B Cells Directly Tolerize CD8⁺ T Cells

This report investigates the response of CD8⁺ T cells to antigens presented by B cells. When C57BL/6 mice were injected with syngeneic B cells coated with the K^b-restricted ovalbumin (OVA) determinant OVA_257–264, OVA-specific cytotoxic T lymphocyte (CTL) tolerance was observed. To investigate the mechanism of tolerance induction, in vitro–activated CD8⁺ T cells from the K^b-restricted, OVA-specific T cell receptor transgenic line OT-I (OT-I cells) were cultured for 15 h with antigen-bearing B cells, and their survival was determined. Antigen recognition led to the killing of the B cells and, surprisingly, to the death of a large proportion of the OT-I CTLs. T cell death involved Fas (CD95), since OT-I cells deficient in CD95 molecules showed preferential survival after recognition of antigen on B cells. To investigate the tolerance mechanism in vivo, naive OT-I T cells were adoptively transferred into normal mice, and these mice were coinjected with antigen-bearing B cells. In this case, OT-I cells proliferated transiently and were then lost from the secondary lymphoid compartment. These data provide the first demonstration that B cells can directly tolerize CD8⁺ T cells, and suggest that this occurs via CD95-mediated, activation-induced deletion.