality rate of 20% even with adequate therapy.

We describe the mechanisms involved in ADAMTS13 autoimmunity with a focus on the role of B- and T-cells in the pathogenesis of this disorder. We discuss the potential translation of recent experimental findings into future therapeutic concepts for the treatment of acquired TTP.

Reduced Immunocompetent B Cells and Increased Secondary Infection in Elderly Patients With Severe Sepsis

Lymphocyte exhaustion was recently recognized as a mechanism of immunosuppression in sepsis. While B cells are known to play pivotal roles in bacterial infection and sepsis, changes in B-cell-mediated humoral immunity have not been evaluated in critically ill septic patients. We aimed to investigate changes in humoral immunity caused by defective B-cell function during severe sepsis. Thirty-three severe sepsis patients and 44 healthy subjects were prospectively enrolled. Blood was collected from patients within 72 h of and 8 to 11 h after sepsis onset to measure B-cell subtypes, serum immunoglobulin M concentration, and CpG-B oligodeoxynucleotide-induced immunoglobulin M (IgM) production ex vivo. Participants were divided into two age groups: adults (18-64 years) and elderly (≥65 years). The fraction of CD21 exhausted B cells in acute sepsis patients (3.18%) was higher than that observed in healthy donors (0.77%, respectively, P <0.01). Significantly, serum IgM in elderly septic patients (≥65 years) was negatively correlated with acute physiology and chronic health evaluation II score (r = -0.57, P <0.05). Consistently, in B cells stimulated ex vivo, both aging and sepsis induced significant reductions in supernatant IgM (P <0.01). This finding was clinically relevant, as elderly patients with decreased IgM production might be more susceptible to infection by Gram-negative bacteria and fungi. Reduced immunocompetent B cells may be related to increased secondary infection after sepsis, especially in the elderly. Finally, impaired humoral immunity with increased CD21 exhausted B cells and insufficient immunoglobulin M production may be a critical immunological change in sepsis.

Quantification of plasma cell dynamics using mathematical modelling

Plasma cells (PCs) are the main antibody-producing cells in humans. They are long-lived so that specific antibodies against either pathogens or vaccines are produced for decades. PC longevity is attributed to specific areas within the bone marrow micro-environment, the so-called 'niche', providing the cells with required growth and survival factors. With antigen encounters, e.g. infection or vaccination, new PCs are generated and home to the bone marrow where they compete with resident PCs for the niche. We propose a parametrized mathematical model describing healthy PC dynamics in the bone marrow. The model accounts for competition for the niche between newly produced PCs owing to vaccination and resident PCs. Mathematical analysis and numerical simulations of the model allow explanation of the recovery of PC homoeostasis after a vaccine-induced perturbation, and the fraction of vaccine-specific PCs inside the niche. The model enables quantification of the niche-related dynamics of PCs, i.e. the duration of PC transition into the niche and the impact of different rates for PC transitions into and out of the niche on the observed cell dynamics. Ultimately, it provides a potential basis for further investigations in health and disease.

Epstein-Barr Virus, but Not Cytomegalovirus, Latency Accelerates the Decay of Childhood Measles and Rubella Vaccine Responses-A 10-Year Follow-up of a Swedish Birth Cohort

BACKGROUND

Epstein-Barr virus (EBV) and cytomegalovirus (CMV) are ubiquitous and persistent herpesviruses commonly acquired during childhood. Both viruses have a significant impact on the immune system, especially through mediating the establishment of cellular immunity, which keeps these viruses under control for life. Far less is known about how these viruses influence B-cell responses.

OBJECTIVES

To evaluate the impact of latent EBV and CMV infection on rubella- and measles-specific antibody responses as well as on the B-cell compartment in a prospective birth cohort followed during the first 10 years of life.

METHODS

IgG titers against rubella and measles vaccines were measured in plasma obtained from the same donors at 2, 5, and 10 years of age. Peripheral B-cell subsets were evaluated ex vivo at 2 and 5 years of age. Factors related to optimal B-cell responses including IL-21 and CXCL13 levels in plasma were measured at all-time points.

RESULTS

EBV carriage in the absence of CMV associated with an accelerated decline of rubella and measles-specific IgG levels (p = 0.003 and p = 0.019, respectively, linear mixed model analysis), while CMV carriage in the absence of EBV associated with delayed IgG decay over time for rubella (p = 0.034). At 5 years of age, EBV but not CMV latency associated with a lower percentage of plasmablasts, but higher IL-21 levels in the circulation.

CONCLUSION

Our findings suggest that EBV carriage in the absence of CMV influences the B-cell compartment and the dynamics of antibody responses over time during steady state in the otherwise healthy host.

