Differential responses to Ig and class II-mediated signals in splenic B cell subsets from normal and autoimmune mice.

B cells of mouse and human can be divided into distinct subpopulations, differing in distribution and phenotype. It is not known, however, whether B cell subsets respond similarly to signals mediated by cognate interactions with T cells, such as ligation of the B cell class II MHC molecule. Mouse splenic B cells proliferate in response to a combination of non-mitogenic anti-mu mAb, IL-4 and class II MHC-specific mAbs. In order to assess the response of B cell subpopulations to these signals, B cells were separated on the basis of CD23 expression. Previous studies have shown that CD23 expression is useful in distinguishing marginal zone from follicular B cells and peritoneal B1 from B2 B cells. B cells of both subsets responded to the combination of signals, but CD23- B cells showed a higher response. Splenic B cells were also purified from several strains of autoimmune mice, of interest because their disease features expansion of CD23- B cells and autoantibody production. While normal B cells showed no response to non-mitogenic anti-mu mAb alone, B cells from autoimmune mice showed a marked decrease in proliferation. Addition of IL-4 plus class II-specific mAbs restored increased proliferation. Again, responses were higher in CD23- than in CD23+ B cells. These findings suggest that CD23- B cells are especially responsive to signals delivered through class II and the IL-4 receptor. These signals may allow preferential rescue of CD23-B cells from antigen-mediated tolerance and result in their hyperexpansion in response to autoreactive T cells.