Preexisting and de novo humoral immunity to SARS-CoV-2 in humans

Zoonotic introduction of novel coronaviruses may encounter preexisting immunity in humans. Using diverse assays for antibodies recognizing SARS-CoV-2 proteins, we detected preexisting humoral immunity. SARS-CoV-2 spike glycoprotein (S)-reactive antibodies were detectable using a flow cytometry-based method in SARS-CoV-2-uninfected individuals and were particularly prevalent in children and adolescents. They were predominantly of the immunoglobulin G (IgG) class and targeted the S2 subunit. By contrast, SARS-CoV-2 infection induced higher titers of SARS-CoV-2 S-reactive IgG antibodies targeting both the S1 and S2 subunits, and concomitant IgM and IgA antibodies, lasting throughout the observation period. SARS-CoV-2-uninfected donor sera exhibited specific neutralizing activity against SARS-CoV-2 and SARS-CoV-2 S pseudotypes. Distinguishing preexisting and de novo immunity will be critical for our understanding of susceptibility to and the natural course of SARS-CoV-2 infection.

Regulation of the germinal center reaction by Foxp3+ follicular regulatory T cells

Follicular helper T (T(FH)) cells participate in humoral responses providing selection signals to germinal center B cells. Recently, expression of CXCR5, PD-1, and the transcription factor Bcl-6 has allowed the identification of T(FH) cells. We found that a proportion of follicular T cells, with phenotypic characteristics of T(FH) cells and expressing Foxp3, are recruited during the course of a germinal center (GC) reaction. These Foxp3(+) cells derive from natural regulatory T cells. To establish the in vivo physiologic importance of Foxp3(+) follicular T cells, we used CXCR5-deficient Foxp3(+) cells, which do not have access to the follicular region. Adoptive cell transfers of CXCR5-deficient Foxp3(+) cells have shown that Foxp3(+) follicular T cells are important regulators of the GC reaction following immunization with a thymus-dependent Ag. Our in vivo data show that Foxp3(+) follicular T cells can limit the magnitude of the GC reaction and also the amount of secreted Ag-specific IgM, IgG1, IgG2b, and IgA. Therefore, Foxp3(+) follicular regulatory T cells appear to combine characteristics of T(FH) and regulatory T cells for the control of humoral immune responses.

Human blood Tfr cells are indicators of ongoing humoral activity not fully licensed with suppressive function

Germinal center (GC) responses are controlled by T follicular helper (Tfh) and T follicular regulatory (Tfr) cells and are crucial for the generation of high-affinity antibodies. Although the biology of human circulating and tissue Tfh cells has been established, the relationship between blood and tissue Tfr cells defined as CXCR5+Foxp3+ T cells remains elusive. We found that blood Tfr cells are increased in Sjögren syndrome, an autoimmune disease with ongoing GC reactions, especially in patients with high autoantibody titers, as well as in healthy individuals upon influenza vaccination. Although blood Tfr cells correlated with humoral responses, they lack full B cell-suppressive capacity, despite being able to suppress T cell proliferation. Blood Tfr cells have a naïve-like phenotype, although they are absent from human thymus or cord blood. We found that these cells were generated in peripheral lymphoid tissues before T-B interaction, as they are maintained in B cell-deficient patients. Therefore, blood CXCR5+Foxp3+ T cells in human pathology indicate ongoing humoral activity but are not fully competent circulating Tfr cells.

Identification of regulatory Foxp3+ invariant NKT cells induced by TGF-beta

Invariant NKT (iNKT) cells were shown to prevent the onset of experimental autoimmune encephalomyelitis in mice following administration of their specific TCR agonist alpha-galactosylceramide. We found that this protection was associated with the emergence of a Foxp3(+) iNKT cell population in cervical lymph nodes. We demonstrate that the differentiation of these cells is critically dependent on TGF-beta in both mice and humans. Moreover, in vivo generation of Foxp3(+) iNKT cells was observed in the TGF-beta-rich environment of the murine gut. Foxp3(+) iNKT cells displayed a phenotype similar to that of Foxp3(+) regulatory T cells, and they suppress through a contact-dependent, glucocorticoid-induced TNFR-mediated mechanism. Nevertheless, Foxp3(+) iNKT cells retain distinctive NKT cell characteristics, such as promyelocytic leukemia zinc finger protein expression and preferential homing to the liver following adoptive transfer, where they stably maintained Foxp3 expression. Our data thus unveil an unexpected capacity of iNKT cells to acquire regulatory functions that may contribute to the establishment of immunological tolerance.

