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Problem: T-cells are key players in fighting the coronavirus disease 2019 (COVID-19). The checkpoint molecule B7-H4, a member of the B7 family, can inhibit T-cell activation and proliferation by inhibiting NF-kb expression. We aimed to elucidate the immunological role of soluble B7-H4 (sB7-H4) and B7-H4 in pregnant women suffered from an acute Sars-Cov2 infection. Methods: Expression levels of sB7-H4 and cytokines were detected by enzyme linked immunosorbent assay. B7-H4 and cytokines mRNA expression was analyzed by qPCR, and B7-H4 and NF-κb (p65) protein levels were investigated by western blot and immunofluorescence staining in placenta chorionic villous and decidual basalis tissues of COVID-19 affected women and healthy controls. Results: Fibrinoid necrosis in the periphery of placental villi was increased in the COVID-19-affected patients. sB7-H4 protein in maternal and cord blood serum and IL-6/IL-10 were increased while leukocytes were decreased during SARS-CoV-2 infection. Serum sB7-H4 level was increased according to the severity of SARS-Cov-2 infection. Cytokines (IL-6, IL-18, IL-1β, TNF-α), B7-H4 mRNA and protein in the decidual basalis tissues of COVID-19-infected pregnant women were significantly increased compared to healthy controls. IL-18 and IL-1β were significantly increased in the placenta chorionic villous samples of COVID-19 affected patients, while NF-κb (p65) expression was decreased. Conclusions: The expression of the immunological marker sB7-H4 correlated with the severity of COVID-19 disease in pregnant women. sB7-H4 and B7-H4 can be used to monitor the progression of COVID-19 infection during pregnancy, and for evaluating of the maternal immune status.