SMAD3 and endometriosis: Taken together, these data suggest that through promoting a predominantly type 2 immunity in lesions, promoting the aggregation of Tregs, Th2 cells, and M2 macrophages but keeping a low-level of Th1 cell aggregation in endometriotic lesions and possibly activating the TGF-β1/Smad3 signaling pathway, the platelets promote lesional fibrogenesis in endometriosis.