Cell‐mediated cytotoxicity against ectromelia virus‐infected target cells. II. Identification of effector cells and analysis of mechanisms

Cell‐mediated cytotoxicity of ectromelia‐immune spleen cells against ectromelia‐infected L929 target cells was abrogated by treatment of the spleen cells with anti‐Θ antibody and complement. Treatment of spleen cells with anti‐immunoglobulin serum and complement, or removal of macrophages had little or no effect on cytotoxicity. Specific or nonspecific soluble cytotoxic factors were not detected, and exogenous interferon did not enhance cytotoxicity. No blocking of cytotoxicity was detected with either hyperimmune or 9‐day immune anti‐ectromelia serum. By varying the spleen cell‐target cell ratio from 3: 1 to 400: 1, it was shown that the efficiency of cytotoxicity was inversely related to spleen cell density. These results were interpreted to mean that thymus‐derived (T) cells, probably acting alone, were responsible for cytotoxicity and that the mechanism involved contact between T cell and target cell.