Amplified B Lymphocyte CD40 Signaling Drives Regulatory B10 Cell Expansion in Mice

Aberrant CD40 ligand (CD154) expression occurs on both T cells and B cells in human lupus patients, which is suggested to enhance B cell CD40 signaling and play a role in disease pathogenesis. Transgenic mice expressing CD154 by their B cells (CD154(TG)) have an expanded spleen B cell pool and produce autoantibodies (autoAbs). CD22 deficient (CD22(-/-)) mice also produce autoAbs, and importantly, their B cells are hyper-proliferative following CD40 stimulation ex vivo. Combining these 2 genetic alterations in CD154(TG)CD22(-/-) mice was thereby predicted to intensify CD40 signaling and autoimmune disease due to autoreactive B cell expansion and/or activation.CD154(TG)CD22(-/-) mice were assessed for their humoral immune responses and for changes in their endogenous lymphocyte subsets. Remarkably, CD154(TG)CD22(-/-) mice were not autoimmune, but instead generated minimal IgG responses against both self and foreign antigens. This paucity in IgG isotype switching occurred despite an expanded spleen B cell pool, higher serum IgM levels, and augmented ex vivo B cell proliferation. Impaired IgG responses in CD154(TG)CD22(-/-) mice were explained by a 16-fold expansion of functional, mature IL-10-competent regulatory spleen B cells (B10 cells: 26.7×10(6)±6 in CD154(TG)CD22(-/-) mice; 1.7×10(6)±0.4 in wild type mice, p<0.01), and an 11-fold expansion of B10 cells combined with their ex vivo-matured progenitors (B10+B10pro cells: 66×10(6)±3 in CD154(TG)CD22(-/-) mice; 6.1×10(6)±2 in wild type mice, p<0.01) that represented 39% of all spleen B cells.These results demonstrate for the first time that the IL-10-producing B10 B cell subset has the capacity to suppress IgG humoral immune responses against both foreign and self antigens. Thereby, therapeutic agents that drive regulatory B10 cell expansion in vivo may inhibit pathogenic IgG autoAb production in humans

A distinct role for B1b lymphocytes in T cell-independent immunity

Pathogenesis of infectious disease is not only determined by the virulence of the microbe but also by the immune status of the host. Vaccination is the most effective means to control infectious diseases. A hallmark of the adaptive immune system is the generation of B cell memory, which provides a long-lasting protective antibody response that is central to the concept of vaccination. Recent studies revealed a distinct function for B1b lymphocytes, a minor subset of mature B cells that closely resembles that of memory B cells in a number of aspects. In contrast to the development of conventional B cell memory, which requires the formation of germinal centers and T cells, the development of B1b cell-mediated long-lasting antibody responses occurs independent of T cell help. T cell-independent (TI) antigens are important virulence factors expressed by a number of bacterial pathogens, including those associated with biological threats. TI antigens cannot be processed and presented to T cells and therefore are known to possess restricted T cell-dependent (TD) immunogenicity. Nevertheless, specific recognition of TI antigens by B1b cells and the highly protective antibody responses mounted by them clearly indicate a crucial role for this subset of B cells. Understanding the mechanisms of long-term immunity conferred by B1b cells may lead to improved vaccine efficacy for a variety of TI antigens

Functional activity of CD40 antibodies correlates to the position of binding relative to CD154

In this study we describe the characterization of a panel of 12 anti-mouse CD40 monoclonal antibodies (mAb). Characterization was performed in terms of antibody-binding site relative to the CD154 ligand, and the relationship between position and functional outcome of binding. The antibodies divided into three groups. The first were strong inhibitors of CD154 binding, and induced strong proliferative and activation signals to B cells. Two antibodies gave intermediary inhibition and comparable levels of activation. The remaining antibodies were found to bind outside the CD154 binding site and were poor inducers of B-cell activation. Data presented show a strong correlation between location of mAb binding and the resultant activation signal delivered. This correlation is shown to be independent of the isotype of the antibody involved and of its affinity. Implications of these findings are discussed

Survey of naturally occurring CD4(+) T cell responses against NY-ESO-1 in cancer patients: Correlation with antibody responses

NY-ESO-1 is one of the most immunogenic proteins described in human cancers, based on its capacity to elicit simultaneous antibody and CD8(+) T cell responses in vivo. Although HLA class II restricted epitopes from NY-ESO-1 have been identified, no broad survey has yet established the status of natural CD4(+) T cell responses in cancer patients in relation to CD8(+) and antibody responses. We used a recently developed general strategy for monitoring CD4(+) responses that overcomes the need for prior knowledge of epitope or HLA restriction to analyze a series of 31 cancer patients and healthy donors for the presence of CD4(+) T cells to NY-ESO-1, and related this response to NY-ESO-1 expression in tumor cells and serum antibodies to NY-ESO-1. None of the 18 patients that tested seronegative for NY-ESO-1 had detectable CD4(+) T cell responses. On the contrary, 11 of 13 cancer patients with serum antibodies to NY-ESO-1 had polyclonal CD4(+) T cell responses directed against various known and previously undescribed NY-ESO-1 epitopes. NY-ESO-1 peptide 80–109 was the most immunogenic, with 10 of 11 patients responding to this peptide. We show here that 12-mer determinants from NY-ESO-1 eliciting a CD4(+) T cell response were peptide 87–98 with promiscuous HLA class II presentation, peptide 108–119 restricted by HLA-DP4, and peptides 121–132 and 145–156, both shorter epitopes from previously described HLA-DR4 peptides, also presented by HLA-DR7. This study represents the next step in compiling a comprehensive picture of the adaptive immune response to NY-ESO-1, and provides a general strategy for analyzing the CD4(+) T cell response to other tumor antigens eliciting a humoral immune response