Functional analysis of the proteases overexpressed during the invasive and parasitic stages of Cryptocaryon irritans and their potential as vaccine antigens

Abstract

In this study, we aimed to analyze the functions of highly expressed proteases at the theront (invasive stage) and trophont (parasitic stage) phases of Cryptocaryon irritans during the infection process using RNAi. We also analyzed the potential of these proteases as candidate antigens for vaccination against the parasite by infecting tiger pufferfish (Takifugu rubripes) with the recombinant proteases. Compared with the control group, RNAi against four proteases (including peptidases) genes reduced the number of parasites that infected and left the fish after complete development. The four recombinant proteases were then purified and evaluated as candidate vaccination antigens. The number of parasites recovered from fish immunized with the C. irritans recombinant proteins was lower than that recovered from control fish; this difference was statistically significant when a recombinant cysteine protease was used. These results suggest that the C. irritans proteases overexpressed at the theront and trophont stages are important for infection (including invasion, food uptake, digestion, and development) and can be targeted for the development of vaccines against cryptocaryoniasis.