We characterized the cell types involved in the H-2-controlled suppression of T cell response to lactate dehydrogenase B (LDHB). The suppressor effector (Tse) was found to be an Lyt-1+2+, J+ cell that recognizes antigen together with Ek molecules of antigen-presenting cells (APC). To become functional, the Tse cell requires a second signal from a nonspecific, Lyt-1+2-, J+ suppressor-inducer (Tsi) cell. The Tsi-Tse interaction is not subject to any genetic restriction. The target cell of suppression is an Lyt-1+2-, J- (most likely T helper [Th]) cell that recognizes LDHB in the context of A molecules on APC. The suppression is manifested in inhibition of the antigen-specific, A-restricted proliferation of Th cells. The interaction between Tse and Th is restricted by the A region of the H-2 complex. Because this restriction is determined by the receptor of Th cells, the mechanism of Th-Tse interaction most likely involves a concomitant recognition of LDHB and A region-controlled molecules by Th cells on the surface of Tse cells.

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