CTLA-4 interacts with PP2A in primary human T cells and Jurkat T cells. A) PBMC were isolated from healthy donors and cultured in the presence of PMA (1 ng/ml) and ionomycin (100 ng/ml) for 72 h. The cells were washed extensively and rested for 24 h in fresh media. Cell lysates were immunoprecipitated using anti-CTLA-4 Abs and immunoblotted for CTLA-4, PP2AA and PP2AC. B) Jurkat T cells stably transfected with WT CTLA-4 were cultured overnight in the presence of doxycycline (1 μg/ml) to induce the expression of CTLA-4. Cell lysates were immunoprecipitated and immunoblotted as in A).