B7.-CD28 VERSUS B7---CTLA-4 (3t CO4 NCD4 T CELL TCR SIGNALPACTIVATION ARMED B7 SIGNAL 2 EFFECTOR CD28 Th CELL SIGNAL TCR I DOWN- REGULATION ACTIVATION BLOCKED OF T CELL B7 RESPONSE SIGNAL CTLA-42021年2月5日星期五9 时17分11秒