Elicitation of Protective Antibodies against a Broad Panel of H1N1 Viruses in Ferrets Preimmune to Historical H1N1 Influenza Viruses

Most preclinical animal studies test influenza vaccines in immunologically naive animal models, even though the results of vaccination may not accurately reflect the effectiveness of vaccine candidates in humans that have preexisting immunity to influenza. In this study, novel, broadly reactive influenza vaccine candidates were assessed in preimmune ferrets. These animals were infected with different H1N1 isolates before being vaccinated or infected with another influenza virus. Previously, our group has described the design and characterization of computationally optimized broadly reactive hemagglutinin (HA) antigens (COBRA) for H1N1 isolates. Vaccinating ferrets with virus-like particle (VLP) vaccines expressing COBRA HA proteins elicited antibodies with hemagglutination inhibition (HAI) activity against more H1N1 viruses in the panel than VLP vaccines expressing wild-type HA proteins. Specifically, ferrets infected with the 1986 virus and vaccinated with a single dose of the COBRA HA VLP vaccines elicited antibodies with HAI activity against 11 to 14 of the 15 H1N1 viruses isolated between 1934 and 2013. A subset of ferrets was infected with influenza viruses expressing the COBRA HA antigens. These COBRA preimmune ferrets had superior breadth of HAI activity after vaccination with COBRA HA VLP vaccines than COBRA preimmune ferrets vaccinated with VLP vaccines expressing wild-type HA proteins. Overall, priming naive ferrets with COBRA HA based viruses or using COBRA HA based vaccines to boost preexisting antibodies induced by wild-type H1N1 viruses, COBRA HA antigens elicited sera with the broadest HAI reactivity against multiple antigenic H1N1 viral variants. This is the first report demonstrating the effectiveness of a broadly reactive or universal influenza vaccine in a preimmune ferret model.IMPORTANCE Currently, many groups are testing influenza vaccine candidates to meet the challenge of developing a vaccine that elicits broadly reactive and long-lasting protective immune responses. The goal of these vaccines is to stimulate immune responses that react against most, if not all, circulating influenza strains, over a long period of time in all populations of people. Commonly, these experimental vaccines are tested in naive animal models that do not have anti-influenza immune responses; however, humans have preexisting immunity to influenza viral antigens, particularly antibodies to the HA and NA glycoproteins. Therefore, this study investigated how preexisting antibodies to historical influenza viruses influenced HAI-specific antibodies and protective efficacy using a broadly protective vaccine candidate.

Detection, phenotyping and quantification of dengue virus-specific B cells using fluorescent probes

Dengue viruses are some of the most important mosquito-borne pathogens worldwide. They cause illness in 50-100 million individuals per year and have a significant global health impact in low- and middle-income countries. It is important to improve our understanding of the humoral response to dengue virus, as antibodies (Abs) are associated with protection from or susceptibility to severe dengue disease. In recent years, significant advances have been made toward identifying Ab targets and evaluating the functional properties of Abs. However, much less is known about the cellular source of Abs, B cells, in part because the reagents to phenotype and characterize antigen-specific B cells have been challenging to develop. Here, we discuss our recent experience with developing and using fluorescent viruses to probe the B cell response to dengue virus. We present the strengths and weaknesses of flow cytometric analysis of antigen-specific B cells and discuss the use of these probes to phenotype and characterize specific B cells during and after natural infection and in ongoing dengue vaccine trials.

The chronically inflamed central nervous system provides niches for long-lived plasma cells

Although oligoclonal bands in the cerebrospinal fluid have been a hallmark of multiple sclerosis diagnosis for over three decades, the role of antibody-secreting cells in multiple sclerosis remains unclear. T and B cells are critical for multiple sclerosis pathogenesis, but increasing evidence suggests that plasma cells also contribute, through secretion of autoantibodies. Long-lived plasma cells are known to drive various chronic inflammatory conditions as e.g. systemic lupus erythematosus, however, to what extent they are present in autoimmune central nervous system inflammation has not yet been investigated. In brain biopsies from multiple sclerosis patients and other neurological diseases, we could detect non-proliferating plasma cells (CD138⁺Ki67⁻) in the parenchyma. Based on this finding, we hypothesized that long-lived plasma cells can persist in the central nervous system (CNS). In order to test this hypothesis, we adapted the multiple sclerosis mouse model experimental autoimmune encephalomyelitis to generate a B cell memory response. Plasma cells were found in the meninges and the parenchyma of the inflamed spinal cord, surrounded by tissue areas resembling survival niches for these cells, characterized by an up-regulation of chemokines (CXCL12), adhesion molecules (VCAM-1) and survival factors (APRIL and BAFF). In order to determine the lifetime of plasma cells in the chronically inflamed CNS, we labeled the DNA of proliferating cells with 5-ethynyl-2′-deoxyuridine (EdU). Up to five weeks later, we could detect EdU⁺ long-lived plasma cells in the murine CNS. To our knowledge, this is the first study describing non-proliferating plasma cells directly in the target tissue of a chronic inflammation in humans, as well as the first evidence demonstrating the ability of plasma cells to persist in the CNS, and the ability of the chronically inflamed CNS tissue to promote this persistence. Hence, our results suggest that the CNS provides survival niches for long-lived plasma cells, similar to the niches found in other organs. Targeting these cells in the CNS offers new perspectives for treatment of chronic autoimmune neuroinflammatory diseases, especially in patients who do not respond to conventional therapies.

