Figure 4.

Alloantigen-primed PKH-26^dim CBTL have defective Ras activation after restimulation with CD3 plus CD28. Ras can be activated in PKH-26^dim CBTL by treatment with PMA plus ionomycin. The ability of freshly isolated CBTL to activate Ras during primary allostimulation is shown (CB 1^o Allo), indicating that defective Ras activation develops in PKH-26^dim CBTL only after a primary proliferative response. PKH-26^dim PBTL, PKH-26^bright CBTL, and PKH-26^bright PBTL show normal Ras activation. Similar results were obtained when either alloantigen or antibodies were used for both primary and secondary experiments (data not shown). Control IP, immunoprecipitation with rat anti-mouse Ig.