OBJECTIVE To investigate the regulatory effect of vitamin D3(VD3)-mediated TIPE2 on macrophage function and phenotype in chronic rhinosinusitis with nasal polyps(CRSwNP).METHODS Peripheral blood samples were collected from 100 CRSwNP patients and 100 patients with simple nasal septum deviation.RT-qPCR and Western blot were used to measure the expression of TIPE2 and Arg-1,and chemiluminescence was used to measure VD3 concentration.In the J774A.1 macrophage cell line,TIPE2 was silenced,and in CRSwNP model mice,TIPE2 was overexpressed,followed by treatment with overexpressed TIPE2 combined with VD3.Western blot was used to measure the expression of TIPE2 and Arg-1,and ELISA was used to measure the expression of IL-4 and IL-13.RESULTS In the CRSwNP group,VD3 levels decreased,while TIPE2 and Arg-1 levels increased(all P<0.05).Arg-1 and TIPE2 were positively correlated(r2=0.994,P<0.05),and both were negatively correlated with VD3 levels(r2=0.652,P<0.05;r2=0.745,P<0.05).Silencing TIPE2 in J774A.1 cells led to a decrease in Arg-1,IL-4,and IL-13 levels(all P<0.05).In CRSwNP mice,overexpression of TIPE2 resulted in decreased VD3 and increased Arg-1,IL-4,and IL-13 levels,which were reversed by VD3 treatment(all P<0.05).CONCLUSION VD3 inhibits the expression of Arg-1,IL-4,and IL-13 in CRSwNP by downregulating TIPE2 expression.