Modulation of target cell susceptibility to human natural killer cells by interferon

The spontaneous cytolytic activity of human peripheral blood lymphocytes in a short-term 51chromium release assay was markedly enhanced by pretreatment with partially purified "Namalva" lymphoblastoid (type I) interferon (IF), provided that the target cells, five lymphoblastoid cell lines of variable natural killer (NK) sensitivity (K562, Molt 4, CCRF/CEM, Raji and Bri8), were not similarly treated with IF. When the targets were pre-exposed to comparable concentrations of IF, their susceptibility to lysis by IF-stimulated or unstimulated effectors was diminished, while exposure of both effectors and targets to IF for the duration of the cytotoxicity assay produced levels of cytotoxicity intermediate between those obtained when either effectors or targets were pretreated. The results indicate that, depending on the experimental design. IF is capable of exerting a protective effect on certain targets, a conclusion supported by competition assays wherein IF-treated cold K562 cells competed less successfully than untreated cold K562 cells for lysis of their radiolabelled counterparts by both IF-stimulated and unstimulated effectors. The data suggest that certain lymphoblastoid targets, in common with effector lymphocytes, possess receptors for IF. Some possible biological implications of the protective interaction of IF with tumour targets, which is antagonistic to that on effector cells, are discussed.