Cytokine receptor 4 CD④ ntigen Co-Stimulatory IL-2 Signal TH activation Effecto APC Class II TH cell dendritic celD MHC Memory T cell TH cells receptor IL-2 IL-2 冖细胞的分化 Antigen IL2 Class I MHC B cel Cytokines TH cell TC ce cDs Altered self cell Memory B cell Plasma cell Memory Tc cell Killing CTL LysisT B 细胞的分化