Disappearance of the NK effect after explantation of lymphocytes and generation of similar nonspecific cytotoxicity correlated to the level of blastogenesis in activated cultures

We compared the characteristics of NK and the killer lymphocytes activated in various stimulation systems. Lymphocytes were cultured for 6 days in FCS, in mixed cultures with K562 (MKC) or with allogeneic lymphocytes (MLC) or kept with mitogenic factor (MF) present in the supernatant of PHA-stimulated lymphocytes. The cytotoxic potential generated in these cultures was proportional to the level of activation, evaluated by proliferation and blast transformation. The activated lymphocyte killing (ALK) was as efficient against the NK-sensitive K562 as against Daudi cell line, shown to be almost insensitive to fresh NK in short-term test. Lymphocytes cultured alone in autologous plasma (AP) lost NK activity. In MLC the kinetics of appearance of the newly generated activity against the two cell lines was similar and peaked at day 6. In cold target competition tests, Daudi cells competed partially for the anti-K562 effect of the MKC populations. In MLC, the level of anti-K562 and anti-Daudi killing did not parallel the efficiency of allospecific CTL. Cells cultured with MF had strong ALK already after 2 days. The majority of the cells growing in the presence of MF rosetted with SRBC. On the basis of these and previous results in MKC, MLC, and autologous stimulation (AS) systems, we conclude that ALK is a property of activated T lymphocytes; it is not due to the survival of the NK activity, but is newly generated in vitro. The characteristics of NK and ALK effectors are somewhat different.