Experiments to evaluate the mechanism of cytotoxic action of PBMC subpopulations activated by Hsp70. Cytotoxicity against K562 cells was measured. Each subpopulation was tested alone and in the presence of specific antibodies and inhibitors added 1 h before incubation of target cells with effector lymphocytes. (A) NK cells (CD16+CD56+) and (B) CD3+CD8+ lymphocytes were tested in the presence of antibodies to granzyme B, FasL, NKG2D, and MicA; (C) CD3+CD4+ lymphocytes, in the presence of antibodies to granzyme B, FasL, Tag7 (PGYLRP1), and Hsp70; (D) Hsp70-activated PBMCs were tested for 3 and 24 h in the presence of inhibitors of caspase 3, caspase 8, and RIP1 kinase (Nec1). The data are presented as the mean ± SD of three independent experiments. Asterisks indicate that differences from the control are significant at * p < 0.03 (two-way ANOVA).