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. 2015 Apr 15;10(11):2050–2064. doi: 10.2215/CJN.06620714

Figure 1.

Figure 1.

Activation of effector and regulatory T cells by antigen presenting cells. Key surface molecules in activation of (A) T effector cells and (B) T regulatory cells (Tregs). The key molecules required for both cells are similar. The T cell receptor complex includes CD3, CD2, CD4 or CD8, LFA1, and CD45R, and activation of T cell receptor (TCR) by antigen results in Signal 1 for T effector cells and Tregs. In effector T cell–lineage T cells, CD28 on the T cells is activated by B7.1 and B7.2 on antigen-presenting cells (APCs) and generates Signal 2, which combined with Signal 1, initiates effector T-cell activation. The activation of effector T cells is augmented by CD40L binding to CD40 and cytokines, such as IL-2 and IL-12, for generation of Th1 cells. With Tregs, CTLA4 binds to B7.1 and B7.2 and limits activation through CD28. Thus, the effector T cells Signal 2 pathway is not required for Treg activation. The second signal for Treg activation is generated by IL-2 binding to the IL-2 receptor, which includes CD25.