Phosphorylation of PD-1 and BTLA in SHP1 KO or SHP1/2 DKO Jurkat cells. (A) IBs showing the phosphorylation and SHP2 association of PD-1–mGFP or BTLA-mGFP immunoprecipitated from the lysates of the indicated co-cultures, with the stimulation time indicated (see Materials and methods). GFP IB indicates the input of PD-1–mGFP or BTLA-mGFP. (B) Same as A, except using SHP1/2 DKO Jurkat cells instead of SHP1 KO Jurkat cells.