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Effects of skin-resident regulatory T cells on wound healing after burn injury

Xin, YW;Dong, N;Yao, WU;Chai, YF;

Objective To investigate the effect of skin-resident regulatory T cells (Tregs) on wound healing after burn injury. Methods 60 Foxp3DTR mice and 60 wild-type C57BL/6 mice were included in the present study. The Foxp3DTRdiphtheria toxin (DT) injection group (F-DT group) and the wild-type DT injection group (C-DT group) were further divided
into early (n=9) and late (n=9) groups according to the random number table method. In the early group, mice were injected
intraperitoneally with DT during the early stage (–1, 0 and 3rd days ofter injury) after burns, while in the late group, mice were injected at the late stage (5th, 7th and 9th days after injury). We took photos of mouse wounds at different time points, and measured the wound area to assess wound healing rate. After HE staining, re-epithelialization of the wound was observed under light microscope. In addition, flow cytometry was used to analyze changes in local infiltration and functional expression of Tregs in skin of wild-type mice at different time points after burns. Results Compared with the C-DT group, the rate of burn wound healing in the F-DT early group was significantly reduced (P<0.05), while the burn wound healing rate of the F-DT late group showed no significant difference compared with the C-DT group (P>0.05). In comparison to the C-DT group, HE staining in the F-DT early group revealed slower wound closure process and slower scar formation and crusting process, together with faster granulation tissue formation and obvious slower angiogenesis and re-epithelialization. Using flow cytometry to analyzing the infiltration of skin Tregs, CD4+ Foxp3+ T cells were significantly increased after burns, and gradually returned to basal level after reaching peak on day 5 (P<0.05). While CD25+ Treg cells were markedly decreased to baselines after peaking on day 3 (P<0.05). In addition, CTLA-4 expressions of skin Tregs was significantly enhanced after burns, and peaked on day 3 after burns, then gradually decreased to baseline values (P<0.05), while ICOS reached peak on day 5 postburn, and gradually decreased to normal range on day 11 (P<0.05). Conclusion The skin Tregs appear to be infiltrated into the wounds during the early stage after injury, which might contributes to promoting wound healing following burns.