Analysis of phospho-proteins in the MHC class I-signaling pathway in B6.RAG1 KO recipients of BALB/c cardiac allografts following passive transfer of anti-H-2Kd Ab. B6.RAG1 KO mice (n = 32) received fully MHC mismatched cardiac transplants from BALB/c donors. Three days after transplantation, mice were injected with either the anti-H-2Kd IgG Ab (n = 19) or an isotype control IgG Ab (n = 13). Mice were sacrificed on day 15 (n = 13) or 30 (n = 19) and the heart allografts were studied by Western blot for expression of phosphorylated ERK Thr202/Tyr204 (A), S6K Thr421/Ser424 (B), Akt Ser473 (C), S6RP Ser235/236 (D), and mTOR Ser2448 (E). Densitometry results are expressed as the percent maximal increase in phosphorylation divided by total protein (mean ± SE).