In addition, several studies have indicated that the in vivo function of Tregs is dependent on their migration into sites of inflammation 16–19. Selleck CHIR 99021 Although compartmentalization of Tregs is not a new phenomenon 20, the concept that Tregs migrate into allografts and inhibit rejection is a very recent observation 16–18, 21. An emerging model is that tolerance to alloantigens can only be achieved if Tregs are allowed to migrate in an appropriate pattern within allografts and within lymph

nodes 16, 18. It has been reported that Tregs express multiple chemokine receptors 22; some studies have identified that the majority of human Tregs express CD62L 23, CCR4 22, 24 and CCR7 25. These combinations should allow Tregs to migrate into lymph nodes and into the periphery. Nevertheless, most studies have been performed in rodents 18, 20, 24, and few studies have evaluated expression of these receptors in human Treg subsets. The CXC chemokine receptor 3 (CXCR3) is classically expressed on activated human CD4+ T cells, and is well

established to mediate effector cell trafficking 26–28. Consistent with these findings, the expression of CXCR3 28–30 and its chemokine ligands, monokine induced by IFN-γ (Mig or CXCL9), IFN-γ-inducible protein Fulvestrant mw of 10 kDa (IP-10 or CXCL10) and IFN-γ-inducible T-cell α-chemoattractant (or CXCL11) have been reported to be associated with both cardiac and renal allograft rejection 28, 30–37. However, paradoxically, some recent studies have suggested that CXCR3 may also be expressed on Tregs 22, 38–41, and blockade of CXCR3 is reported to have variable functional effects in different animal models 32, 42, 43. Nevertheless, little is known about its expression pattern or its association with Treg subsets and their immunoregulatory function(s). In this study, we characterized the expression of CXCR3 on human CD25hi FOXP3+ CD4+ T regulatory cells, and we demonstrate that CXCR3hi Tregs are functional to suppress effector Aprepitant alloimmune responses. Furthermore, we demonstrate that levels of CXCR3 increase on Tregs following activation, and that CXCR3hi Tregs are enriched in cell culture

in the presence of rapamycin. We initially analyzed the co-expression of CXCR3 and CD25 on CD4+ T cells by four color flow cytometry. Consistently, we observed two subpopulations of CD25hi cells that were either CXCR3hi or CXCR3lo/neg (Fig. 1A). As illustrated in Fig. 1B and C, we also found that FOXP3 was expressed within both populations and, further, that the level of FOXP3 expression in each subset was similar. We gated on CD25hi, CD25int/lo and CD25neg CD4+ T-cell subsets, and we assessed the relative expression of CXCR3 on each population. As illustrated in Fig. 2A, we found that CXCR3 is expressed by all subsets, irrespective of CD25 expression; but notably, double positive CXCR3+CD25hi populations co-express significant levels of FOXP3.