Figure 5. Interactions among DCs, Tconvs, and Tregs are necessary for Treg proliferation.
Tconvs are induced to produce IL-2 upon interaction with syngeneic DCs in an MHC class II/TCR and co-stimulatory molecule-dependent manner. This IL-2 in turn binds to the IL-2 receptor (IL-2R) on Tregs and induces their proliferation. IL-2-induced Treg proliferation requires contact with DCs but can occur in an MHC class II– dependent and –independent manner. Co-stimulatory molecules play an important role in the MHC-independent mode of Treg proliferation. The cytokines IL-3 and GMCSF facilitate this process by upregulating MHC class II and co-stimulatory molecule expression by DCs.