Isolation and Characterization of Antigen-Specific Plasmablasts Using a Novel Flow Cytometry-Based Ig Capture Assay

We report the development of a novel flow cytometry-based Ig capture assay (ICA) for the identification and sorting of individual Ab-secreting cells based on their Ag reactivity. The ICA represents a fast and versatile tool for single-cell sorting of peripheral plasmablasts, streamlining subsequent Ab analysis, and cloning. We demonstrate the utility of the assay by isolating Ag-reactive plasmablasts from cryopreserved PBMC obtained from volunteers vaccinated with a recombinant HIV envelope protein. To show the specificity of the ICA, we produced Ag-specific Abs from these cells and subsequently verified their Ag reactivity via ELISA. Furthermore, we used the ICA to track Ag-specific plasmablast responses in HIV-vaccine recipients over a period of 42 d and performed a head-to-head comparison with a conventional B cell ELISpot. Results were highly comparable, highlighting that this assay is a viable alternative for monitoring Ag-specific plasmablast responses at early time points after infection or vaccination. The ICA provides important added benefits in that phenotypic information can be obtained from the identified Ag-specific cells that can then be captured for downstream applications such as B cell sequencing and/or Ab cloning. We envisage the ICA as being a useful tool in Ab repertoire analysis for future clinical trials.

Kv1.3 Channel Blockade Modulates the Effector Function of B Cells in Granulomatosis with Polyangiitis

B cells are central to the pathogenesis of granulomatosis with polyangiitis (GPA), exhibiting both (auto)antibody-dependent and -independent properties. Class-switched memory B cells in particular are a major source of pathogenic autoantibodies. These cells are characterized by high expression levels of Kv1.3 potassium channels, which may offer therapeutic potential for Kv1.3 blockade. In this study, we investigated the effect of the highly potent Kv1.3 blocker ShK-186 on B cell properties in GPA in vitro. Circulating B cell subsets were determined from 33 GPA patients and 17 healthy controls (HCs). Peripheral blood mononuclear cells (PBMCs) from GPA patients, and HCs were stimulated in vitro in the presence and absence of ShK-186. The production of total and antineutrophil cytoplasmic antibodies targeting proteinase 3 (PR3-ANCA) IgG was analyzed by enzyme-linked immunosorbent assay and Phadia EliA, respectively. In addition, effects of ShK-186 on B cell proliferation and cytokine production were determined by flow cytometry. The frequency of circulating switched and unswitched memory B cells was decreased in GPA patients as compared to HC. ShK-186 suppressed the production of both total and PR3-ANCA IgG in stimulated PBMCs. A strong decrease in production of tumor necrosis factor alpha (TNFα), interleukin (IL)-2, and interferon gamma was observed upon ShK-186 treatment, while effects on IL-10 production were less pronounced. As such, ShK-186 modulated the TNFα/IL-10 ratio among B cells, resulting in a relative increase in the regulatory B cell pool. ShK-186 modulates the effector functions of B cells in vitro by decreasing autoantibody and pro-inflammatory cytokine production. Kv1.3 channel blockade may hold promise as a novel therapeutic strategy in GPA and other B cell-mediated autoimmune disorders.

The transcriptional profiling of human in vivo-generated plasma cells identifies selective imbalances in monoclonal gammopathies

Plasma cells (PC) represent the heterogeneous final stage of the B cells (BC) differentiation process. To characterize the transition of BC into PC, transcriptomes from human naïve BC were compared to those of three functionally-different subsets of human in vivo-generated PC: i) tonsil PC, mainly consisting of early PC; ii) PC released to the blood after a potent booster-immunization (mostly cycling plasmablasts); and, iii) bone marrow CD138⁺ PC that represent highly mature PC and include the long-lived PC compartment. This transcriptional transition involves subsets of genes related to key processes for PC maturation: the already known protein processing, apoptosis and homeostasis, and of new discovery including histones, macromolecule assembly, zinc-finger transcription factors and neuromodulation. This human PC signature is partially reproduced in vitro and is conserved in mouse. Moreover, the present study identifies genes that define PC subtypes (e.g., proliferation-associated genes for circulating PC and transcriptional-related genes for tonsil and bone marrow PC) and proposes some putative transcriptional regulators of the human PC signatures (e.g., OCT/POU, XBP1/CREB, E2F, among others). Finally, we also identified a restricted imbalance of the present PC transcriptional program in monoclonal gammopathies that correlated with PC malignancy.

