SUPERANTIGEN-DRIVEN PERIPHERAL DELETION OF T-CELLS - APOPTOSIS OCCURSIN CELLS THAT HAVE LOST THE ALPHA BETA T-CELL RECEPTOR/

Injection of lymphoid cells expressing minor lymphocyte-stimulating an tigen-1 (Mls-1a) induces tolerance to the superantigen, and partial de letion of Mls-1a-reactive T cells. We have identified a transient popu lation 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 proce ss of tolerance induction. Apoptosis was directly demonstrated in this TCR-alpha/beta negative T-cell population. This indicates a periphera l T-cell deletion pathway, characterized by TCR down-regulation, apopt osis, and clonal deletion. The consequence of Mls-1a-induced TCR down- regulation appears to be different in CD4+ cells and in CD8+ cells. Al though most of the CD4+ cells that have lost TCR expressing alpha- and beta-chains appear to be undergoing apoptosis, many of their CD8+ cou nterparts may be able to re-express the Ag receptor. This argues for t he involvement of coreceptors in the induction of apoptosis during per ipheral deletion.