During parasite infection, serine protease inhibitors secreted by parasites play important roles in suppressing host defenses. However, the mechanism of immune regulation is unclear. In this study, a serpin gene from Trichinella pseudospiralis , named Tp -Serpin, was cloned and expressed, in order to reveal its role in the regulation of the host immune response in T. pseudospiralis infection. The results showed that Tp -Serpin encodes a 43 kDa protein that was recognized by serum from T. pseudospiralis infected mice at 60 days post-infection (dpi). Tp -Serpin was found to be expressed at all developmental stages of T. pseudospiralis . Inhibitory activity analysis showed that recombinant Tp -Serpin (r Tp -Serpin) effectively inhibited the hydrolytic activity of porcine pancreatic elastase (elastase P), human neutrophil elastase (elastase H), and mouse mast cell protease-1, but showed little inhibitory for human neutrophil cathepsin G (cathepsin G). Furthermore, r Tp -Serpin induced polarization of macrophages toward the alternatively activated phenotype (M2) alone by activation of the signal transducer and activator of transcription 3 signaling pathway, and inhibited lipopolysaccharide-induced classically activation (M1) in vitro . These data preliminarily demonstrate that Tp -Serpin may play an important role in the immunoregulation of T. pseudospiralis infection by activating the M2-polarized signaling pathway.
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