Peripheral Ulcerative Keratitis Associated with Autoimmune Disease: Pathogenesis and Treatment

Peripheral ulcerative keratitis (PUK) is type of crescent-shaped inflammatory damage that occurs in the limbal region of the cornea. PUK is always combined with an epithelial defect and the destruction of the peripheral corneal stroma. PUK may have a connection to systemic conditions, such as long-standing rheumatoid arthritis (RA), systemic lupus erythematosus (SLE), Wegener granulomatosis (WG), relapsing polychondritis, classic polyarteritis nodosa and its variants, microscopic polyangiitis, and Churg-Strauss syndrome. However, the most common connection is with RA, which is also the focus of this review. The pathogenesis of PUK is still unclear. It is thought that circulating immune complexes and cytokines exert an important influence on the progression of this syndrome. Treatment is applied to inhibit certain aspects of PUK pathogenesis.

Type I interferon as a biomarker in autoimmunity and viral infection: a leukocyte subset-specific analysis unveils hidden diagnostic options

Interferon alpha and its surrogates, including IP-10 and SIGLEC1, paralleled changes of disease activity in systemic lupus erythematosus (SLE). However, the whole blood interferon signature (WBIFNS)-the current standard for type I IFN assessment in SLE-does not correlate with SLE disease activity in individual patients over time. The underlying causes for this apparent contradiction have not been convincingly demonstrated. Using a multicenter dataset of gene expression data from leukocyte subsets in SLE, we identify distinctive subset-specific contributions to the WBIFNS. In a subsequent analysis, the effects of type I interferon on cellular blood composition in patients with SLE and hepatitis B were also studied over time. We found that type I interferon mediates significant alterations in whole blood composition, including a neutropenia and relative lymphocytosis. Given different effects of type 1 interferon on different leukocyte subsets, these shifts confound measurement of a type 1 interferon signature in whole blood. To minimize and overcome these limitations of the WBIFNS, we suggest to measure IFN-induced transcripts or proteins in a specific leukocyte subset to improve clinical impact of interferon biomarkers.

KEY MESSAGES

Myeloid cells contribute more to the WBIFNS in SLE than their lymphocytic counterpart. Very similar leukocyte subsets reveal distinctive IFN signatures. IFN alpha mixes up composition of blood and leads to a preferential neutropenia, yielding relative lymphocytosis.

Protein-Free Hapten-Carbon Nanotube Constructs Induce the Secondary Immune Response

Carbon nanotubes are novel technological tools with multiple applications. The interaction between such nanoparticles and living organisms is nowadays a matter of keen research by academic and private institutions. In this study, carbon nanotube constructs were investigated as delivery vehicles for immunostimulation and induction of the secondary immune response to a small organic molecule, namely, a hapten. Two types of nanoconstructs were prepared: on one hand, carbon nanotubes carrying a protein bioconjugate of a hapten covalently linked to the carbon surface, and on the other hand, covalent carbon nanotube constructs of the same model chemical compound without the carrier protein. Nanotube vehicles carrying a hapten-protein bioconjugate were demonstrated to stimulate the immune system and to induce a strong primary immune response against the hapten with as low as 0.1 μg of the model chemical. The influence of the different elements of those nanoconstructs over the immune response was investigated to better understand the molecular mechanisms that are involved. As expected, the presence of the carrier protein was shown to be necessary in order to trigger the immune response. Interestingly, we found that a remarkable secondary immune response to the model organic compound occurred in the absence of a carrier protein. Additionally, a satisfactory adjuvant effect of carbon nanotubes was observed and a potent immune response was elicited without employing an oil-based adjuvant.

Early Emergence of CD19-Negative Human Antibody-Secreting Cells at the Plasmablast to Plasma Cell Transition

Long-lived human plasma cells (PCs) play central roles in immunity and autoimmunity and are enriched among the subpopulation of CD19neg human PCs. However, whether human CD19neg PCs are necessarily aged cells that have gradually lost CD19 expression is not known. Assessing peripheral blood samples at steady-state and during the acute response to influenza vaccination in healthy donors, we identify the presence of phenotypic CD19neg plasmablasts, the proliferative precursor state to mature PCs, and demonstrate by ELISPOT that these are Ab-secreting cells (ASCs). During the acute response to influenza vaccination, CD19pos, CD19low, and CD19neg ASCs secrete vaccine-specific Abs and show linked IGHV repertoires. To address precursor/product relationships, we use in vitro models that mimic T-dependent and T-independent differentiation, finding that the CD19neg state can be established at the plasmablast to PC transition, that CD19neg PCs increase as a percentage of surviving PCs in vitro, and that CD19neg and CD19pos PCs can be maintained independently. These data provide proof-of-principle for the view that newly generated ASCs can acquire a mature PC phenotype that is accompanied by loss of CD19 expression at an early stage of differentiation and that aging is not an obligate requirement for a CD19neg state to be established.

