Cytotoxic T cells: Lyt phenotype and blocking of killing activity by Lyt antisera

WE REEXAMINED TWO QUESTIONS CONCERNING LYT ANTIGENS OF CYTOTOXIC T CELLS OF THE MOUSE: is Lyt-1 antigen expressed on cytotoxic effector cells and can cytotoxicity be blocked by antibody to Lyt antigens in the absence of added complement? A 3-hr (51)Cr-release assay with splenic effector cells and leukemia or myeloma target cells was used to measure cell-mediated cytotoxicity. The cytotoxic activity of effector cells against allogeneic targets was abolished by exposure to Lyt-1, Lyt-2, or Lyt-3 antiserum and complement. Specificity was established by tests with C57BL/6 Lyt congenic mice and absorption studies with thymocytes. Similarly, the cytotoxicity of effector cells directed against semisyngeneic myeloma targets was reduced by Lyt-1, -2, or -3 antiserum and complement. Effector cell cytotoxicity against another semisyngeneic target was only marginally affected by Lyt-1 antiserum and complement, but was abolished by Lyt-2 or -3 antiserum and complement. It appears likely that cytotoxic T cells are a heterogeneous population with regard to Lyt-1 expression and that past studies indicating an apparent absence of Lyt-1 on cytotoxic T cells revealed a quantitative, not qualitative, feature of these cells. With regard to the activity of Lyt antisera in the absence of added complement, selective blocking of effector cell cytotoxicity for allogeneic and semisyngeneic targets was found with Lyt-2 and Lyt-3 antisera but not with Lyt-1 antiserum. The specificity of blocking was established by tests with Lyt congenic mice and absorption studies with thymocytes. With the exception of blocking by antisera to the H-2 haplotype expressed by the target cell, no effector cell blocking was observed with alloantisera or heteroantisera to a range of other cell surface molecules present on mouse lymphoid cells. One possibility to account for the selective blocking by Lyt-2 and Lyt-3 antisera is that Lyt-2,3 determinants on the surface of cytotoxic T cells have a close spatial relation to the T cell receptor.