Functional Allelic Exclusion in T Cells

Over the past decade there have been numerous descriptions of suppressor T cells (Ts) and of factors derived from such cells. Several apparently related, but nonidentical, suppressor regulatory pathways consisting of a variety of T-T interactions have been described (1-4). Our laboratory has concentrated on one of these models of antigen-specific suppression involving the hapten 4-hydroxy3-nitrophenyl acetyl (NP). In the NP model system, we have identified at least three distinct suppressor T cell subsets (Tsl, Ts2, Tss) (5-7). Furthermore, we have demonstrated a requirement for accessory cells at various points in the suppressor pathway (8, 9). All of these cellular elements are needed to modulate the contact sensitivity (CS) response to NP. Furthermore, the same T cell populations are required for suppression of NP-specific plaque-forming cell (PFC) responses (10, 1 1). The final effector T cell population in the suppressor cell cascade appears to be an Lyt-2 + subset that we have termed Ts~ (6). Ts3 cells are induced as a consequence of conventional immunization concomitant with the induction of T cells mediating helper or CS activity (8, 12). However, these primed Ts~ cells appear to remain inactive until appropriately triggered by Ts2 cells or a factor derived from Ts9 cells (12, 13). The Ts3 cells are antigen-specific and bind to NP-coated petri dishes (6, 7, 14). They react with anti-Thy-1, anti-Lyt-2, anti-IJ, and anti-NP b (antiidiotype) antisera (6, 7, 14). The activity of Ts3 cells can be demonstrated in cyclophosphamide-treated recipients and is restricted by I-J and Igh genes (6, 12). Ts~ hybridomas that constitutively secrete a suppressor factor, TsFs, have been obtained in the NP system. Five hybridoma T cell lines were prepared by fusion of C57BL/6 (B6) or CKB derived Ts~ cells with the BW5147 thymoma (7). The supernatants from these Ts3 cell hybridomas contain factors (TsF~) which, like Ts~ cells have the capacity to specifically suppress NP-induced CS responses (7).