The related immunity responses of red swamp crayfish (Procambarus clarkii) following infection with Aeromonas veronii

Aeromonas veronii is a typically opportunistic pathogen of aquatic animals as well as human beings, and it was one of the main pathogenic factors for septicemia in aquatic animals. In our previous study, a virulent strain of A.veronii was isolated from naturally infected crayfish Procambarus clarkii, which could cause serious disease for healthy crayfish. In this study, to determine the immune response of P. clarkii to the isolated A. veronii, the histopathology, the total hemocyte count (THC), the activities of immune-related enzymes, and the expression profiles of immune-related genes were evaluated. The results showed that the hepatopancreas, intestine, and gills of crayfish exhibited obvious tissue damage after being infected with A.veronii. The THC was dramatically reduced in the hemolymph of crayfish after being infected with A.veronii, which suggested that the immune system of P. clarkii was seriously damaged. Compared to the control group, the activities of acid phosphatase (ACP), alkaline phosphatase (AKP), phenoloxidase (PO), and lysozyme (LYZ) in the hemocytes, hemolymph, and hepatopancreas, and gills were increased in the A. veronii-infected crayfish after some time points. Additionally, upon A.veronii infection, the mRNA expression levels of eight immune-related genes including hemocyanin, lysozyme, anti-lipopolysaccharide factor 3, peroxiredoxin 6, prophenoloxidase, C-type lectin, astacidin, and Rab7 showed significant changes, respectively, in hepatopancreas, intestine, and gills. Our data demonstrated that the A. veronii could trigger a comprehensive innate immune response in P. clarkii. Our results could provide a theoretical foundation for better understanding the non-specific immunity of P. clarkii to A.veronii infection