Adaptive immunity and neutralizing antibodies against SARS-CoV-2 variants of concern following vaccination in patients with cancer: The CAPTURE study

CAPTURE (NCT03226886) is a prospective cohort study of COVID-19 immunity in patients with cancer. Here we evaluated 585 patients following administration of two doses of BNT162b2 or AZD1222 vaccines, administered 12 weeks apart. Seroconversion rates after two doses were 85% and 59% in patients with solid and hematological malignancies, respectively. A lower proportion of patients had detectable neutralizing antibody titers (NAbT) against SARS-CoV-2 variants of concern (VOCs) vs wildtype (WT). Patients with hematological malignancies were more likely to have undetectable NAbT and had lower median NAbT vs solid cancers against both WT and VOCs. In comparison with individuals without cancer, patients with haematological, but not solid, malignancies had reduced NAb responses. Seroconversion showed poor concordance with NAbT against VOCs. Prior SARS-CoV-2 infection boosted NAb response including against VOCs, and anti-CD20 treatment was associated with undetectable NAbT. Vaccine-induced T-cell responses were detected in 80% of patients, and were comparable between vaccines or cancer types. Our results have implications for the management of cancer patients during the ongoing COVID-19 pandemic.

The Ratio of Blood T Follicular Regulatory Cells to T Follicular Helper Cells Marks Ectopic Lymphoid Structure Formation While Activated Follicular Helper T Cells Indicate Disease Activity in Primary Sjögren's Syndrome

OBJECTIVE

To investigate whether the balance of blood follicular helper T (Tfh) cells and T follicular regulatory (Tfr) cells can provide information about ectopic lymphoid neogenesis and disease activity in primary Sjögren's syndrome (SS).

METHODS

We prospectively recruited 56 patients clinically suspected of having SS. Sixteen of these patients subsequently fulfilled the American-European Consensus Group criteria for SS and were compared to 16 patients with non-SS sicca syndrome. Paired blood and minor salivary gland (MSG) biopsy samples were analyzed to study Tfr cells and subsets of Tfh cells in both compartments.

RESULTS

Patients with primary SS had normal Tfh cell counts in peripheral blood; however, activated programmed death 1-positive (PD-1+) inducible costimulator-positive (ICOS+) Tfh cells in peripheral blood were strongly associated with disease activity assessed by the European League Against Rheumatism Sjögren's Syndrome Disease Activity Index (r = 0.8547, P = 0.0008). Conversely, the blood Tfr cell:Tfh cell ratio indicated ectopic lymphoid structure formation in MSGs, being strongly associated with B cell, CD4+ T cell, and PD-1+ICOS+ T cell infiltration in MSGs, and was especially increased in patients with focal sialadenitis. Further analysis showed that the blood Tfr cell:Tfh cell ratio allowed discrimination between SS patients and healthy donors with excellent accuracy and was a strong predictor of SS diagnosis (odds ratio [OR] 12.96, P = 0.028) and the presence of focal sialadenitis (OR 10, P = 0.022) in patients investigated for sicca symptoms, thus highlighting the potential clinical value of this marker.

CONCLUSION

The blood Tfr cell:Tfh cell ratio and PD-1+ICOS+ Tfh cells constitute potential novel biomarkers for different features of primary SS. While the blood Tfr cell:Tfh cell ratio is associated with ectopic lymphoid neogenesis, activated Tfh cells indicate disease activity.

Induced IL-17-producing invariant NKT cells require activation in presence of TGF-β and IL-1β

IL-17 production by innate-like lymphocytes, including γδ and invariant NKT (iNKT) cells, have been ascribed to specific lineages that are endowed with this functional specialization during thymic differentiation. IL-17-producing iNKT cells have been described as a CD4(-)NK1.1(-) lineage in mice and CD161(+) in humans. We found that, in mice, noncommitted iNKT cells can be induced to produce IL-17 when activated in presence of TGF-β and IL-1β. This peripheral induction of IL-17 expression could be observed in any subset irrespectively of CD4 and NK1.1 expression, the process leading to loss of NK1.1 expression and partial CD4 downmodulation. Furthermore, induced IL-17-producing iNKT cells were sufficient to drive neutrophilic airways inflammation upon intratracheal adoptive cell transfer into congenic mice. Taken together, our data show that similarly to regulatory T cells, which have a natural and peripherally induced subset, IL-17 production by iNKT cells can also be imprinted in natural iNKT17 cells or peripherally induced.

