Tim-3(+) decidual Mφs induced Th2 and Treg bias in decidual CD4(+)T cells and promoted pregnancy maintenance via CD132

T-cell immunoglobulin mucin-3 (Tim-3) plays roles in the functional regulation of both adaptive and innate immune cells and is greatly involved in many diseases. However, the precise roles of Tim-3 on macrophages (Mφs) in pregnancy remain unstated. In the current study, we found the higher frequency of Tim-3(+) decidual Mφs (dMφs) in response to trophoblasts. The reduced abundance of Tim-3 on Mφs was accompanied by disordered anti- and pro-inflammatory cytokine profiles in miscarriage. Adoptive transfer of Tim-3(+)Mφs, but not Tim-3(−)Mφs, relieved murine embryo absorption induced by Mφ depletion. Our flow cytometry results and the extensive microarray analysis confirmed that Tim-3(+) and Tim-3(−)dMφs were neither precisely pro-inflammatory (M1) nor anti-inflammatory (M2) Mφs. However, with higher CD132 expression, Tim-3(+)dMφs subset induced Th2 and Treg bias in decidual CD4(+)T cells and promoted pregnancy maintenance. Blockade of Tim-3 or CD132 pathways leaded to the dysfunction of maternal-fetal tolerance and increased fetal loss. These findings underscored the important roles of Tim-3 in regulating dMφ function and maintaining normal pregnancy, and suggested that Tim-3 on Mφs is a potential biomarker for diagnosis of miscarriage. Our study also emphasized the importance of careful consideration of reproductive safety when choosing immune checkpoint blockade therapies in real world clinical care. Though IL-4 treated Tim-3(−)Mφs could rescue the fetal resorption induced by Mφ depletion, whether IL-4 represent novel therapeutic strategy to prevent pregnancy loss induced by checkpoint inhibition still needs further research.