Objective To study if IRF1 could regulate the polarization by IRF 1 and M1 status and affect M1 media-ted antitumor function .Methods U937 derived M1 macrophage ( U937-M1 ) model was established .The cells were devided into 4 groups:the PMA pretreated unpolarized macrophage (M0), the PMA, IFN-γand LPS induced M1 macrophage (M1), the siRNA of IRF1 knocked down M1 macrophage (siIRF1) and the negative control siR-NA treated M1 macrophage (siC).Furthermore, the expression of CD86 and CD206 was detected by flow cytome-try, the M1/M2 associated markers (IL-12p35,IL-12p40,IL-23p19,IL-6,TNF-α/IL-10) and IFNB1 were ana-lyzed by qPCR,the expression of IL-12p70 and IL-10 was examined by ELISA, the expression of IRF1 and IRF5 was detected by Western blot , the proliferration and apoptosis of HCC were analyzed by CCK 8 and flow cytometry , respectively.Results Compared with the U937-M1, the IRF1 knocked down group showed impaired CD 86 expres-sion, but enhanced CD206 expreesion ( P<0.05 ); the expression of M1 related cytokines including IL-12p35, IL-12p40,IL-23p19,IL-6,TNF-αand IFNB1 was decreased, but M2 related cytokine IL-10 level was increased (P<0.01);the expression of IFN-β, IL-12p70 and IRF5 was impaired, but IL-10 was enhanced (P<0.05).In IRF1 knocked down U937-M1, the CCK8 analysis indicated that the M1 mediated anti-proliferation effects on hepatoma carcinoma cell were turned to pro-proliferation ( P<0.05);the flow cytometry showed that the M 1 mediated pro-ap-optosis effects were reversed to anti-apoptosis ( P<0.01 ) .Interestingly , IRF5 and IFN-βwere decreased at both mRNA and protein levels in IRF1 knocked down U937-M1 compared with the U937-M1 (P<0.01).Conclusions IRF1 may partly modulate IRF5 and IFN-β, and further regulate M1 polarization and its antitumor effects .