Proinflammatory cytokine and cytokine receptor gene expression kinetics following challenge with Flavobacterium psychrophilum in resistant and susceptible lines of rainbow trout (Oncorhynchus mykiss)

Authors: KUTYREV, IVAN - Russian Academy Of Sciences; Cleveland, Beth; Leeds, Timothy - Tim; Wiens, Gregory - Greg

Submitted to: Fish and Shellfish Immunology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/26/2016
Publication Date: 10/12/2016
Citation: Kutyrev, I., Cleveland, B.M., Leeds, T.D., Wiens, G.D. 2016. Proinflammatory cytokine and cytokine receptor gene expression kinetics following challenge with Flavobacterium psychrophilum in resistant and susceptible lines of rainbow trout (Oncorhynchus mykiss). Fish and Shellfish Immunology. 58:542-553. doi: 10.1016/j.fsi.2016.09.053.

Interpretive Summary: The bacterium Flavobacterium psychrophilum causes bacterial cold water disease, and results in appreciable losses of farmed rainbow trout. In response to this problem, our center initiated a selective breeding program that, over five generations of breeding, increased rainbow trout resistance to this pathogen. The mechanism of increased resistance is not clear. In this study, we examined the expression, in spleen tissue, of twenty different immune genes that contribute to the inflammatory response. We found that fifteen genes were altered in expression following challenge. The expression of two genes differed between genetic lines and thus may contribute to the survival difference between the two lines. Further experiments are needed to confirm the role of these genes. This study is important because it characterizes the rainbow trout response to infection and demonstrates quantifiable differences between selectively bred fish lines.

Technical Abstract: Flavobacterium psychrophilum (Fp) is the causative agent of bacterial cold water disease (BCWD) which causes appreciable economic losses in rainbow trout aquaculture. We previously reported development of a genetic line, designated ARS-Fp-R that exhibits higher survival relative to a susceptible line, designated ARS-Fp-S, following either laboratory or natural on-farm challenge. The objectives of this study were to determine the temporal kinetics of gene expression between experimentally-challenged ARS-Fp-R and ARS-Fp-S fish and the correlation between gene expression and pathogen load. We developed a GeXP multiplex RT-PCR assay to simultaneously examine expression of immune-relevant genes, concentrating on tumor necrosis factor and interleukin-1 ligand/receptor systems and acute phase response genes. Spleen tissue was sampled at 6h, 24h, 48h and 144h post-challenge and pathogen load quantified by qPCR. Transcript abundance of cytokine genes tnfa1, tnfa2, tnfa3, il1b1, il1b2, il11a; acute phase response genes saa and drtp1; and putative cytokine receptors il1r1-like-b, il1r2, tnfrsf1a, tnfrsf9, tnfrsf1a-like-b increased following challenge while the transcript abundance of il1r-like-1 and tnfrsf1a-like-a decreased compared to PBS-injected line-matched control fish. Principal component analysis identified transcript levels of genes il1r-like-1 and tnfrsf1a-like-a as exhibiting differential expression between genetic lines. In summary, Fp i.p. injection challenge elicited a proinflammatory cytokine gene expression response in the spleen, with ARS-Fp-R line fish exhibiting modestly higher basal expression levels of several putative cytokine receptors. This study furthers the understanding of the immune response following Fp challenge and differences in gene expression associated with selective breeding for disease resistance.