Protective and pathogenic memory plasma cells

The immune system can be divided into two major parts: innate and adaptive immunity. Adaptive immunity is characterized by its major cellular players: the B and T cells. B cells will, in the context of an immune reaction, differentiate into plasma cells. These plasma cells produce antibodies, which are secreted. Antibodies are characterized by their specificity against a selected antigen and by their isotype. The isotype changes with the duration or phase of the immune reaction. Early immune reactions are usually characterized by the predominant production of IgM antibodies. With the persistence of the immune reaction immunoglobulin class switch occurs and plasma cells will produce IgG, IgE or IgA-antibodies (Radbruch et al., 2006) [1].

Memory B cell response to a PCV-13 booster in 3.5year old children primed with either PCV-7 or PCV-13

Pneumococcal protein-polysaccharide conjugate vaccines provide direct protection against Streptococcus pneumoniae through the induction of persistent anti-polysaccharide antibodies, and by priming for a rapid secondary antibody response. Memory B cells (B_MEM) generated during an initial immune response are responsible for both the more rapid and quantitatively greater secondary antibody response and are also thought to contribute to the ongoing production of plasma cells providing long-term antibody persistence. We recruited 3.5-year-old children who had participated in a previous clinical trial comparing infant immunization with either a 7-valent (PCV-7) or a 13-valent pneumococcal conjugate vaccine (PCV-13) to investigate whether prior priming with pneumococcal antigens influences B_MEM responses. Blood was taken before and 1month after a PCV-13 booster. B_MEM were quantified using a cultured ELISpot assay for pneumococcal serotypes 1, 3, 4, 14, 19A, 23F, and with diphtheria and tetanus toxoid as controls, and then correlated with serotype-specific IgG concentrations and opsonophagocytic activity (OPA) titers. In total, blood samples from 62 participants were available for analysis. Serotype-specific B_MEM frequencies were generally low at baseline (before boost) although for serotypes 14 and 3, they were significantly higher in children primed with PCV-13 than PCV-7 primed children. Following the PCV-13 booster, B_MEM frequencies increased and were not different between the groups for all serotypes. A strong inverse correlation was found between antibody concentrations and OPA titers at baseline and B_MEM following booster vaccination for serotype 3 but not for other serotypes suggesting that, for this serotype, pre-existing serotype-specific antibodies may inhibit B_MEM formation in response to vaccination. Clinicaltrials.gov registration number: NCT01095471.

Elementary immunology: Na+ as a regulator of immunity

The skin can serve as an interstitial Na+ reservoir. Local tissue Na+ accumulation increases with age, inflammation and infection. This increased local Na+ availability favors pro-inflammatory immune cell function and dampens their anti-inflammatory capacity. In this review, we summarize available data on how NaCl affects various immune cells. We particularly focus on how salt promotes pro-inflammatory macrophage and T cell function and simultaneously curtails their regulatory and anti-inflammatory potential. Overall, these findings demonstrate that local Na+ availability is a promising novel regulator of immunity. Hence, the modulation of tissue Na+ levels bears broad therapeutic potential: increasing local Na+ availability may help in treating infections, while lowering tissue Na+ levels may be used to treat, for example, autoimmune and cardiovascular diseases.

Methotrexate reduces vaccine-specific immunoglobulin levels but not numbers of circulating antibody-producing B cells in rheumatoid arthritis after vaccination with a conjugate pneumococcal vaccine

BACKGROUND

Treatment with methotrexate (MTX) in patients with rheumatoid arthritis (RA) leads to decreased total immunoglobulin (Ig) levels and impairs vaccine-specific IgG antibody levels following pneumococcal vaccination. The mechanisms by which MTX exerts these effects in RA are unknown. We aimed to evaluate whether MTX reduces vaccine-specific serum Ig levels and their functionality in RA patients following vaccination with pneumococcal conjugate vaccine, and if numbers of antigen-specific circulating plasmablasts are affected.

METHODS

Ten patients with RA on MTX and 10 RA patients without disease modifying anti-rheumatic drug (DMARD) were immunized with a dose 13-valent pneumococcal conjugate vaccine (Prevenar13). Circulating plasmablasts producing total IgG and IgA as well as specific IgG and IgA against two pneumococcal capsular serotypes (6B and 23F) were enumerated using ELISPOT 6days after vaccination. IgG levels against both these serotypes were determined with ELISA before and 4-6weeks after vaccination. Positive antibody response was defined as ⩾2-fold increase of pre-vaccination antibody levels. The functionality of vaccine specific antibodies to serotype 23F was evaluated by measuring their ability to opsonize bacteria using opsonophagocytic assay (OPA) in 4 randomly chosen RA patients on MTX and 4 RA patients without DMARD.

