K562 killing by K, IL 2-responsive NK, and T cells involves different effector cell post-binding trigger mechanisms.

The monoclonal antibody 13.3 specifically blocks the trigger process of the NK-K562 cytolytic sequence at a post-binding effector cell level. This antibody was used to define differences in the lytic trigger processes of NK and other mechanisms of K562 lysis. Monoclonal antibody 13.3 inhibited lysis of K562 target cells by freshly isolated peripheral blood lymphocytes (PBL) and purified large granular lymphocytes (LGL), but had no inhibitory effect on antibody-dependent cell-mediated cytotoxicity to K562 by these effectors. Lectin-dependent cellular cytotoxicity (LDCC) to this target cell was also unresponsive to 13.3. The 13.3-induced inhibition of NK-K562 lytic activity persisted when PBL were activated in culture with interleukin 2 (IL 2) for periods up to 48 hr. After 48 hr of culture, the degree of inhibition diminished progressively in medium containing fetal calf serum but not in medium containing autologous serum. This 13.3-unresponsive lytic activity in cultured PBL could be attributed to more than one cell type and was present in both the LGL and Fc gamma receptor-depleted T cell fraction. Thus, K562 lysis by freshly isolated human lymphocytes via NK, K, and LDCC mechanisms is characterized by heterogeneity of the post-binding effector cell trigger mechanism. K562 lysis by lymphocytes cultured with IL 2 is similarly heterogeneous.