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Research Project: Pathogen Characterization, Host Immune Response and Development of Strategies to Reduce Losses to Disease in Aquaculture

Location: Aquatic Animal Health Research

Title: Molecular immune response of channel catfish immunized with live theronts of Ichthyophthirius multifiliis

Author
item Xu, Dehai
item Zhang, Qi-zhong - Jiangnan University
item Shoemaker, Craig
item Zhang, Dunhua
item Moreira, Gabriel - Universidad De Sao Paulo

Submitted to: Fish and Shellfish Immunology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/30/2016
Publication Date: 4/11/2016
Citation: Xu, D., Zhang, Q., Shoemaker, C.A., Zhang, D., Moreira, G.S. 2016. Molecular immune response of channel catfish immunized with live theronts of Ichthyophthirius multifiliis. Fish and Shellfish Immunology. 54:86-92.

Interpretive Summary: In 2008, it was estimated that 42% of US channel catfish producers lost around 2000 pounds of catfish per producer per year due to the parasite Ichthyophthirius multifiliis in 2002. Catfish surviving natural Ich infections and/or immunized with live Ich theronts (infective stage of Ich) develop strong immune responses. Little is known about which immune genes are induced, how they interact and ultimately result in specific immunity against the parasite. This study evaluated the differential expression of 16 immune-related genes in channel catfish at different time points after immunization with I. multifiliis. The immunized fish showed much higher anti-Ich antibody than those of control fish. The anti-Ich antibody can immobilize the parasite and reduced Ich infection. Most immunized fish (95%) survived the Ich challenge. Expression of immunoglobulin genes exhibited a rapid increase from hour 4 to day 2 post immunization. Immune cell receptor genes showed up-regulation from hour 4 to day 6 post immunization, indicating an active involvement in cellular immune response. Gene expression of cytokine, complement factor and toll-like receptor exhibited a rapid increase from hour 4 to day 2 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 reinfection by Ich. Results of this study may allow for development of alternative control strategies for Ich by leading to a better understanding of the immune response of catfish to this parasite.

Technical Abstract: The parasite Ichthyophthirius multifiliis (Ich) has been reported in various freshwater fishes worldwide and results in severe losses to both food and aquarium fish production. The fish surviving natural infections or immunized with live theronts develop strong specific and non-specific immune responses. Little is known about how these 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 immunization with live theronts of I. multifiliis. The immunized fish showed significantly higher anti-Ich antibody expressed as immobilization titer and ELISA titer than those of control fish. The vast majority of immunized fish (95%) survived theront challenge. Expression of IgM and IgD heavy chain genes exhibited a rapid increase from 4 hours (h4) to 2 days (d2) post immunization. Expression of immune cell receptor genes (CD4, CD8, MHC I, MHC II, TcR-a, and TcR-ß) showed up-regulation from h4 to d6 post immunization, indicating an active involvement in cellular immune response. Cytokine gene expression (IL-1ßa, IL-1ßb, IFN-y and TNF-a) 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 infection by I. multifiliis.