RESULTS

After vaccination, RA patients on MTX showed significant increase in pre- to postvaccination antibody levels for 6B (p<0.05), while patients without DMARD had significant increases for both 6B and 23F (p<0.05 and p<0.01, respectively). Only 10% of RA on MTX and 40% of RA patients without DMARD showed positive post-vaccination antibody responses for both serotypes. Increased opsonizing ability after vaccination was detected in 1 of 4 RA patients on MTX and 3 of 4 patients on RA without DMARD. However, numbers of circulating total and vaccine-specific IgG- or IgA-producing plasmablasts did not differ between RA patients with or without MTX.

CONCLUSIONS

MTX treatment in RA leads to reduced vaccine-specific antibody responses and their functionality compared to untreated RA following pneumococcal vaccination using polysaccharide-protein conjugate vaccine. However, since there was no reduction in numbers of circulating total or vaccine-specific antibody-producing plasmablasts after vaccination this effect is probably not due to reduced activation of B cells in lymphoid tissue.

CLINICAL TRIAL REGISTRATION

NCT02240888.

Neutrophils releasing IL-17A into NETs are essential to plasma cell differentiation in inflamed tissue dependent on IL-1R

Interleukin (IL) 17A in chronic inflammation is also produced by innate immune cells as neutrophils. Mice with chronic humoral response induced by venom of Thalassophryne nattereri (VTn) proved to be a good tool for evaluating the impact of IL-17A on the development of long-lived plasma cells in the inflamed peritoneal cavity. Here, we report that VTn induces IL-17A production by neutrophils accumulating in the peritoneal cavity and triggers the extrusion of IL-17A along with neutrophil extracellular traps (NETs). Neutrophil depletion reduced the number of IL17A-producing cells in VTn-immunized mice and blocked the differentiation of long-lived plasma cells. Specific antibody production and survival of long-lived plasma cells was ablated in VTn-immunized mice deficient in CD4, while CD28 signaling had the opposite effect on differentiation of long-lived plasma cells. Further, maturation of long-lived plasma cells in inflamed peritoneal cavity was IL-1R1 and COX-2 dependent. Finally, when both the Raf-MEK-ERK pathway and the IL-17A or IL-1R1 activities were blocked, neutrophils were unable to promote the differentiation of memory B cells into long-lived plasma cells, confirming the essential role of neutrophils and IL-17A along with NETs in an IL-1/IL-1R-dependent manner as the novel helping partner for plasma cell differentiation in chronically inflamed tissues.

Plasmablasts During Acute Dengue Infection Represent a Small Subset of a Broader Virus-specific Memory B Cell Pool

Dengue is endemic in tropical countries worldwide and the four dengue virus serotypes often co-circulate. Infection with one serotype results in high titers of cross-reactive antibodies produced by plasmablasts, protecting temporarily against all serotypes, but impairing protective immunity in subsequent infections. To understand the development of these plasmablasts, we analyzed virus-specific B cell properties in patients during acute disease and at convalescence. Plasmablasts were unrelated to classical memory cells expanding in the blood during early recovery. We propose that only a small subset of memory B cells is activated as plasmablasts during repeat infection and that plasmablast responses are not representative of the memory B cell repertoire after dengue infection.

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Antibody sequences and functions were analyzed in longitudinal acute and convalescent samples from dengue patients

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Plasmablast antibodies were virus glycoprotein-specific whereas memory B cell-derived antibodies bound to more viral proteins

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plasmablasts seem to be activated from only a small subset of memory B cells

Antibody-mediated immune memory is orchestrated by various B cell types that are relevant during different phases after an infection. Antibody-secreting cells or so-called plasmablasts are generated from activated specific memory B cell a few days after re-infection. However, little in known whether the antibodies produced by these plasmablasts are relevant for protection in humans and whether the parent memory B cells are further maintained in the memory pool, possibly as affinity-matured versions of the original clones. This is important in the context of vaccination since the repertoires of individual B cell subsets could represent biomarkers to assess efficacy and long-term protection. In addition, the generation of “protective” B cell subsets could potentially be influenced by vaccine design and by the use of adjuvants.

