Figure 1.

Regulatory T cells (Tregs) are present in the host at the time of transplantation and are recruited to the allograft. They respond to donor alloantigen through cross-reactivity and inhibit T-cell proliferation in draining lymphoid tissue. Tolerogenic DCs favor the generation of Tregs from naive T cells, which then block effector T-cell proliferation while also triggering apoptosis of these cells. They inhibit TH1 cells. These processes facilitate allograft acceptance through several mechanisms including the production and release of immunosuppressive cytokines, such as IL-10 and TGFβ (modified from Wood et al. [2]).