ObjectiveTo investigate the effect of HBsAg on the expression of interferon-α (IFN-α) in peripheral blood plasmacytoid dendritic cells (pDCs) induced by the stimulator of interferon genes (STING) signaling pathway activated by cyclic GMP-AMP (cGAMP). MethodPeripheral venous blood was collected from healthy adults and the patients with chronic hepatitis B virus (HBV) infection who attended the outpatient service or were hospitalized in Department of Infectious Diseases, The Affiliated Hospital of Xuzhou Medical University, from February to December 2016, and peripheral blood mononuclear cells (PBMCs) were isolated and extracted. After the STING agonist cGAMP was added to PBMCs, ELISA was used to measure the levels of IFN-α, interferon-β, and tumor necrosis factor-α in supernatant. PBMCs from healthy adults were pre-incubated with HBsAg and then stimulated by cGAMP, and supernatant was collected to measure IFN-α. The magnetic-activated cell sorting method was used to remove pDCs from PBMCs, and after culture with cGAMP, ELISA was used to measure the level of IFN-α in supernatant. PBMCs from healthy adults were stimulated by HBsAg and/or cGAMP, and then flow cytometry was used to measure the frequency of pDCs. The independent samples t-test was used for comparison of continuous data between two groups. ResultsPBMCs from the patients with chronic HBV infection stimulated by cGAMP in vitro had a significantly lower level of IFN-α than healthy controls (469.72±18.95 vs 599.90±84.06, t=4.868, P=0.001). PBMCs from healthy adults co-cultured with HBsAg and stimulated by cGAMP had a significantly lower level of IFN-α than those in the non-HBsAg group (448.5±52.0 vs 571.0±30.8, t=4.500, P=0.011). Compared with PBMCs containing pDCs, PBMCs without pDCs stimulated by cGAMP had a significant reduction in the level of IFN-α (164.50±40.73 vs 339.50±35.33, t=6.482, P=0.001). Compared with PBMCs from healthy adults stimulated by cGAMP, PBMCs pre-incubated with HBsAg and then stimulated by cGAMP had a significant reduction in the frequency of pDCs (0.12%±0.04% vs 0.24%±0.04%, t=5.176, P=0.014). ConclusionHBsAg can inhibit the expression of IFN-α induced by the STING pathway in pDCs activated by cGAMP.