T follicular regulatory cells in mice and men

It has long been known that CD4 T cells are necessary to provide help to B cells, triggering a germinal centre (GC) reaction where affinity maturation and isotype switching occur. However, the nature of the dedicated CD4 helper T cells, known as T follicular helper (Tfh), was only recently described. Here, we review the biology and function of the recently described T follicular regulatory (Tfr) cells, another CD4 T-cell population also found within GCs but with regulatory function and characteristics. Tfr cells have been identified in mice and humans as simultaneously presenting characteristics of T follicular cells (namely CXCR5 expression) and regulatory T cells (including Foxp3 expression). These Tfr cells have been implicated in the regulation of the magnitude of the GC reaction, as well as in protection from immune-mediated pathology.

Functional antibody and T cell immunity following SARS-CoV-2 infection, including by variants of concern, in patients with cancer: the CAPTURE study

Patients with cancer have higher COVID-19 morbidity and mortality. Here we present the prospective CAPTURE study, integrating longitudinal immune profiling with clinical annotation. Of 357 patients with cancer, 118 were SARS-CoV-2 positive, 94 were symptomatic and 2 died of COVID-19. In this cohort, 83% patients had S1-reactive antibodies and 82% had neutralizing antibodies against wild type SARS-CoV-2, whereas neutralizing antibody titers against the Alpha, Beta and Delta variants were substantially reduced. S1-reactive antibody levels decreased in 13% of patients, whereas neutralizing antibody titers remained stable for up to 329 days. Patients also had detectable SARS-CoV-2-specific T cells and CD4+ responses correlating with S1-reactive antibody levels, although patients with hematological malignancies had impaired immune responses that were disease and treatment specific, but presented compensatory cellular responses, further supported by clinical recovery in all but one patient. Overall, these findings advance the understanding of the nature and duration of the immune response to SARS-CoV-2 in patients with cancer.

The role of human umbilical cord tissue-derived mesenchymal stromal cells (UCX®) in the treatment of inflammatory arthritis

BACKGROUND

ECBio has developed proprietary technology to consistently isolate, expand and cryopreserve a well-characterized population of stromal cells from human umbilical cord tissue (UCX® cells). The technology has recently been optimized in order to become compliant with Advanced Medicine Therapeutic Products. In this work we report the immunosuppressive capacity of UCX® cells for treating induced autoimmune inflammatory arthritis.

METHODS

UCX® cells were isolated using a proprietary method (PCT/IB2008/054067) that yields a well-defined number of cells using a precise proportion between tissue digestion enzyme activity units, tissue mass, digestion solution volume and void volume. The procedure includes three recovery steps to avoid non-conformities related to cell recovery. UCX® surface markers were characterized by flow cytometry and UCX® capacity to expand in vitro and to differentiate into adipocyte, chondrocyte and osteoblast-like cells was evaluated. Mixed Lymphocyte Reaction (MLR) assays were performed to evaluate the effect of UCX® cells on T-cell activation and Treg conversion assays were also performed in vitro. Furthermore, UCX® cells were administered in vivo in both a rat acute carrageenan-induced arthritis model and rat chronic adjuvant induced arthritis model for arthritic inflammation. UCX® anti-inflammatory activity was then monitored over time.

RESULTS

UCX® cells stained positive for CD44, CD73, CD90 and CD105; and negative for CD14, CD19 CD31, CD34, CD45 and HLA-DR; and were capable to differentiate into adipocyte, chondrocyte and osteoblast-like cells. UCX® cells were shown to repress T-cell activation and promote the expansion of Tregs better than bone marrow mesenchymal stem cells (BM-MSCs). Accordingly, xenogeneic UCX® administration in an acute carrageenan-induced arthritis model showed that human UCX® cells can reduce paw edema in vivo more efficiently than BM-MSCs. Finally, in a chronic adjuvant induced arthritis model, animals treated with intra-articular (i.a.) and intra-peritoneal (i.p.) infusions of UCX® cells showed faster remission of local and systemic arthritic manifestations.

CONCLUSION

The results suggest that UCX® cells may be an effective and promising new approach for treating both local and systemic manifestations of inflammatory arthritis.

