Clonal heterogeneity in the functional requirement for Lyt-2/3 molecules on cytolytic T lymphocytes: analysis by antibody blocking and selective trypsinization.

Abstract

While it is well established that murine cytolytic T lymphocytes (CTL) express the Lyt-2/3 molecular complex on their surface, conflicting results have been reported concerning the role of this complex in CTL activity. This question was reinvestigated at the clonal level. Although different (H-2b anti-H-2d) CTL clones expressed comparable amounts of Lyt-2/3 molecules, as assessed by quantitative flow microfluorometry, the activity of some clones was inhibited by low doses (10 ng) of monoclonal anti-Lyt-2 or anti-Lyt-3 antibodies (in the absence of complement), whereas other clones were not inhibited by either antibody at doses as high as 5 .mu.g. Treatment of these clones with doses of trypsin sufficient to cleave Lyt-2/3 antigenic determinants from the cell surface resulted in a similar dissociation: clones that were inhibited by antibodies lost cytolytic activity, whereas uninhibited clones were unaffected by trypsin treatment. The dissociation observed among different alloreactive clones could be demonstrated within self-H-2-restricted (H-2b anti-MSV) clones exhibiting cross-reactivity with normal H-2d products. The lytic activity of these clones against the relevant syngeneic target cells was unaffected by anti-Lyt-2 antibodies or trypsin, whereas their cross-reactivity on H-2d target cells was abolished by either treatment. The results provide direct evidence for clonal heterogeneity in the requirement for Lyt-2/3 molecules in CTL-mediated lysis. The function of Lyt-2/3 molecules probably to stabilize the interaction between CTL receptors and the corresponding antigens on the target cells. The requirement for such a stabilization is apparently correlated with low number and/or affinity of CTL receptors.