(a)1.Antigen cross-linkage of mlg B7 CD28 (i0 induces signal (which leads to increased expression of class Il MHC and co-stimulatory B7 on B cell. 2.TH cell recognizes antigen-class II MHC on B-cell membrane.This plus co-stimulatory signal activates TH cell CD40 Naive TH cell B cell (b)1.Following activation of TH cell. it begins to express CD-ioL. 2.Interaction of CD40 and CD4OL provides signal② 3.B7-CD28 interactions provide costimulation to the TH cell. B细胞 (c)1.B cell begins to express receptors for various cytokines. 活化的 2.Binding of cytokines released from TH cell in a directed fashion sends 双信号 signals that support the progression of the B cell to DNA synthesis. 途径示 Activated B cell 意图 Mitosis Proliferating B cellsB细胞 活化的 双信号 途径示 意图