In order to investigate the regulatory effect of Codonopsis saponins on the immunosup-pression caused by H9N2 subtype avian influenza virus(AIV)infection,rat pulmonary microvas-cular endothelial cells(RPMECs)were incubated with different concentrations of Codonopsis sap-onins(5,10 and 20 mg/L).The expression level of PD-L1 was detected by RT-PCR and flow cy-tometry,and the contents of TNF-α,IFN-y and IL-10 in supernatant were detected by ELISA kit.The titer of H9N2 AIV in supernatant was detected by plaque method.Then,a co-culture system of RPMECs and T cells was established using a Transwell plate with an aperture of 8 μm to mimic the migration of circulating T cells across microvessels to the site of viral infection.RPMECs were cultured in the upper chamber of Transwell,inoculated with H9N2 AIV,supplemented with 20 mg/L Codonopsis saponins 1 h later,and T cells 36 h later.After 8 h of treatment,T cells in the lower compartment were collected and the proportions of CD4+T cells and CD8+T cells were detected by flow cytometry,the expression levels of IL-2,IFN-y and granzyme B in the superna-tant were detected by ELISA,and the proportions of perforin-1 positive T cells were detected by flow cytometry.The proliferation activity of T cells was detected with the MTT cell proliferation and cytotoxicity assay kit,and the percentage of apoptotic cells was detected by flow cytometry af-ter staining of T cells with Annexin V-FITC/PI.The experimental results showed that Codonopsis saponins could significantly reduce the expression level of PD-L1,IL-10 and TNF-α in RPMECs in-duced by H9N2 AIV infection,and reduce the apoptosis rate of T cells.However,the expression levels of IL-2,IFN-y,perforin-1 and granzyme B in transendothelial migration T cells and the pro-liferation activity of T cells were significantly increased.In this study,Codonopsis saponins can sig-nificantly inhibit the expression of H9N2 AIV-induced PD-L1 in RPMECs,enhance the antiviral function of T cells migrating across the endothelial layer,and enhance the resistance of host to H9N2 AIV.
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