Immune responses of channel catfish against parasite Ichthyophthirius multifiliis following theront vaccination

Abstract

Abstract Ichthyophthirius multifiliis (Ich) is a severe fish parasite and results in heavy losses of freshwater fish. The fish surviving natural infections or vaccinated with live theronts develop strong immune responses. Little is known about how immune genes are induced or how they interact and lead to specific immunity against I. multifiliis in channel catfish Ictalurus punctatus. This study evaluated the differential expression of immune-related genes, including immunoglobulin, immune cell receptor, cytokine, complement factor and toll-like receptors in head kidney from channel catfish at different time points after vaccination with live theronts of I. multifiliis. The vaccinated fish showed significantly higher anti-Ich antibody than those of control fish. The vast majority of immunized fish (95%) survived the parasite challenge. Expression of IgM and IgD heavy chain genes exhibited a rapid increase from 4 hours (h4) to 2 days (d2) post vaccination. Expression of immune cell receptor genes (CD4, CD8-α, MHC I, MHC II β, TcR-α, and TcR-β) showed up-regulation from h4 to d6 post vaccination, indicating that different immune cells were actively involved in cellular immune response. Cytokine gene expression (IL-1βa, IL-1βb, IFN-□ and TNF-α) increased rapidly at h4 post immunization and were at an up-regulated level until d2 compared to the bovine serum albumin control. Expression of complement factor and toll-like receptor genes exhibited a rapid increase from h4 to d2 post immunization. Results of this study demonstrated differential expression of genes involved in the specific or non-specific immune response post immunization and that the vaccination against Ich resulted in protection against I. multifiliis infection.