Gross-virus-induced lymphoma in the rat. IV. Cytotoxic cells in normal rats.

Lymphoid cells from normal W/Fu rats are cytotoxic in vitro for syngeneic Gross-virus-induced lymphoma cells in a 4 1/2 h 51Cr release test, and protect against tumour growth in vivo when adoptively transferred to syngeneic recipient rats. Cytotoxicity by normal lymphoid cells was greater with in vitro rather than in vivo passaged target cells, and was increased by preincubation of the lymphoid cells at 37 degrees C for 3 h in vitro before their addition to the target cells. Cytotoxic activity, which was localized predominantly in the spleen, was absent at birth but increased until adulthood with some decline in older age. Histocompatibility at the major Ag-B locus was not required for the killer cell--target cell interaction; normal spleen cells of many Ag-B genotypes were cytotoxic for W/FuG-1 target cells, although BDIX and (BDIX X W/Fu)F1 were less active and BN were inactive. The specificity of cytotoxicity was studied by the techniques of direct lysis, competitive inhibition or adsorption to cellular monolayers, using a variety of cell lines. Selectively of lysis or binding was observed and was restricted to rat target cells releasing exogenous or endogenous C-type viruses.