CTLA-4 inhibition of AICD independent of a CTLA-4 effect on IL-2 production.

(A) CTLA-4 inhibits AICD and IL-2 production in CTLA-4 transfectants. Cells were stimulated with anti-CD3 at a concentration of 0.5 μg/mL and a range of anti–CTLA-4 concentrations from 2 to 10 μg/mL. Supernatants were collected 24 hours after stimulation, and IL-2 levels were determined by ELISA. Anti-TNP control antibody was added to keep the final concentrations equivalent. ▨ indicates IL-2 production; ▪, relative apoptosis. (B) Addition of exogenous IL-2 does not reverse anti–CTLA-4 blockage of AICD. Cells were stimulated with 0.5 μg/mL of anti-CD3 and 10 μg/mL of anti–CTLA-4 with or without recombinant mouse IL-2 (20 U/mL). ■ indicates media; ▪, αCD3; ▨, αCD3 + αCTLA-4; ▧, αCD3 + rIL-2; ▩, αCD3 + αCTLA-4 + rIL-2.