CCR2 enhances CD25 expression by FoxP3^(+) regulatory T cells and regulates their abundance independently of chemotaxis and CCR2^(+) myeloid cells

A wide array of chemokine receptors,including CCR2,are known to control Treg migration.Here,we report that CCR2 regulates Tregs beyond chemotaxis.We found that CCR2 deficiency reduced CD25 expression by FoxP3^(+) Treg cells.Such a change was also consistently present in irradiation chimeras reconstituted with mixed bone marrow from wild-type(WT)and CCR2−/−strains.Thus,CCR2 deficiency resulted in profound loss of CD25 ^(hi) FoxP3^(+) Tregs in secondary lymphoid organs as well as in peripheral tissues.CCR2−/−Treg cells were also functionally inferior to WT cells.Interestingly,these changes to Treg cells did not depend on CCR2+monocytes/moDCs(the cells where CCR2 receptors are most abundant).Rather,we demonstrated that CCR2 was required for TLR-stimulated,but not TCR-or IL-2-stimulated,CD25 upregulation on Treg cells.Thus,we propose that CCR2 signaling can increase the fitness of FoxP3^(+) Treg cells and provide negative feedback to counter the proinflammatory effects of CCR2 on myeloid cells.