One of the main unresolved questions in solid organ transplantation is how to establish indefinite graft survival that is free from long-term treatment with immunosuppressive drugs and chronic rejection (i.e., the establishment of tolerance). The failure to achieve this goal may be related to the difficulty in identifying the phenotype and function of the cell subsets that participate in the induction of tolerance. To address this issue, we investigated the suppressive roles of recipient myeloid cells that may be manipulated to induce tolerance to transplanted hearts in mice. Using depleting mAbs, clodronate-loaded liposomes, and transgenic mice specific for depletion of CD11c + , CD11b + , or CD115 + cells, we identified a tolerogenic role for CD11b + CD115 + Gr1 + monocytes during the induction of tolerance by costimulatory blockade with CD40L-specific mAb. Early after transplantation, Gr1 + monocytes migrated from the bone marrow into the transplanted organ, where they prevented the initiation of adaptive immune responses that lead to allograft rejection and participated in the development of Tregs. Our results suggest that mobilization of bone marrow CD11b + CD115 + Gr1 + monocytes under sterile inflammatory conditions mediates the induction of indefinite allograft survival. We propose that manipulating the common bone marrow monocyte progenitor could be a useful clinical therapeutic approach for inducing transplantation tolerance.

IL-10 production by Th17 cells is critical for limiting autoimmunity and inflammatory responses. Gene array analysis on Stat6 and T-bet double-deficient Th17 cells identified the Th2 transcription factor c-Maf to be synergistically up-regulated by IL-6 plus TGFβ and associated with Th17 IL-10 production. Both c-Maf and IL-10 induction during Th17 polarization depended on Stat3, but not Stat6 or Stat1, and mechanistically differed from IL-10 regulation by Th2 or IL-27 signals. TGFβ was also synergistic with IL-27 to induce c-Maf, and it induced Stat1-independent IL-10 expression in contrast to IL-27 alone. Retroviral transduction of c-Maf was able to induce IL-10 expression in Stat6-deficient CD4 and CD8 T cells, and c-Maf directly transactivated IL-10 gene expression through binding to a MARE (Maf recognition element) motif in the IL-10 promoter. Taken together, these data reveal a novel role for c-Maf in regulating T effector development, and they suggest that TGFβ may antagonize Th17 immunity by IL-10 production through c-Maf induction.

Th1 and Th17 cells are crucial in immune regulation and autoimmune disease development. By adding Stat6 deficiency to T-bet deficiency, and thus negating effects from elevated levels of IL-4/Stat6/GATA3 Th2 signals in T-bet-deficient cells, we investigated the signals important for Th1 and Th17 cell differentiation and their role in colitis development. The data reveal that Eomesodermin compensates T-bet deficiency for IFN-γ and Th1 development. However, without T-bet, IFN-γ production and Th1 differentiation are susceptible to inhibition by IL-6 and TGFβ. As a result, Th17 development is strongly favored, the threshold for TGFβ requirement is lowered, and IL-6 drives Th17 differentiation, elucidating a critical role for T-bet in directing T cell differentiation to Th1 vs Th17. In contrast to IL-6 plus TGFβ-driven Th17, IL-6-driven Th17 cells do not express IL-10 and they induce a more intense colitis. Naive CD4 T cells deficient in Stat6 and T-bet also induce a Th17-dominant colitis development in vivo. Our data provide new insights into the choice between Th1 and Th17 development and their roles in autoimmunity.

CD4+CD25+Foxp3+ regulatory T (Treg) cells migrate into both inflammatory sites and draining lymph nodes (LNs) during an immune response, and have unique and overlaping functions in each location. Current studies suggest that Treg cells in draining LNs and inflamatory sites may not simply be a division of labor, rather Treg migrate in a coordinated fashion between peripheral tissues and draining LNs. Trafficking between inflammatory sites and draining LNs is not only critical for Treg to act, but also for them to acquire optimal immune regulatory activities. Furthermore, recent work has revealed that T helper (Th) 1, Th2, and Th17 master transcription factors, control Treg function by regulating genes important for Treg migration and suppression, and consequently affecting disease pathogenesis.

Background Lymphatics are important for their conduit functions of transporting antigen, immune cells, and inflammatory mediators to draining lymph nodes and to the general circulation. Lymphangiogenesis is involved in many pathologic processes; however, the roles for lymphatic responses in transplantation have not been thoroughly investigated. Methods Mice were made diabetic by a single high dose of streptozotocin and then received islet allografts. Animals were treated with three different lymphatic inhibitors. FTY720, an analog of sphingosine 1-phosphate, inhibited lymphocyte migration into afferent and efferent lymphatics. Sunitinib, a kinase inhibitor, blocked several receptors, including vascular endothelial growth factor receptor 3 (VEGFR3), the major growth factor receptor for lymphatic endothelial cells. Anti-VEGFR3 monoclonal antibody specifically inhibited VEGFR3. Diabetes was determined by daily monitoring of blood glucose levels. Inflammation within islet grafts was assessed by immunohistochemistry for insulin, T cells (CD3), and lymphatics (LYVE-1). Results After transplantation, lymphangiogenesis occurred in islet allografts and in draining lymph nodes. FTY720, sunitinib, and anti-VEGFR3 each inhibited lymphangiogenesis in the islets and significantly prolonged allograft survival. Immunofluorescent staining demonstrated that administration of each of the lymphatic inhibitors resulted in preservation of islets and β-cells along with a markedly reduced infiltration of T cells into the grafts. Conclusion Lymphangiogenesis occurs in islet allografts in response to inflammation and plays a key role in the islet inflammation in alloimmunity. Interfering with lymphatic function leads to inhibition of lymphangiogenesis and prolonged or indefinite allograft survival. These observations suggest new therapeutic targets for rejection and tolerance.