Functional analysis of suppression in MLRs. (A) Suppressor cell lines lack significant cytotoxicity for DCs in chromium release assays (•). Control lysis mediated by NK cell line NK92 (▪); 5000 labeled targets were used, with up to a 20:1 effector-target ratio. (B). Suppressor cell lines lack NK or lymphokine-activated killing (LAK)-type activity and show no lytic activity against K562 in chromium release assays (•). Control lysis mediated by NK cell line NK92 (▪); 5000 labeled targets were used, with up to a 20:1 effector-target ratio. (C) In MLR assays, neutralizing antibodies to immunosuppressive factors IL-10 and TGF-β, as well as anti-IL-10R, or combinations of all 3 fail to reverse suppression mediated by cultured suppressor cell lines. (D) Potent suppressor cell lines have minimal inhibitory activity added to MLRs driven by DCs that are autologous to the suppressor (and allogeneic to the responder). Suppressor cell line Ts-A (▤) was used to suppress MLR cultures driven by DC-A (from the same donor as the suppressor) or by DC-B (from a different donor from suppressor). Suppressor cell line Ts-B (checkered bars) was also tested against DC-A and DC-B. Representative of 4 experiments.