Expression of Qat‐4 and Qat‐5 alloantigens on cytotoxic precursor and effector cells: different surface phenotypes of alloreactive and H‐2‐restricted cytotoxic T Cells

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Abstract
Monoclonal anti-Qat-4 and anti-Qat-5 antibodies, which define antigens expressed on peripheral T cell subsets, were used to study the phenotypes of alloreactive and H-2-restricted [mouse] cytotoxic effector cells and their precursors. Depletion of Qat-4+ or Qat-5+ cells from the T cell pool prior to their sensitization in bulk cultures prevented the development of alloreactive and H-2-restricted cytotoxic activities in the selected populations. No reconstitution of cytolytic activities to normal levels was obtained when mixtures of Qat-4- and Qat-5- cells were sensitized in bulk cultures to H-2 or non-H-2 antigens. Sensitization of limiting numbers of Qat-4- or Qat-5- lymphocytes under optimal conditions for help (interleukin 2), with the appropriate antigens (H-2, H-Y), did not result in the generation of cytotoxic T cells, indicating that the majority of all cytotoxic T lymphocyte (CTL) precursors are Qat-4+, Qat-5+. When CTL effector populations were treated with the antisera and complement (C) at their maximum CTL activity, H-2-restricted CTL were totally eliminated by anti-Qat-4 and considerably reduced by anti-Qat-5 antisera and C. Alloreactive CTL effector cells were insensitive to anti-Qat-4 and to anti-Qat-5 plus C. Although alloreactive CTL effector populations regained some Qat-4 antigens during further in vitro culture, H-2-restricted CTL were at all times more sensitive to anti-Qat-4 than were alloreactive CTL. During maturation of alloreactive and H-2-restricted CTL from their precursors, both alloantigens probably undergo differential quantitative variations in their expression that lead to different Qat-4,5 phenotypes of alloreactive and H-2-restricted CTL.

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