SMAD3 and pemphigus foliaceus: On the other hand, DPP4 deficiency significantly not only suppressed CG-induced protein expression of DPP4 but also downregulated the mesenchymal marker (i.e., type I collagen) and TGF-β/SMAD3 signaling axis (Fig. 5d, f), suggesting DPP4 deficiency alleviated CG-induced PF mainly via reversing EMT process mediated SMAD3 signaling pathway.