Studies on cytotoxicity generated in human mixed lymphocyte culture. IV. Interleukin 2 alone or from mixed lymphocyte culture yields natural killer-like cytotoxic cells distinct from allospecific cytotoxic T lymphocytes.

High levels of cytotoxic activity against the natural killer (NK) cell-sensitive target K562 and the NK-resistant target UCLA-SO-M14 (M14) can be generated in vitro either by mixed lymphocyte culture (MLC) or by culture of lymphocytes in interleukin 2 (IL2) (lymphokine activated killer (LAK) cells). The purpose of this study was to identify similarities and differences between MLC-LAK and IL2-LAK cells and allospecific cytotoxic T cells. Induction of cytotoxicity against K562 and M14 in both culture systems was inhibited by antibodies specific either for IL2 or the Tac IL2 receptor. Like NK effector cells, the precursors for the MLC-LAK cells were low density large lymphocytes. However these precursors differed from the large granular lymphocytes that mediated NK cytolysis in sensitivity to the toxic lysosomotropic agent L-leucine methyl ester (LME). The resistance of the MLC-LAK precursors to LME indicated that the precursors included large agranular lymphocytes. Although interferon-gamma (IFN-gamma) is produced in MLC and in IL2 containing cultures, it is not required for induction of either type of cytotoxic activity. Neutralization of IFN-gamma in MLC- and IL2-containing cultures with specific antibodies had no effect on the induction of cytotoxic activities. Both allospecific cytotoxic T lymphocyte (CTL) and LAK activities were enhanced by IL2 and IFN-gamma at the effector cell stage. However, the mechanism of cytolysis was different in the two systems. NK- and MLC-induced LAK activities were independent of CD3-T cell receptor complex while CTL activity was blocked by monoclonal antibodies specific for the CD3 antigen. These results suggest that NK and the in vitro induced LAK cytotoxicities are a family of related functions that differ from CTL. Furthermore, MLC-induced and IL2-induced cytotoxicities against K562 and M14 appear to be identical.