Central tolerance spares the private high-avidity CD4+ T-cell repertoire specific for an islet antigen in NOD mice

Although central tolerance induces the deletion of most autoreactive T cells, some autoreactive T cells escape thymic censorship. Whether potentially harmful autoreactive T cells present distinct TCR alpha beta features remains unclear. Here, we analyzed the TCR alpha beta repertoire of CD4(+) T cells specific for the S100 beta protein, an islet antigen associated with type 1 diabetes. We found that diabetes-resistant NOD mice deficient for thymus specific serine protease (TSSP), a protease that impairs class II antigen presentation by thymic stromal cells, were hyporesponsive to the immunodominant S100 beta(1-15) epitope, as compared to wild-type NOD mice, due to intrathymic negative selection. In both TSSP-deficient and wild-type NOD mice, the TCR alpha beta repertoire of S100 beta-specific CD4(+) T cells though diverse showed a specific bias for dominant TCR alpha rearrangements with limited CDR3 alpha diversity. These dominant TCR alpha chains were public since they were found in all mice. They were of intermediate-to low-avidity. In contrast, high-avidity T cells expressed unique TCRs specific to each individual (private TCRs) and were only found in wild-type NOD mice. Hence, in NOD mice, the autoreactive CD4(+) T-cell compartment has two major components, a dominant and public low-avidity TCR alpha repertoire and a private high-avidity CD4(+) T-cell repertoire; the latter is deleted by re-enforced negative selection.