Abstract: Objective to investigate the effects of quercetin with a special focus on their effect on macrophage polarization after SCI. Methods Adult C57 mice underwent T10 spinal cord clip compression injury，then were randomly divided into SCI group and quercetin group. 1-14 d after SCI received quercetin by intraperitoneal injection(one time/day) in quercetin group, and received same normal saline in the SCI group. 3 d, 7 d and 14 d after SCI, the lesion section of SCI group and Quercetin group stained by immunofluorescent: M1 Macrophages phenotype cell labeled with iNOS, and M2 Macrophages phenotype cell labeled with Arg1. The mRNA expression of inflammatory factors in lesion site was detected by RT-PCR. The motor function was evaluated by Basso mouse scale(BMS) after SCI. Results Compare with SCI group, the expression of arginase-1 (associated with M2 macrophage phenotype) significantly increased in quercetin group (P<0.05). On the contrary, the expression of inducible nitric oxide synthase-iNOS (M1 phenotype marker) was down-regulated as demonstrated using immunohistochemistry (P<0.05). Furthermore, the production of NOS2 and tumor necrosis factor alpha was significantly reduced whereas the levels of interleukin 10 and TGF-β were elevated in quercetin group (P<0.05). The time course of functional recovery revealed that gradual recovery was observed in the subacute phase in quercetin group, little improvement was observed in SCI group(P<0.05). Conclusions it is found that quercetin could promote the shift of M1 to M2 phenotype and ameliorate the inflammatory microenvironment. Furthermore, the roles of quercetin in immunity modulation may enhance neuroprotective effects and partially contribute to the locomotor functional recovery after SCI.

Key words: Keywords: Spinal cord injury, Macrophage Polarization, Quercetin, Inflammation