12, 17, 20 To date, MDSCs are distinguished between two subsets: granulocytic MDSCs have a CD11b+Ly6G+Ly6Clow phenotype, whereas monocytic MDSCs have a CD11b+Ly6G−Ly6Chigh phenotype.17

Thus, IL-10+ BMCs detected in recipient mice share Selisistat the same markers with MDSCs, as specific cells with a nonlobulated nucleus that produce IL-10 (Figs. 3E and 5E). Moreover, recent studies demonstrate that HSCs can promote generation of MDSCs in vivo and in vitro, thereby protecting islet allografts against immune cell attack.12 MDSCs can also increase IL-10 production after cell-cell contact with macrophages of tumor-bearing mice.25 These studies support our results that infiltrated BMCs in fibrotic liver express the same makers as MDSCs, and they further increase IL-10 expression after interacting with activated HSCs. In addition, we found an increased population of CD4+CD25+Foxp3+ Tregs originating from recipient mice after infusion of BMCs that are also anti-inflammatory based on their production of IL-10 and TGF-β (Fig. 2B).15, 18 According to recent studies, MDSCs of patients and mice with tumors contribute to the induction of Tregs.13, 14, 17, 26 Treg induction also requires IL-10 and TGF-β of MDSCs,14 which preferentially induces proliferation of natural Tregs26 leading to

reduced activation of macrophages and T cells. In our study, enhanced IL-10 production of infused BMCs decreased the population of macrophages (Fig. 2C and Supporting Fig. 2D) and PF-01367338 price expanded Tregs in liver MNCs of recipient mice, which was reversed in recipient mice after infusion of IL-10–deficient BMC (Fig. 6D-F). According to previous studies, TGF-β, IL-6, and retinoic acid are not only important factors in T cell differentiation8 but also in the activation

and further differentiation of MDSCs into macrophages, dendritic cells, and granulocytes.14, 19-21 Intriguingly, learn more HSCs can produce a variety of mediators, including TGF-β, IL-6, and retinoic acid, depending on their state of activation.5 Thus, to clarify which mediators of HSCs play an important role in BMC production of IL-10, we cocultured BMCs with HSCs deficient in the production of IL-10, IL-6, and RALDH1 or WT HSCs (Fig. 7A,B). Surprisingly, IL-6–deficient HSCs induced more IL-10 expression by BMCs, whereas RALDH1-deficient HSCs had decreased IL-10 compared with that of BMCs cocultured with WT HSCs. Moreover, RALDH1-deficient mice displayed decreased production of retinoic acid27 and did not show any antifibrotic effects of infused WT BMCs (Fig. 7C,D and Supporting Fig. 6A). However, IL-10–deficient HSCs did not affect production of IL-10 by WT BMCs. Thus, retinoic acid metabolized from retinol by RALDH1 and IL-6 in HSCs might play important roles in IL-10 production by BMCs.