Macrophages characterized as M2 and M2-like regulate immune responses associated with immune suppression and healing; however, the relationship of this macrophage subset to CD169+ tissue-resident macrophages and their contribution to shaping alloimmune responses is unknown. Here we identified a population of M2-like tissue-resident macrophages that express high levels of the phosphatidylserine receptor TIM-4 and CD169 (TIM-4hiCD169+). Labeling and tracking of TIM-4hiCD169+ macrophages in mice revealed that this population is a major subset of tissue-resident macrophages, homes to draining LNs following oxidative stress, exhibits an immunoregulatory and hypostimulatory phenotype that is maintained after migration to secondary lymphoid organs, favors preferential induction of antigen-stimulated Tregs, and is highly susceptible to apoptosis. Moreover, CD169+ tissue-resident macrophages were resistant to oxidative stress–induced apoptosis in mice lacking TIM-4. Compared with heart allografts from WT mice, Tim4–/– heart allografts survived much longer and were more easily tolerized by non-immunosuppressed recipients. Furthermore, Tim4–/– allograft survival was associated with the infiltration of Tregs into the graft. Together, our data provide evidence that M2-like TIM-4hiCD169+ tissue-resident macrophages are immunoregulatory and promote engraftment of cardiac allografts, but their influence is diminished by TIM-4–dependent programmed cell death.
Thomas B. Thornley, Zemin Fang, Savithri Balasubramanian, Rafael A. Larocca, Weihua Gong, Shipra Gupta, Eva Csizmadia, Nicolas Degauque, Beom Seok Kim, Maria Koulmanda, Vijay K. Kuchroo, Terry B. Strom
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