Discrete T cell populations with specificity for a neo-self-antigen bear distinct imprints of tolerance

Mice expressing the Torpedo acetylcholine receptor alpha-chain as a neo-self-Ag exhibit a reduced frequency of T cells responding to the immunodominant epitope Talpha146-162 indicating a degree of tolerance. We characterized tolerance induction in these animals by analyzing the residual Talpha146-162-responsive T cell population and comparing it to that of nontransgenic littermates. Using CD4(high) sorting, we isolated the vast majority of Ag-reactive T cells from both strains of mice. Quantitative studies of the CD4(high) populations in transgenic mice following immunization with Talpha146-162 revealed a diminished expansion of cells expressing the canonical TCRBV6 but not other TCRBV gene segments when compared with nontransgenic littermates. In addition, CD4(high) cells from transgenic mice were functionally hyporesponsive to Talpha146-162 in terms of proliferation and cytokine secretion regardless of TCRBV gene segment use. TCR sequence analysis of transgenic Vbeta6(+)CD4(high) cells revealed a reduced frequency of cells expressing a conserved motif within the TCRbeta CDR3. Thus, the canonical Talpha146-162 responsive, Vbeta6(+) population demonstrates both quantitative and qualitative deficits that correlate with an altered TCR repertoire whereas the non-Vbeta6 population in transgenic mice exhibits only a reduction in peptide responsiveness, a qualitative defect. These data demonstrate that discrete autoreactive T cell populations with identical peptide/MHC specificity in Torpedo acetylcholine receptor-alpha-transgenic animals bear distinct tolerance imprints.