We studied the relationship of plasmablasts and memory B cells in longitudinal blood samples from dengue patients. Dengue virus (DENV) has four serotypes and pre-existing antibodies can be cross-protective or can enhance disease after a heterologous infection via Fc-gamma-receptor-mediated uptake of virus-antibody complexes. B cell memory can therefore be both beneficial and detrimental. Here we studied plasmablasts and DENV-specific memory B cells and their relationship and protective potential by assessing antibody sequences and monoclonal antibodies. We found that both populations produced largely serotype cross-neutralizing antibodies, whereas more plasmablast antibodies were neutralizing. Few plasmablast clones could be found in the memory pool, suggesting that only a subset of memory B cells is activated during acute disease and that a separate repertoire of cells is retained as longer-term memory. In this study we started to dissect the complexity of B cell immune memory to dengue infection and the finding can inform further investigations into which immune cell subsets are disease-enhancing after a heterologous infection.

Distinct Differentiation Programs Triggered by IL-6 and LPS in Teleost IgM(+) B Cells in The Absence of Germinal Centers

Although originally identified as a B cell differentiation factor, it is now known that mammalian interleukin-6 (IL-6) only regulates B cells committed to plasma cells in response to T-dependent (TD) antigens within germinal centers (GCs). Even though adaptive immunity is present in teleost fish, these species lack lymph nodes and GCs. Thus, the aim of the present study was to establish the role of trout IL-6 on B cells, comparing its effects to those induced by bacterial lipopolysaccharide (LPS). We demonstrate that the effects of teleost IL-6 on naïve spleen B cells include proliferation, activation of NF-κB, increased IgM secretion, up-regulation of Blimp1 transcription and decreased MHC-II surface expression that point to trout IL-6 as a differentiation factor for IgM antibody-secreting cells (ASCs). However, LPS induced the secretion of IgM without up-regulating Blimp1, driving the cells towards an intermediate activation state in which antigen presenting mechanisms are elicited together with antibody secretion and expression of pro-inflammatory genes. Our results reveal that, in trout, IL-6 is a differentiation factor for B cells, stimulating IgM responses in the absence of follicular structures, and suggest that it was after follicular structures appeared that this cytokine evolved to modulate TD responses within the GC.

Antibody-secreting cells in respiratory tract tissues in the absence of eosinophils as supportive partners

Antibody-secreting cells (ASCs) in respiratory tract tissues provide a first line of defense against invading pathogens. These cells often secrete IgA that is efficiently transcytosed across epithelial barriers into the airway lumen where pathogens can be blocked at their point of entry. Previous literature has reported that in the bone marrow, eosinophils are required for the maintenance of ASCs, and that eosinophils co-localize with ASCs as nearest neighbors. To determine if these rules similarly apply to the maintenance of ASCs in respiratory tract tissues, we evaluated virus-specific responses 1 month and 4 months following an intranasal virus infection of eosinophil-null (∆dblGATA-1) mice. Results showed that ASCs were fractionally reduced, but were nonetheless observed in respiratory tract tissues in the absence of eosinophils. Virus-specific antibodies were similarly observed in the airways of eosinophil-deficient mice. Respiratory tract ASCs were also present in mice lacking neutrophils (Mcl1^∆M). The staining of tissue sections from the upper respiratory tract of wild-type mice following viral infections demonstrated that virus-specific ASCs were most frequently situated adjacent to epithelial cells rather than eosinophils or neutrophils. Taken together, these data emphasize that rules for cell maintenance are not absolute and that ASCs can survive in the respiratory tract without eosinophils or neutrophils as their nearest neighbors.

The ginsenoside metabolite compound K exerts its anti-inflammatory activity by downregulating memory B cell in adjuvant-induced arthritis

CONTEXT

Compound K (CK, 20-O-d-glucopyranosyl-20(S)-protopanaxadiol), a novel ginsenoside metabolite, is structurally a member of the dammarane-type triterpene saponins. Several studies have identified the anti-inflammatory activity of CK. Our previous study demonstrated that CK exerted its anti-inflammatory effect via inhibition of abnormal activation and differentiation of T cells. However, its mechanism of action on B cells remains unclear.

OBJECTIVE

The objective of this study is to investigate the effect and underlying mechanisms of CK's effects on memory B cells in the setting of adjuvant-arthritis (AA).

MATERIALS AND METHODS

Complete Freund's adjuvant was used to induce AA in rats. Rats were administered, either CK (10, 40, and 160 mg/kg), once daily for 15 d, or methotrexate (MTX; 0.5 mg/kg) once every 3 d, for a total of six times. To evaluate the anti-inflammatory effect of CK, a global assessment and a swollen joint count of AA rats were performed every 3 d. Spleen index and histopathology were examined. Subsets of B cells including CD45R(+)IgM(+) (total B cells) and CD45R(+)CD27(+) (memory B cells) and expression of CD40 and CD40L were assayed by flow cytometry.

