Modulation of stimulatory effects of poly(I:C) on natural cytotoxicity by anti-interferon.

The effect of polyinosinic . polycytidylic acid [poly(I:C)] on tumor inhibition in the context of natural cytotoxicity enhancement prompted further assessment of mechanisms underlying these effects. In vivo inoculations of poly(I:C) led to dose-dependent cytotoxicity enhancement in splenic lymphocytes and nonrecruited peritoneal exudate cells (monocytes). Although cytotoxicity of macrophages and lymphocytes together was less than that seen with lymphocytes alone, addition of indomethacin to these samples did not enhance cytotoxicity. In vivo inoculation of anti-interferon prior to poly(I:C) treatment prevented poly(I:C)-induced enhancement of natural cytotoxicity. Tumor growth was significantly inhibited by poly(I:C) treatment. Prior inoculation of anti-interferon antiserum partially prevented such tumor inhibition. Taken together, the tumor-inhibitory effect of poly(I:C) in this model may be mediated by interferon production and, at least in part, by interferon-induced enhancement of natural cytotoxicity.