Immobilization antigens provide orange-spotted grouper (Epinephelus coioides) protection against Cryptocaryon irritans infection

Abstract

Vaccination is a way to prevent Cryptocaryon irritans outbreaks and immobilization antigens (I-antigens) are considered for vaccine development against the parasite.However, the information of C. irritans I-antigens is limit. In this study, we characterized three immobilization antigen genes (CI-IA1, CI-IA2, and CI-IA8) from C. irritans. All three I-antigens contain signal peptides, transmembrane domains, and a GPI anchor. Conserved antigenic epitope sites were found in the I-antigens sequences. After removing signal peptides and transmembrane domains, the codons of truncated I-antigens were optimized and expressed in Escherichia coli. The purified recombinant I-antigens were recognized by grouper anti-serum generated by surface exposure or intraperitoneal injection with theronts, indicating that the recombinant I-antigens have immunogenicity. After intraperitoneal injection with recombinant I-antigens, it was found that vaccination with CI-IA1, CI-IA2, and CI-IA8 generated higher immobilization titer and protected grouper against C. irritans infection. The parasite reduced the rate of Ci-IA1, CI-IA2, and CI-IA8 by 25.55%, 17.13%, and 21.05%, respectively. Higher specific IgM antibody titers were detected in serum and mucus from the vaccine group. The regulation of immune-related genes after the vaccination was determined and showed that the adaptive immune response was active during the immunization. These findings suggested that vaccination with recombinant Ci-IA1, CI-IA2, and CI-IA8 elicits protective immunity in grouper against C. irritans and those I-antigens may serve as a potential antigen for vaccine development.