Lysis of HIV-infected primary CD4 T cells is mediated by the perforin pathway and is not blocked by fas-blocking antibody. (A) Fas-expressing target cells are sensitive to cytotoxicity induced by fas agonistic antibody CH11. ⁵¹Cr labeled Jurkat cells, 352-BLCL, uninfected PHA-stimulated CD4 blasts, and HIV_IIIB-infected and selected CD4 blasts were exposed to fas agonistic MoAb CH11 in the absence (▪) or presence (⧄) of fas-blocking antibody ZB4. Cytotoxicity was assayed after 6 hours. (B and C) Autologous HIV_IIIB or HXB-nPLAP–infected CD4 T-cell blasts (cultured for 3 days and selected immunomagnetically for HIV expression) and uninfected CD4 T-cell blasts were used as targets for CTL clones directed against the env, gag, nef, and RT proteins of HIV. Target cells were preincubated with EGTA-Mg to block granule-mediated lysis or with fas blocking antibody. Cytotoxicity was assayed at various E:T ratios for clone 352-env52 (B) and at 5:1 for the other clones (C). In (B) the targets are uninfected (□) or infected and incubated with medium (◊), fas blocking antibody (○), or EGTA-MgCl₂ (▵). In (C), targets are uninfected (□) or infected and incubated with medium (▪), fas blocking antibody (⧅) or EGTA (⧄).