ObjectiveTo investigate the effects of Astragali Radix polysaccharides （APS） on the polarization of BV2 microglial cells in an oxygen-glucose deprivation/reoxygenation （OGD/R） model through regulation of the Toll-like receptor 4 （TLR4）/nuclear factor-κB （NF-κB） signaling pathway. MethodsThe OGD/R injury model of BV2 microglia was established and divided into blank group， OGD/R group and APS group （0.4 g·L^-1 APS）. Neuroinflammatory injury was induced by lipopolysaccharide （LPS） and treated with APS. The cells were divided into blank group， LPS group （1 mg·L^-1 LPS） and APS group （0.4 g·L^-1 APS+1 mg·L^-1 LPS）. Cell viability was detected using the cell counting kit-8 （CCK-8） assay. Cell morphology was observed under an inverted microscope. Nitric oxide （NO） content in the cell supernatant was determined by the Griess assay. The secretion levels of tumor necrosis factor-α （TNF-α）， interleukin （IL）-6， IL-10， and IL-4 were measured by enzyme-linked immunosorbent assay （ELISA）. Immunofluorescence （IF） was used to detect the double-positive rates of ionized calcium-binding adapter molecule-1/inducible nitric oxide synthase （Iba-1⁺/iNOS⁺） and ionized calcium-binding adapter molecule-1/arginase 1 （Iba-1⁺/Arg1⁺）， as well as the nuclear translocation rate of nuclear factor-κB p65 （NF-κB p65）. Protein expression levels of Iba-1， iNOS， Arg1， TLR4， and NF-κB p65 were detected by Western blot. ResultsIn the OGD/R injury model， compared with the blank control group， BV2 microglial cells in the OGD/R group were activated and exhibited amoeboid morphological changes. The secretion levels of NO， TNF-α， and IL-6 were significantly increased （P<0.01）. The double-positive expression rate of Iba-1⁺/iNOS⁺ and the protein expression of Iba-1 and iNOS were significantly increased （P<0.01）. The nuclear translocation rate of NF-κB p65 and the protein expression levels of TLR4 and NF-κB p65 were significantly increased （P<0.01）. The levels of IL-10 and IL-4 were significantly decreased （P<0.01）， and the double-positive expression rate of Iba-1⁺/Arg1⁺ and Arg1 protein expression were significantly decreased （P<0.01）. Compared with the OGD/R group， the APS group （0.4 g·L^-1） showed reduced cell activation， significantly decreased secretion levels of NO， TNF-α， and IL-6 （P<0.01）， significantly decreased double-positive expression rate of Iba-1⁺/iNOS⁺ and relative protein expression of Iba-1 and iNOS （P<0.01）， significantly decreased nuclear translocation rate of NF-κB p65 and protein expression levels of TLR4 and NF-κB p65 （P<0.01）， significantly increased levels of IL-10 and IL-4 （P<0.01）， and significantly increased double-positive expression rate of Iba-1⁺/Arg1⁺ and Arg1 protein expression （P<0.01）. In the LPS-induced neuroinflammation model， compared with the blank control group， the LPS group showed increased cell activation， significantly increased levels of NO， TNF-α， and IL-6， significantly increased Iba-1⁺/iNOS⁺ double-positive expression rate， NF-κB p65 nuclear translocation rate， and protein expression levels of Iba-1， iNOS， TLR4， and NF-κB p65 （P<0.01）， while IL-10 and IL-4 levels， Iba-1⁺/Arg1⁺ double-positive expression rate， and Arg1 protein expression were significantly decreased （P<0.01）. Compared with the LPS group， the APS group showed reduced cell activation， significantly decreased levels of NO， TNF-α， and IL-6， Iba-1⁺/iNOS⁺ double-positive expression rate， NF-κB p65 nuclear translocation rate， and protein expression levels of Iba-1， iNOS， TLR4， and NF-κB p65 （P<0.01）， while IL-10 and IL-4 levels， Iba-1⁺/Arg1⁺ double-positive expression rate， and Arg1 protein expression were significantly increased （P<0.01）. ConclusionAPS may reduce microglial activation and promote their polarization toward the M2 phenotype by inhibiting activation of the TLR4/NF-κB signaling pathway， thereby alleviating the neuroinflammatory response induced by OGD/R.