A recombinant sPLA2 protein promotes gut mucosal barrier against bacterial infection in fish

Secreted phospholipase A2 family protein (sPLA2) is associated with immune response and plays a critical role in the regulation of gut homeostasis. However, whether sPLA2 is involved in innate immunity in teleost is essentially unknown. For this purpose, we reported the identification of a classical sPLA2 in grass carp (CisPLA2) and elucidated its role in the antibacterial immunity in this study. The result of bioinformatics analysis showed that mammalian sPLA2-IIA is the most similar homologue to CisPLA2. CisPLA2 is expressed in a variety of tissues, including liver and gut, and is significantly upregulated in response to Aeromonas hydrophila infection. Recombinant CisPLA2 protein (rCisPLA2) showed significant antibacterial activity against A. hydrophila by enhancing the phagocytosis of host phagocytes in vitro. Moreover, rCisPLA2 induces significant expression of the antimicrobial molecules and tight junctions in the gut during bacterial infection. Fish administered with rCisPLA2 significantly alleviates the gut permeability and apoptosis. In addition, rCisPLA2 preserves the morphology of the gut mucosa and limits the colonization of A. hydrophila in systemic immune organs. These results indicate that CisPLA2 plays a crucial role in the regulation of gut mucosal barrier, and thus has a potential application for antimicrobial immunity in fish.