Antibody diversity creates an immunoregulatory challenge for T cells that must cooperate with B cells, yet discriminate between self and nonself. To examine the consequences of T cell reactions to the B cell receptor (BCR), we generated a transgenic (Tg) line of mice expressing a T cell receptor (TCR) specific for a κ variable region peptide in monoclonal antibody (mAb) 36-71. The κ epitope was originally generated by a pair of somatic mutations that arose naturally during an immune response. By crossing this TCR Tg mouse with mice expressing the κ chain of mAb 36-71, we found that κ-specific T cells were centrally deleted in thymi of progeny that inherited the κTg. Maternally derived κTg antibody also induced central deletion. In marked contrast, adoptive transfer of TCR Tg T cells into κTg recipients resulted in T and B cell activation, lymphadenopathy, splenomegaly, and the production of IgG antichromatin antibodies by day 14. In most recipients, autoantibody levels increased with time, Tg T cells persisted for months, and a state of lupus nephritis developed. Despite this, Tg T cells appeared to be tolerant as assessed by severely diminished proliferative responses to the Vκ peptide. These results reveal the importance of attaining central and peripheral T cell tolerance to BCR V regions. They suggest that nondeletional forms of T tolerance in BCR-reactive T cells may be insufficient to preclude helper activity for chromatin-reactive B cells.