Modulation of IL-17 and Foxp3 expression in the prevention of autoimmune arthritis in mice

BACKGROUND

Rheumatoid Arthritis (RA) is a chronic immune mediated disease associated with deregulation of many cell types. It has been reported that different T cell subsets have opposite effects in disease pathogenesis, in particular Th17 and Treg cells.

METHODOLOGY AND FINDINGS

We investigated whether non-depleting anti-CD4 monoclonal antibodies, which have been reported as pro-tolerogenic, can lead to protection from chronic autoimmune arthritis in SKG mice--a recently described animal model of RA--by influencing the Th17/Treg balance. We found that non-depleting anti-CD4 prevented the onset of chronic autoimmune arthritis in SKG mice. Moreover, treated mice were protected from the induction of arthritis up to 60 days following anti-CD4 treatment, while remaining able to mount CD4-dependent immune responses to unrelated antigens. The antibody treatment also prevented disease progression in arthritic mice, although without leading to remission. Protection from arthritis was associated with an increased ratio of Foxp3, and decreased IL-17 producing T cells in the synovia. In vitro assays under Th17-polarizing conditions showed CD4-blockade prevents Th17 polarization, while favoring Foxp3 induction.

CONCLUSIONS

Non-depleting anti-CD4 can therefore induce long-term protection from chronic autoimmune arthritis in SKG mice through reciprocal changes in the frequency of Treg and Th17 cells in peripheral tissues, thus shifting the balance towards immune tolerance.

Defining the identity and the niches of epithelial stem cells with highly pleiotropic multilineage potency in the human thymus

Thymus is necessary for lifelong immunological tolerance and immunity. It displays a distinctive epithelial complexity and undergoes age-dependent atrophy. Nonetheless, it also retains regenerative capacity, which, if harnessed appropriately, might permit rejuvenation of adaptive immunity. By characterizing cortical and medullary compartments in the human thymus at single-cell resolution, in this study we have defined specific epithelial populations, including those that share properties with bona fide stem cells (SCs) of lifelong regenerating epidermis. Thymic epithelial SCs display a distinctive transcriptional profile and phenotypic traits, including pleiotropic multilineage potency, to give rise to several cell types that were not previously considered to have shared origin. Using here identified SC markers, we have defined their cortical and medullary niches and shown that, in vitro, the cells display long-term clonal expansion and self-organizing capacity. These data substantively broaden our knowledge of SC biology and set a stage for tackling thymic atrophy and related disorders.

IL-9 Expression by Invariant NKT Cells Is Not Imprinted during Thymic Development

Invariant NKT (iNKT) cell thymic development can lead to distinct committed effector lineages, namely NKT1, NKT2, and NKT17. However, following identification of IL-9-producing iNKT cells involved in mucosal inflammation, their development remains unaddressed. In this study, we report that although thymic iNKT cells from naive mice do not express IL-9, iNKT cell activation in the presence of TGF-β and IL-4 induces IL-9 secretion in murine and human iNKT cells. Acquisition of IL-9 production was observed in different iNKT subsets defined by CD4, NK1.1, and neuropilin-1, indicating that distinct functional subpopulations are receptive to IL-9 polarization. Transcription factor expression kinetics suggest that regulatory mechanisms of IL-9 expression are shared by iNKT and CD4 T cells, with Irf4 and Batf deficiency deeply affecting IL-9 production. Importantly, adoptive transfer of an enriched IL-9(+) iNKT cell population leads to exacerbated allergic inflammation in the airways upon intranasal immunization with house dust mite, confirming the ability of IL-9-producing iNKT cells to mediate proinflammatory effects in vivo, as previously reported. Taken together, our data show that peripheral iNKT cells retain the capacity of shaping their function in response to environmental cues, namely TGF-β and IL-4, adopting an IL-9-producing NKT cell phenotype able to mediate proinflammatory effects in vivo, namely granulocyte and mast cell recruitment to the lungs.

Regulatory T cell maintenance of dominant tolerance: induction of tissue self-defense?

In the last decade there has been an increasing interest for the action of regulatory T cells (Treg) in preventing transplant rejection, autoimmunity and other inflammatory diseases and in maintaining dominant tolerance. It is becoming clear that such regulatory function does not rely simply on direct inhibition of "aggressive" T cells. In fact, several studies suggest that Treg cells may induce changes in the target tissue, promoting a state of "immune privilege" where protective genes such as heme oxygenase-1 (HO-1) and indolamine 2,3 dioxygenase (IDO) may have a critical role.

