LFA-1 but not Lyt-2 is associated with killing activity of cytotoxic T lymphocyte hybridomas

Abstract

The mechanism by which cytotoxic T lymphocytes (CTL) recognize and lyse target cells is largely unknown. Recently, two lymphocyte cell-surface glycoproteins, Lyt-2^1–4 and LFA-1 (lymphocyte function-associated antigen)^5–8, have been implicated in the killing activity of murine CTL. This suggestion was based mainly on the unique ability of antibodies directed against Lyt-2^1–4 and LFA-1^5–8 to inhibit cytotoxicity of CTL by affecting the killer cell. Lyt-2, a glycoprotein composed of subunits of molecular weights of 30,000–35,000 (30–35K), has been proposed as a common marker for CTL⁹, essential for specific recognition of target cells¹⁰. This view, however, is incompatible with other results^11–14. The newly detected LFA-1 molecule, containing subunits of 95K and 180K^5–8,15, is associated with the ability of CTL to bind target cells^16,17. Most analyses of CTL structure–function relationships are ambiguous since they have been obtained with heterogeneous CTL populations. We have recently developed CTL-hybridomas which lyse specifically allogeneic tumour cells in vitro¹⁸ and grow independently of exogenous stimuli¹⁹. In this study we have tested the relevance of Lyt-2 and LFA-1 antigens to cytotoxicity by analysing the CTL-hybridomas with a panel of anti-LFA-1 and anti-Lyt-2 monoclonal antibodies. We show that two monoclonal CTL-hybridomas have the phenotype LFA-1⁺ and Lyt-2⁻ and that their killing activity is inhibited by anti-LFA-1 but not by anti-Lyt-2. The results suggest that LFA-1 is involved in CTL-cytotoxicity, while Lyt-2 molecules are not required.