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. 2019 Dec 20;8(1):25–37. doi: 10.1016/j.gendis.2019.12.004

Figure 2.

Fig. 2

The TCR interacts with the antigen peptide MHC complex to transmit the first signal of T cell activation. T cells activation also requires paired stimulatory molecules. The interaction of CD28 on T cells with either B7-1 (CD80) or B7-2 (CD86) on APC has been shown to transmit the second signal of T cell activation. The interaction of CD40L on T cells with CD40 on tumor cells has also been shown to transmit the second signal of T cell activation. With the continuous stimulation of tumor antigen on T cells, CTLA-4 is expressed on the surface of T cells. It competes with the CD28 receptor for binding to CD80/CD86 ligands and has a stronger affinity than CD28. CTLA-4 binding to CD80/CD86 inhibits the activation and proliferation of T cells, induces T cell apoptosis, and leads to the immune escape of cancer cells.