TOLERANCE IS OVERCOME IN BEEF INSULIN-TRANSGENIC MICE BY ACTIVATION OF LOW-AFFINITY AUTOREACTIVE T-CELLS

To gain insight into the factors controlling the maintenance or loss o f T cell self tolerance we produced beef insulin (BI)-transgenic BALB/ c mice. Transgenic mice express BI under control of the human insulin promoter and secrete physiological amounts of beef insulin. Although t hese mice are tolerant to BI, as evidenced by the lack of insulin-spec ific IgG antibody production following intraperitoneal immunization, t olerance is not complete. Footpad immunization results in a weak antig en-specific T cell proliferative response. indicating the presence of self- reactive BI-specific T cells in the periphery. These T cells are functional in vivo, providing support for IgG1, IgG2a, and IgG2b BI-s pecific antibody production, but require higher concentrations of anti gen than non transgenic T cells (both in vivo and following recall res ponses in vitro) to become activated. In vitro, BI-specific T cell pro liferation in BI-transgenic mice can be largely restored by addition o f interleukin-2, indicating that a significant component of T cell tol erance is mediated by anergy. To characterize the autoreactive T cells that become activated when Tolerance is broken. BI-specific T cell hy bridomas were generated from transgenic mice and compared to a panel o f hybridomas previously derived from nontransgenic BALB/c mice. The ma jority of BI-transgenic hybridomas recognized the immunodominant A1-14 beef insulin peptide but with lower avidity than BALB/c hybridomas. C onsistent with this, none of the dominant T cell receptor rearrangemen ts found in the BALB/c BI-specific T cell receptor repertoire were fou nd in the transgenic hybridomas. These results indicate that, despite evidence for clonal inactivation of many BI-specific T cells in BI-tra nsgenic mice, loss of tolerance results from activation of low-affinit y antigen-specific T cells that appear to have escaped this process.