T CELL ACTIVATION:T CELL CHANGES CD45RA RESTING IL-2R LOW AFFINITY "NAIVE RECEPTOR FOR IL 2 CD4 T CELL IL-2R BETA CHAIN IL-2R GAMMA CHAIN T CELL ACTIVATION CD4SRO CTLA 4 WITH EXERESSON OEIL2R ALPHA CHAIN HIGH AFFINITY RECEPTOR FOR IL-2 CLASS II MHC TRIGGERS: PROLIFERATION -2 ACTIVATED "ARMED CYTOKINES TYPICAL OF CD4 T CELL Th1 or Th2 CELLS