T cell apoptosis and induction of Foxp3+ regulatory T cells underlie the therapeutic efficacy of CD4 blockade in experimental autoimmune encephalomyelitis

The pathogenesis of multiple sclerosis requires the participation of effector neuroantigen-specific T cells. Thus, T cell targeting has been proposed as a promising therapeutic strategy. However, the mechanism underlying effective disease prevention following T cell targeting remains incompletely known. We found, using several TCR-transgenic strains, that CD4 blockade is effective in preventing experimental autoimmune encephalopathy and in treating mice after the disease onset. The mechanism does not rely on direct T cell depletion, but the anti-CD4 mAb prevents the proliferation of naive neuroantigen-specific T cells, as well as acquisition of effector Th1 and Th17 phenotypes. Simultaneously, the mAb favors peripheral conversion of Foxp3(+) regulatory T cells. Pre-existing effector cells, or neuroantigen-specific cells that undergo cell division despite the presence of anti-CD4, are committed to apoptosis. Therefore, protection from experimental autoimmune encephalopathy relies on a combination of dominant mechanisms grounded on regulatory T cell induction and recessive mechanisms based on apoptosis of neuropathogenic cells. We anticipate that the same mechanisms may be implicated in other T cell-mediated autoimmune diseases that can be treated or prevented with Abs targeting T cell molecules, such as CD4 or CD3.

Prevention of house dust mite induced allergic airways disease in mice through immune tolerance

Allergic airways disease is a consequence of a Th2 response to an allergen leading to a series of manifestations such as production of allergen-specific IgE, inflammatory infiltrates in the airways, and airway hyper-reactivity (AHR). Several strategies have been reported for tolerance induction to allergens leading to protection from allergic airways disease. We now show that CD4 blockade at the time of house dust mite sensitization induces antigen-specific tolerance in mice. Tolerance induction is robust enough to be effective in pre-sensitized animals, even in those where AHR was pre-established. Tolerant mice are protected from airways eosinophilia, Th2 lung infiltration, and AHR. Furthermore, anti-CD4 treated mice remain immune competent to mount immune responses, including Th2, to unrelated antigens. Our findings, therefore, describe a strategy for tolerance induction potentially applicable to other immunogenic proteins besides allergens.

Route of Antigen Presentation Can Determine the Selection of Foxp3-Dependent or Foxp3-Independent Dominant Immune Tolerance

It has been shown that dominant tolerance, namely in transplantation, requires Foxp3⁺ regulatory T cells. Although most tolerance-inducing regimens rely on regulatory T cells, we found that induction of tolerance to proteins in aluminum hydroxide can be achieved in Foxp3-deficient mice using nondepleting anti-CD4 Abs. This type of tolerance is Ag specific, and tolerant mice retain immune competence to respond to unrelated Ags. We demonstrated with chicken OVA-specific TCR-transgenic mice that the same tolerizing protocol (CD4 blockade) and the same target Ag (OVA) achieves Foxp3-dependent transplantation tolerance to OVA-expressing skin grafts, but Foxp3-independent tolerance when the Ag is provided as OVA-aluminum hydroxide. In the latter case, we found that tolerance induction triggered recessive mechanisms leading to elimination of effector cells and, simultaneously, a dominant mechanism associated with the emergence of an anergic and regulatory CTLA-4⁺IL-2^lowFoxp3^- T cell population, where the tolerance state is IL-10 dependent. Such Foxp3-independent mechanisms can improve the efficacy of tolerance-inducing protocols.

Preexisting and de novo humoral immunity to SARS-CoV-2 in humans

Zoonotic introduction of novel coronaviruses may encounter preexisting immunity in humans. Using diverse assays for antibodies recognizing SARS-CoV-2 proteins, we detected preexisting humoral immunity. SARS-CoV-2 spike glycoprotein (S)-reactive antibodies were detectable using a flow cytometry-based method in SARS-CoV-2-uninfected individuals and were particularly prevalent in children and adolescents. They were predominantly of the immunoglobulin G (IgG) class and targeted the S2 subunit. By contrast, SARS-CoV-2 infection induced higher titers of SARS-CoV-2 S-reactive IgG antibodies targeting both the S1 and S2 subunits, and concomitant IgM and IgA antibodies, lasting throughout the observation period. SARS-CoV-2-uninfected donor sera exhibited specific neutralizing activity against SARS-CoV-2 and SARS-CoV-2 S pseudotypes. Distinguishing preexisting and de novo immunity will be critical for our understanding of susceptibility to and the natural course of SARS-CoV-2 infection.

