Modulation of cytokine expression by dietary levan in the pathogen aggravated rohu, Labeo rohita fingerlings

A novel prebiotic, levan, has shown a positive beneficial role as a dietary immune-nutrient in fishes. However, the research investigations on the underlying mechanism of immune protection is unavailable, therefore in the present study we have attempted to reveal the effects of dietary microbial levan on the expression of cytokine genes in the pathogen challenged Labeo rohita fingerlings. Fish were randomly distributed in two treatment group in triplicates, control group fed without levan and treated group fed with 1.25% (w/w%) of microbial levan in the diet. After 60 days of feeding trial, fish from each group were challenged with virulent A. hydrophila strain and tissue samples were collected on different time points, 3 h, 6 h, 12 h, 24 h, 48 h, and 96 h. Dietary administration of microbial levan, significantly upregulated the m-RNA levels of pro-inflammatory cytokines like IL-1β, TNF-α and IL-12p40 in the intestine, gill, kidney and liver in a time dependent manner. An increase of 2.13-fold in the expression of IL-1β at 96 h post challenge in the kidney cells was detected, however at early time points (3 h & 6 h) expression of the same was down regulated. Upregulation of the TNF-α gene in the gill, liver and kidney at 6 h and in the intestine at 12 h was noticed. IL-12p40 m-RNA expressed highest upregulation of 3.65-fold at 3 h in the intestine and 2.0-fold at 12 h in the gill. IL-10 m-RNA expression of intestine in the infected L. rohita displayed 7.57-fold downregulation. Furthermore, increased respiratory burst activity and serum lysozyme activity was observed in a time dependent manner in infected rohu fed with levan supplementation. Overall, the current study revealed the upregulation of immune responsive cytokine genes (IL-1β, TNF-α and IL-12p40) with dietary microbial levan against the pathogen infected stress in Labeo rohita fingerlings and thus supports use of levan as food additive in aquaculture.