The Fifth Epidermal Growth Factor–like Region of Thrombomodulin Alleviates Murine Graft-versus-Host Disease in a G-Protein Coupled Receptor 15 Dependent Manner

Abstract

Thrombomodulin (TM) exerts anti-inflammatory functions. We previously found that recombinant human soluble TM alleviated murine graft-versus-host disease (GVHD). Nevertheless, it is unclear how TM mediates its anti-inflammatory functions in GVHD. Here, we identified G-protein coupled receptor 15 (GPR15) expressed on T cells as a receptor/sensor of TM. The fifth region of epidermal growth factor–like domain of TM (TME5) bound GPR15 in vitro. TME5 prolonged survival of mice undergoing acute GVHD after allogeneic hematopoietic stem cell transplantation (allo-HSCT). TME5 increased regulatory T cells (Tregs) but decreased Th 1 proportions in targeted organs. TME5 suppressed allo-reaction in vitro in association with an increase in the number of induced Tregs. However, the anti-inflammatory function of TME5 was abolished when GPR15 knockout T cells were used as donor T cells. We further found that TME5 suppressed production of IL-6 in T cells, which probably facilitated differentiation of Tregs. Moreover, TME5 reduced activation of bone marrow–derived dendritic cells (BMDCs) and hampered function of BMDCs in inducing allo-reaction in vivo and in vitro. Our findings suggested that inducing Tregs as well as blocking activation of DCs in vivo by using TME5 is a potential therapeutic option for preventing GVHD in allo-HSCT.