The fate of CD4+ T cells under tolerance-inducing stimulation: a modeling perspective

Non-depleting anti-CD4 monoclonal antibodies (MAbs) induce long-term dominant tolerance mediated by regulatory T cells in several animal models of transplantation, allergy and autoimmunity. However, despite many studies on tolerance induction following CD4 blockade, the consequences of this intervention on T-cell kinetics are still unknown. Mathematical models have been useful to understand lymphocyte dynamics, estimating rates of proliferation and cell death following an intervention. Using the same strategy, we found that CD4(+) T cells activated in vitro in the presence of non-depleting anti-CD4 MAbs are prevented from undergoing optimal proliferation and show a higher frequency of apoptosis. Although the changes are small, during the course of a proliferative response, they lead to very distinct final levels of cell numbers. The importance of these mechanisms, predicted by the mathematical model, was validated by showing that lck-driven Bcl-x(L) transgenic mice, bearing T cells resistant to apoptosis, fail to become tolerant to skin grafts following CD4-blockade. Our data show that, in addition to induction of regulatory T cells, CD4 blockade has a marked effect in the effector T-cell pool by the combined action of hindering proliferation while favoring apoptosis. It is, therefore, the combination of all those mechanisms that leads to stable tolerance.

Induction of dominant tolerance using monoclonal antibodies

Monoclonal antibodies (MAb) have been shown to be effective in inducing immune tolerance in transplantation and autoimmunity. Several different MAb have tolerogenic properties and their effect has been studied in a range of experimental animal models and, in some cases, in clinical trials. The tolerant state seems to be maintained by CD4+ regulatory T cells (Treg), induced in the periphery, capable of suppressing other T cells specific for the same antigens or antigens presented by the same antigen presenting cells. Furthermore, following the initial induction of Treg cells under MAb treatment, Treg cells themselves can maintain the tolerant state in a dominant way in the absence of the therapeutic MAb or other immunosuppressive agents, and are able to recruit other T cells into the regulatory pool--a process named infectious tolerance.

Functional antibody and T-cell immunity following SARS-CoV-2 infection, including by variants of concern, in patients with cancer: the CAPTURE study

Patients with cancer have higher COVID-19 morbidity and mortality. Here we present the prospective CAPTURE study (NCT03226886) integrating longitudinal immune profiling with clinical annotation. Of 357 patients with cancer, 118 were SARS-CoV-2-positive, 94 were symptomatic and 2 patients died of COVID-19. In this cohort, 83% patients had S1-reactive antibodies, 82% had neutralizing antibodies against WT, whereas neutralizing antibody titers (NAbT) against the Alpha, Beta, and Delta variants were substantially reduced. Whereas S1-reactive antibody levels decreased in 13% of patients, NAbT remained stable up to 329 days. Patients also had detectable SARS-CoV-2-specific T cells and CD4+ responses correlating with S1-reactive antibody levels, although patients with hematological malignancies had impaired immune responses that were disease and treatment-specific, but presented compensatory cellular responses, further supported by clinical. Overall, these findings advance the understanding of the nature and duration of immune response to SARS-CoV-2 in patients with cancer.

B cells from the bench to the clinical practice

B cells develop in bone marrow and undergo antigen-induced activation and terminal differentiation in germinal centres of secondary lymphoid organs. Each B cell is a clone which means that an individual B cell has a unique genetic code and produces only one type of antibody when stimulated by antigen being able to multiply itself and originate several B cells with the same antigen specificity (clonal selection theory). However their important role in adaptive immune responses is supported by the remarkable capacity of recognizing an unlimited array of antigens due to mechanisms of antibody diversity such as V(D)J recombination class switching and somatic hypermutation. B cells can also function as antigen presenting cells that can activate T cells improving the effectiveness of the immune response. Immune B cell tolerance surveillance through clonal deletion anergy and receptor editing is also necessary to avoid pathological conditions like autoimmune diseases. B cells can contribute to autoimmunity by autoantibody production cytokine synthesis antigen presentation T cell activation and ectopic lymphogenesis.