Objective:To explore the role of macrophage polarization on pericyte-to-myofibroblast transition and renal allograft fibrosis after kidney transplantation(KT).Methods:Allograft tissues were harvestedfrom recipients with chronic allograft dysfunction(CGD)and normal kidney tissues.The expression and distribution of M1/M2 macrophages in kidney tissues were detected by routine and immunofluorescent staining; mRNA of CD68, CD206 and iNOS detected by polymerase chain reaction(PCR); Murine vascular pericytes subjected to TGF-β1 in vitro and the expressions of α-SMA and PDGFR-β in perivascular cells detected by immunoblotting and cellular fluorescence; The co-culturing models of vascular pericytes and M1/M2 macrophages were constructed.The expressions of α-SMA and PDGFR-β in pericytes were detected by immunoblotting, cellular fluorescence and PCR.Results:A marked infiltration of CD68+ iNOS+ M1 macrophages was present in allograft tissues of recipients with CGD while no obvious infiltration of CD68 + CD206 + was observed.The mRNA levels of CD68, iNOS and CD206 were significantly higher in CGD group than those in control group( P<0.05); In CGD allograft tissues, protein expressions of α-SMA and PDGFR-β spiked markedly( P<0.05)while cells with double staining of α-SMA and PDGFR-β were markedly infiltrated in interstitial area of CGD allograft.TGF-β1 could induce a marked elevation of PMT-related markers in a time-dependent manner( P<0.05); Immunoblotting and cellukar fluorescence indicated that M1 macrophages could promote the elevations of α-SMA and PDGFR-β in pericytes in vitro while M2 macrophages showed no effect on pericyte-to-myofibroblast transition in pericytes. Conclusions:M1 macrophage polarization may promote the formation of renal allograft interstitial fibrosis through promoting PMT.