title: Inhibitory factors derived from human tumors: isolation of factors which suppress macrophage mediated cytotoxicity.
abstract: Previously, we had demonstrated that plasma inhibitory factors obtained from colon cancer patients suppressed macrophage mediated cytotoxicity. When this inhibitor was further purified, four fractions (A, B, C and D) with inhibitory activity were isolated. In this study, it was found that these four purified inhibitory factors also dramatically decreased the extent of macrophage mediated cytotoxicity induced by LPS when added during the activation phase of the assay. When the secretions from a variety of fresh tumors as well as several established tumor cell lines were purified utilizing immunoadsorbent techniques, those same inhibitory factors were recovered. It was found that 8 of the 11 secretions obtained from a variety of fresh tumors and established tumor cell lines secreted inhibitor A; 6 secreted inhibitor B and 5 secreted inhibitor C. (The presence of inhibitor D was not studied.) Furthermore, one of the 11 tumors studied secreted none of these inhibitory factors. These findings lend support to the theory that these inhibitory factors which are initially produced by the tumor and subsequently shed into the sera ultimately lead to in vivo suppression of macrophage mediated cytotoxicity.
mesh_terms: D001202:Ascitic Fluid / Q000473:pathology*; D003602:Cytotoxicity, Immunologic / Q000187:drug effects; D006801:Humans; D007108:Immune Tolerance; D007111:Immunity, Cellular / Q000187:drug effects; D008264:Macrophages / Q000276:immunology*; D009369:Neoplasms / Q000276:immunology*