Abstract: Objective To investigate the effect of protein C activator (PCA) from Agkistrodon acutus venom (AAV) in modulating early adaptive immune response of septic rats. Methods Rat models of sepsis were established by intraperitoneal injection of lipopolysaccharide (LPS; 10 mg/kg) in 36 SD rats, which were divided into 6 groups (n=6) for sample collection at 4, 6, 8, 12, 16 and 24 h after LPS injection, with 6 rats injected with saline as the control group. Another 36 rats were divided into two groups, and 30 min after LPS injection, the rats were treated with SEW2871 (a sphingosine- 1- phosphate receptor 1 agonist; 0.5 mg/kg) or PCA group (0.1 mg/kg), and each group was divided into 3 groups (n=6) for sample collection at 6, 12 and 24 h after LPS injection. Plasma IL-4, S1P, IL-12 and IFN-γ levels of the rats were detected using ELISA, and the expressions of S1PR1 and CD103 in the mesenteric lymph nodes were detected with immunofluorescence assay. Results The plasma levels of S1P, IL-12, IL-4 and IFN-γ (P<0.05) and the expressions of S1PR1 and CD103 in the mesenteric lymph nodes (P<0.05) all increased significantly in the rats 24 h after LPS injection; IFN-γ/IL-4 ratio increased progressively within 6 h after LPS injection and then subsided gradually. Compared with those in the corresponding sepsis model subgroups, the levels of S1P, IL-12 and IFN-γ increased while IL- 4 level decreased significantly (P<0.05), and the expression of S1PR1 and CD103 were reduced significantly (P<0.05) in SEW2871-treated rats; both the plasma level of IL-4 and the expression of S1PR1 in the mesenteric lymph nodes increased significantly in PCA-treated rats (P<0.05). Conclusion PCA can regulate the balance of inflammation and immune response in the early stage of sepsis in rats possibly through the S1P-S1PR1 pathway.

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