Superantigen-driven peripheral deletion of T cells. Apoptosis occurs in cells that have lost the alpha/beta T cell receptor.

Injection of lymphoid cells expressing minor lymphocyte-stimulating antigen-1 (Mls-1a) induces tolerance to the superantigen, and partial deletion of Mls-1a-reactive T cells. We have identified a transient population of T cells that have lost the alpha/beta T cell receptor at the time when Mls-1a-reactive T cells start to disappear during the process of tolerance induction. Apoptosis was directly demonstrated in this TCR-alpha/beta negative T-cell population. This indicates a peripheral T-cell deletion pathway, characterized by TCR down-regulation, apoptosis, and clonal deletion. The consequence of Mls-1a-induced TCR down-regulation appears to be different in CD4+ cells and in CD8+ cells. Although most of the CD4+ cells that have lost TCR expressing alpha- and beta-chains appear to be undergoing apoptosis, many of their CD8+ counterparts may be able to re-express the Ag receptor. This argues for the involvement of coreceptors in the induction of apoptosis during peripheral deletion.