Characterization of Monoclonal Antibodies Against Cell Surface Molecules Associated with Cytotoxic Activity of Natural and Activated Killer Cells and Cloned CTL Lines

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Abstract
Supernatants of hybridomas from fused spleen cells of mice immunized with either a T4+ or a T8+ CTL [cytotoxic T-lymphocyte] clone were screened for their ability to inhibit the cytotoxic activity of the T4+ and the T8+ CTL clone. Eight monoclonal antibodies (MAb) with blocking activity were obtained and a preliminary characterization of these antibodies was carried out. The MAb SPV-L1 and SPV-L5 reacted with thymocytes and all peripheral blood leukocytes. SPV-L1 and SPV-L5 precipitated a molecular complex consisting of 2 noncovalently bound chains of MW of 95 and 160 kD [kiloDalton] indicating that they recognize the human equivalents of the recently described leukocyte function associated (LFA-1) antigens. The SPV-L1 and SPV-L5 antibodies inhibited the reactivity of 6 CTL clones tested in this study. SPV-L1 and L5 blocked the lectin dependent cellular cytotoxicity mediated by these CTL clones. Natural killer cell activity mediated by fresh peripheral blood lymphocytes and activated killer cell activity generated in MLC [mixed lymphocyte culture] both measured against K562 [human leukemia cells] was also inhibited by SPV-L1 and SPV-L5. Two other antibodies, SPV-L3 and SPV-L4, blocked strongly the cytotoxic activity of 2 T4+ CTL clones while the reactivity of the 3 T8+ CTL clones and 1 T4+ CTL clone was not or only moderately inhibited. These antibodies recognized an Ia antigen as judged from tissue distribution and immunoprecipitation studies. These latter studies also suggest that SPV-L3 and SPV-L4 recognize HLA-DC rather than HLA-DR antigens. Three antibodies (SPV-T3a, SPV-T3b, SPV-T3c) were obtained directed against the T3 molecular complex and 1 MAb (SPV-T8) reacted with T8. The anti-T3 reagents were mitogenic for peripheral blood lymphocyts, with the exception of SPV-T3a. Evidently, the antigens recognized by SPV-L1 and SPV-L5 are involved in various cytotoxic reactions. SPV-L3, SPV-T3 and SPV-T8 only seem to play a role in antigen specific cytotoxic reactions.