A BCWD-resistant line of rainbow trout exhibits higher abundance of IgT+ B cells and heavy chain tau transcripts compared to a susceptible line following challenge with Flavobacterium psychrophilum

Authors: ZWOLLO, PATTY - College Of William & Mary; HENNESSEY, ERIN - College Of William & Mary; MOORE, CATHERINE - College Of William & Mary; MARANCIK, DAVID - St George'S University; Wiens, Gregory - Greg; EPP, LINDA - College Of William & Mary

Submitted to: Developmental and Comparative Immunology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/14/2017
Publication Date: 5/4/2017
Citation: Zwollo, P., Hennessey, E., Moore, C., Marancik, D.P., Wiens, G.D., Epp, L. 2017. A BCWD-resistant line of rainbow trout exhibits higher abundance of IgT+ B cells and heavy chain tau transcripts compared to a susceptible line following challenge with Flavobacterium psychrophilum. Developmental and Comparative Immunology. 74:190-199.

Interpretive Summary: Selective breeding for disease resistance offers new opportunities for improving fish welfare in aquaculture. However, the mechanisms governing resistance remain poorly understood. At our location, we have produced a line of rainbow trout that has increased resistance against Flavobacterium psychrophilum, the cause of bacterial cold water disease (BCWD). In this study, we reanalyzed the abundance of B lymphocytes secreting immunogloblulin tau (IgT) which is a type of antibody that is unique to fish. We found that the resistant line had a higher abundance of IgT B-cells in immune tissues, and that after challenge, this difference was maintained relative to a susceptible line. Furthermore, the number of IgT cells inversely correlated with bacterial counts. This study is important because it characterizes the trout antibody response, demonstrates quantifiable differences between fish lines, and suggests immune and physiologic mechanisms associated with improved survival produced through selective breeding.

Technical Abstract: Bacterial Cold Water Disease (BCWD) is a common, chronic disease in rainbow trout, and is caused by the gram-negative bacterium Flavobacterium psychrophilum (Fp). Through selective breeding, the National Center for Cool and Cold Water Aquaculture has generated a genetic line that is highly resistant to Fp challenge, designated ARS-Fp-R (or R-line), as well as a susceptible "control" line, ARS-Fp-S (S-line). In previous studies, resistance to Fp had been shown to correlate with naive animal spleen size, and further, naïve R-line trout had been shown to have a lower abundance of IgM+ and IgM++ cells (ISCs) compared to S-line fish. Here we wished to first determine whether the abundance of IgT+ and/or IgT++ cells differed between the two lines in naïve fish, and if so, how these patterns differed after in vivo challenge with Fp. Fp challenge was by intramuscular injection of live Fp and tissue collections on day 5, 6, and/or 28 post-challenge, in two independent challenge experiments. Flow cytometric and gene expression analyses revealed that naïve R-line fish had a higher abundance of IgT+ B cells in their anterior kidney, spleen, and blood, compared to S line fish. Further, that after Fp challenge, this difference was maintained between the two lines. Lastly, abundance of IgT+ B cells and expression of secHCtau expression correlated with lower Fp pathogen loads in challenged fish. In the anterior kidney, IgM+ B cell abundance correlated with increased Fp loads. Together, these results suggest that IgT+ B lineage cells may play protective roles in the humoral immune response to Fp.