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. 2017 Oct 11;2017:8415205. doi: 10.1155/2017/8415205

Figure 1.

Figure 1

Costimulation pathways in T cell regulation. Upon MHC-antigen interaction with the TCR, costimulation pathways can augment or suppress the activation of the T cell. From left to right, CD28 is activated by CD80/CD86; however, after T cell activation, CTLA-4 is upregulated and with higher affinity than CD80/CD86 and binds to CD28 inhibiting the signal. CTLA-4Ig and belatacept work by taking advantage of their higher affinity to CD28 over CD80/CD86 and thereby block CD80/CD86 activation of CD28. CD154 and CD40 are other potent activators of T cells; monoclonal antibodies against either of these surface proteins have potential for application in transplant immunosuppression. PD-1 is expressed on T cells, and interaction with PD-1 Ligand (PD-L1) produces a suppressive signal to the T cell.