"Self-reactive" T cells. II. Transferred syngeneic lymphoblasts induce T "stimulator" cells in vivo, to which syngeneic T cells "respond" in a syngeneic MLC in vitro.

Splenic T cells, engaged in an in-vivo "response" to transferred syngeneic lymphoblasts, displayed an extensive proliferative activity if cultured in vitro. These cells (blocked by mitomycin C) were "stimulator" cells in a one-way syngeneic mixed lymphocyte culture (S-MLC). "Responder" cells were derived form spleens of syngeneic (sex and age matched) mice. Fractionation studies showed that "stimulator" and "responder" cells in the investigated S-MLC were nylon-wool non-adherent and sensitive to treatment with anti-Thy-1 antiserum and complement, i.e. were cells of the T lineage. Coculture experiments demonstrated that direct cell contact is required to trigger a proliferative "response" in the S-MLC. Fetal calf serum-supplemented tissue-culture medium supported "responder" cell proliferation, normal mouse serum-supplemented medium did not. The in-vivo generation of a T-cell population, which could "stimulate" a syngeneic T-cell "response" in the S-MLC in vitro, was investigated.