RESULTS

Compared with the AA rats, global assessment scores and swollen joint counts were significantly lower in the treated groups received CK (40 and 160 mg/kg; p < 0.05 and p < 0.01, respectively). CK (40 and 160 mg/kg) decreased the spleen index (p < 0.01), and alleviated hyperplasia of lymph nodes (p < 0.05 and p < 0.01, respectively) and marginal zone (p < 0.05) in the spleen. In addition, CK (40 and 160 mg/kg) suppressed memory B cell subsets (p < 0.05), and suppressed CD40L expression on T cells and CD40 expression on B cells (p < 0.05 and p < 0.01, respectively).

DISCUSSION AND CONCLUSION

This study demonstrated that CK downregulated memory B cells in AA rats, and this down-regulation may be T-cell dependent.

A comparison of B cell subsets in primary immune deficiencies that progress with antibody deficiency and age-matched healthy children

BACKGROUND

The objective of this study was to examine the B lymphocyte subsets in primary immunodeficiency that progress with antibody deficiency.

METHODS

The patients' naive, memory, class-switched memory and non-switched memory B cells were compared with those of healthy individuals of matching ages using flow cytometry.

RESULTS

A total of 67 patients with antibody deficiency and 28 healthy children of matching ages were included in the study. The median age of the patients was six years (min-max: 1-24) and 40 (59.7%) were male. The median age of the healthy controls was again six years (min-max: 1-17) and 12 (42.8%) were male. Patients with common variable immunodeficiency had higher relative counts of naive cells when compared with the control group; however, they were found to have lower relative counts of memory, relative and absolute counts of non-switched and relative counts of switched B lymphocytes (p=0.001, 0.023, 0.003-0.003, 0.001, respectively). In patients with selective IgA deficiency, similar to patients with common variable immunodeficiency, the relative counts of naive cells were found to be higher, while the relative counts of memory and relative and absolute counts of non-switched B lymphocytes were found to be lower when compared with the control group (p=0.011, 0.032, 0.006-0.009, respectively). Although patients with selective IgM deficiency had higher relative counts of naive B cells when compared with the control group, they had lower relative and absolute counts of non-switched B lymphocytes (p=0.008-0.016).

CONCLUSIONS

The B lymphocyte subsets of patients with selective IgA deficiency are largely similar to those of patients with common variable immunodeficiency. Both illness groups exhibit low levels of memory B cells.

Long-lived antigen-induced IgM plasma cells demonstrate somatic mutations and contribute to long-term protection

Long-lived plasma cells are critical to humoral immunity as a lifelong source of protective antibodies. Antigen-activated B cells—with T-cell help—undergo affinity maturation within germinal centres and persist as long-lived IgG plasma cells in the bone marrow. Here we show that antigen-specific, induced IgM plasma cells also persist for a lifetime. Unlike long-lived IgG plasma cells, which develop in germinal centres and then home to the bone marrow, IgM plasma cells are primarily retained within the spleen and can develop even in the absence of germinal centres. Interestingly, their expressed IgV loci exhibit somatic mutations introduced by the activation-induced cytidine deaminase (AID). However, these IgM plasma cells are probably not antigen-selected, as replacement mutations are spread through the variable segment and not enriched within the CDRs. Finally, antibodies from long-lived IgM plasma cells provide protective host immunity against a lethal virus challenge.

Long-lived IgG plasma cells develop in germinal centres and then home to the bone marrow and persist for a lifetime. Here the authors identify long-lived IgM plasma cells in the murine spleen, which carry IgH mutations but can develop independently of germinal centres, and confer protective antiviral immunity.

B-cell hyperfunction in children with immune thrombocytopenic purpura persists after splenectomy

BACKGROUND

Immune thrombocytopenic purpura (ITP) is characterized by reduced platelet count secondary to immune-mediated destruction, this results in an increased bleeding risk. Autoantibodies binding to platelets tag them for premature destruction in the spleen. For this reason, splenectomy is often performed as treatment of chronic forms of disease that are resistant to pharmacological therapy.

METHODS

We studied 30 patients with ITP and compared them with age-matched controls.

RESULTS

We show that B cells of patients with chronic ITP are intrinsically hyperreactive, producing more than normal IgG in vivo and plasma cells in vitro. In normal individuals after splenectomy, a significant depletion of memory B cells is observed, associated with loss of reactivity to CpG oligodeoxynucleotide and consequent inability to form antibody-producing cells. In Enzyme-Linked ImmunoSpot Methods, we compared three splenectomized ITP patients relapsing after surgery, 30 healthy controls, and 37 individuals splenectomized for trauma, spherocytosis, thalassemia, nonhematological tumor, and other diseases.

CONCLUSIONS

We confirmed that B cells of ITP patients remain hyperreactive in vitro and form high numbers of antibody-producing cells after splenectomy. Thus, chronic ITP may be associated with intrinsic B-cell hyperfunction, leading to the production of antibodies with multiple specificities including that against platelets.