We characterized B cell infiltration of the spinal cord in a B cell-dependent spontaneous model of central nervous system (CNS) autoimmunity that develops in a proportion of mice with mutant T and B cell receptors specific for myelin oligodendrocyte glycoprotein. We found that, while males are more likely to develop disease, females are more likely to have a chronic rather than monophasic disease course. B cell infiltration of the spinal cord was investigated by histology and FACs. CD4+ T cell infiltration was pervasive throughout the white and in some cases gray matter. B cells were almost exclusively restricted to the meninges, often in clusters reminiscent of those described in human multiple sclerosis. These clusters were typically found adjacent to white matter lesions and their presence was associated with a chronic disease course. Extensive investigation of these clusters by histology did not identify features of lymphoid follicles, including organization of T and B cells into separate zones, CD35+ follicular dendritic cells, or germinal centers. The majority of cluster B cells were IgD+ with little evidence of class switch. Consistent with this, B cells isolated from the spinal cord were of the naïve/memory CD38hi CD95lo phenotype. Nevertheless, they were CD62Llo and CD80hi compared to lymph node B cells suggesting that they were at least partly activated and primed to present antigen. Therefore, if meningeal B cells contribute to CNS pathology in autoimmunity, follicular differentiation is not necessary for the pathogenic mechanism.
Generation of specific antibodies during an immune response to infection or vaccination depends on the ability to rapidly and accurately select clones of antibody-secreting B lymphocytes for expansion. Antigen-specific B cell clones undergo the cell fate decision to differentiate into antibody-secreting plasma cells, memory B cells, or germinal center B cells. The E26-transformation-specific (ETS) transcription factors Spi-B and Spi-C are important regulators of B cell development and function. Spi-B is expressed throughout B cell development and is downregulated upon plasma cell differentiation. Spi-C is highly related to Spi-B and has similar DNA-binding specificity. Heterozygosity for Spic rescues B cell development and B cell proliferation defects observed in Spi-B knockout mice. In this study, we show that heterozygosity for Spic rescued defective IgG1 secondary antibody responses in Spib −/− mice. Plasma cell differentiation was accelerated in Spib −/− B cells. Gene expression, ChIP-seq, and reporter gene analysis showed that Spi-B and Spi-C differentially regulated Bach2, encoding a key regulator of plasma cell and memory B cell differentiation. These results suggest that Spi-B and Spi-C oppose the function of one another to regulate B cell differentiation and function.
Once activated, T cells gain the ability to access both healthy and inflamed nonlymphoid tissues. They are then reactivated to remain in the tissue and exert their effector function only if they encounter their specific Ag. In this study, we set out to determine if the same is true for B cells using a mouse model of CNS autoimmunity that incorporates both T and B cell recognition of a myelin autoantigen. Both T and B cells were common infiltrates of spinal cords in diseased mice. However, unlike T cells, anti-myelin B cells were excluded from the inflamed tissue. Further, CNS B cells did not have a phenotype consistent with Ag-specific activation as it occurs in lymphatic tissue. Instead, they expressed elevated levels of CD80, indicating that B cells may contribute to local inflammation through nonantigen-specific mechanisms.
Highlights d B cell fate choices differ in response to model foreign and self-antigen d TCR affinity for antigen influences memory B cell differentiation d The GC response to MOG antigen is short lived d Formation of B cell memory to MOG antigen is defective
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