Abstract
Mixed responder populations, consisting of selected Lyt‐2,3^+^ cells and unselected T cells from two congenic mouse strains differing in their Lyt‐2,3 alleles, were used to study the role of Lyt‐1,2,3^+^ cells in the generation of cytotoxic effector cells in vitro. The fact that, under these conditions, all primary alloreactive and H‐2‐restricted killer cells are generated from the unselected T cell population and not from the selected Lyt‐2,3^+^ subset is demonstrated. Isolated, unsensitized Lyt‐2,3^+^ cells are able to produce primary alloreactive cytotoxic T lymphocytes (CTL) when incubated with alloantigen alone, but appear to be suppressed in the presence of Lyt‐1,2,3^+^ cells. In contrast, mixtures of Lyt‐2,3^+^ cells selected from C 57 BLI6 T cells previously primed to alloantigen in vitro, and unselected T cells from the Lyt‐2,3‐congenic partner after exposure to the same antigen give rise to cytotoxic effector cells which derive mainly from the primed Lyt‐2,3^+^ cell pool and not from the unselected T cell population. Both populations were able to generate CTL when sensitized separately with the alloantigen. The data suggest that Lyt‐1,2,3^+^ cells contain all primary precursors for both H‐2‐restricted and alloreactive killer cells, as well as lymphocytes suppressing the formation of cytotoxic effector cells from unsensitized Lyt‐2,3^+^ cells. The Lyt‐ 2,3^+^ cell pool most likely contains the secondary CTL precursors. In addition, the same antigen‐primed Lyt‐2,3^+^ pool contains suppressor cells which inhibit the formation of primary CTL from Lyt‐1,2,3^+^ cells. The data are discussed with respect to the regulation of cytotoxic responses.