The guinea-pig complement-activating lymphocyte surface component (GPCA): a mouse T-cell marker distinct from Thy-1

Mouse lymphocytes selectively expressing sensitivity to antibody-independent complement-mediated lysis by normal guinea-pig serum have been previously shown to be identical with T cells. This correlation has raised the question addressed in this work of whether or not the complement-activating surface component and Thy-1 were the same marker. S.49 mouse lymphoblastoid cells, sensitive to killing by anti-Thy-1.2 antibodies plus a source of complement activity devoid of non-specific cytotoxicity, were not sensitive to the non-specific, antibody-independent lytic effects of normal guinea-pig serum. Furthermore, rat thymus cell suspensions containing 93%--95% Thy-1-bearing cells were only partially susceptible (20%--35%) to guinea-pig serum cytotoxicity. Young rat thymus cells virtually devoid of guinea-pig serum-sensitive cells (less than 2%) were readily lysed by antirat Thy-1 and complement (greater than 98%). While these results do not exclude the possibility that Thy-1 may constitute an indirect requirement for T cells to manifest sensitivity to GPS cytotoxicity, it is clear that this antigen does not confer such sensitivity by itself. Therefore, GPCA--the guinea-pig complement-activating marker of murine T cells--is not identical with Thy-1 and represents a distinct surface component of T lymphocytes which manifests itself in terms of a non-specific, but selective ability to activate complement.