Expression of immune genes in systemic and mucosal immune tissues of channel catfish vaccinated with live theronts of Ichthyophthirius multifiliis

Authors: Xu, Dehai; MOREIRA, GABRIEL - Brazil University; Shoemaker, Craig; Zhang, Dunhua; Beck, Benjamin

Submitted to: Fish and Shellfish Immunology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/20/2017
Publication Date: 7/15/2017
Citation: Xu, D., Moreira, G.S., Shoemaker, C.A., Zhang, D., Beck, B.H. 2017. Expression of immune genes in systemic and mucosal immune tissues of channel catfish vaccinated with live theronts of Ichthyophthirius multifiliis. Fish and Shellfish Immunology. 66:540-547.

Interpretive Summary: This study evaluated the molecular immune responses in mucosal (gill, intestine) and systemic (spleen, liver) immune tissues of channel catfish vaccinated with live theronts (infectious life stage) of the parasite Ichthyophthirius multifiliis (Ich). Ich is a common and severe parasite in freshwater fish and leads to heavy economic losses (greater than $10 million annually) in both food and ornamental fish production. Chemical treatment of Ich costly and often not effective after the parasite penetrates into the fish host skin and gill tissue. There is an urgent need for better understanding of the nature of protective immunity in order to develop an effective vaccine against the parasite. Results of this study demonstrated significantly higher antibody levels and survival (95%) in vaccinated fish than non-vaccinated control fish. Expression of immunoglobulin heavy chain genes exhibited a rapid increase from 4 hours (h 4) to 2 days (d 2) post vaccination. Immune cell receptor genes were more highly upregulated and remained upregulated for longer duration in spleen/liver than in gill/intestine of the vaccinated fish. The cytokine genes were rapidly upregulated in tissues of vaccinated fish, with peak expression from h 4 to d 1 post vaccination. Results of this study revealed the molecular immune responses in tissues of vaccinated fish and demonstrated that Ich vaccination resulted in innate and adaptive immune responses against Ich infection. This study offers new insight into the molecular actors that may govern the protective efficacy of Ich vaccination against Ich infection.

Technical Abstract: Ichthyophthiriasis caused by Ichthyophthirius multifiliis (Ich) has a worldwide distribution and affects almost all species of freshwater fishes. Fish surviving natural infection and/or immunized with Ich develop strong innate and adaptive immune responses. However, there is a lack of the knowledge regarding immune gene expression patterns in systemic and mucosal immune tissues, and how immune genes interact and lead to innate and adaptive immune protection against Ich infection in fish. The objective of this study was to investigate the expression of innate and adaptive immune-related genes in systemic (liver, spleen) and mucosal (gill, intestine) tissues of channel catfish over time following vaccination with live Ich theronts. The vaccinated fish showed significantly higher antibody titers and survival (95%) than those of mock immunized fish. Expression of IgM and IgD heavy chain genes exhibited a rapid increase from 4 hours (h4) to 2 days (d2) post-vaccination in both systemic and mucosal immune tissues. Immune cell receptor genes (CD4, CD8-a, MHC I, MHC II ß, TcR-a, and TcR-ß) were more highly upregulated and remained upregulated for longer duration in systemic tissues than in mucosal tissues of the vaccinated fish. The cytokine genes IL-1ßa and IFN-gamma were rapidly upregulated in both systemic and mucosal tissues of vaccinated fish, with peak expression from h4 to d1 post-vaccination. Toll-like receptor genes TLR-1 and TLR-9 showed relatively stable upregulation in the gill of immunized fish following vaccination. Results of this study revealed the molecular immune responses in mucosal and systemic tissues of vaccinated fish and demonstrated that Ich vaccination resulted in innate and adaptive immune responses against Ich infection.