Suppression of insulitis and diabetes in B cell-deficient mice treated with streptozocin: B cells are essential for the TCR clonotype spreading of islet-infiltrating T cells

In order to clarify the role of B cells in the development of insulitis and diabetes, B cell-deficient (B^-) mice treated with streptozocin (STZ) were studied. The extent of insulitis and the cumulative incidence of diabetes were significantly suppressed in B^- mice (P<0.0001), indicating that B cells are crucial for the progression of insulitis and diabetes. Accumulation of both CD4⁺ T cells and B cells was observed in islets of B⁺ mice, while CD4⁺ T cells but not B cells were found in B^- mice. A few CD8⁺ T cells and macrophages were detectable in both types of mice. The immunohistochemical study did not reveal any change in the subpopulations of infiltrating lymphocytes except for the absence of B cells in the B^- mice. TCR Vβ gene repertoire usage of islet-infiltrating T cells was restricted to some extent in the B⁺ or B^- mice, but there was no significant difference between the B⁺ and B^- mice, suggesting that the initial islet-reactive T cell response can occur in the absence of B cells. In contrast, TCR clonotype spreading of islet-infiltrating T cells was significantly suppressed in B^- mice compared with B⁺ mice (P<0.0001). These data suggest that initial priming of T cells is not impaired and TCR Vβ repertoire usage is not limited by the lack of B cells, while B cells are important essentially for the spreading of islet-infiltrating clonal T cells in autoimmune diabetic mice induced with STZ.