Inflammatory and stress biomarker response of Aeromonas hydrophila infected rohu, Labeo rohita fingerlings to dietary microbial levan

Abstract An experiment was conducted to study the effect of microbial levan supplemented diet on innate and adaptive immune responses as well as stress biomarkers of pathogen challenged Labeo rohita fingerlings. Fish were randomly divided into two groups in triplicates and fed with a pre-standardized dose of 1.25% (w/w%) levan and without levan (control group) for 60 days. Post completion of the feeding trial, fish from both treatment groups were challenged with a pathogenic strain of A. hydrophila and samples were collected on different time points till 96 h. The results of the study showed that supplementation of microbial levan significantly upregulated the mRNA levels of TLR22, β-2 M and IFN-γ, and downregulated TGF-β in the intestine, gill, kidney and liver in a time-dependent manner. Significant decrease in the expression of TGF-β in the hepatic cells was noticed at later time points of 24, 48 and 96 h post-challenge with the highest of 2.66 fold at 48 h. Upregulation of the β-2 M gene at 48 h and 96 h was noticed in the intestine, gill, liver and kidney. Maximum expression of IFN-γ was observed at highest time points of 96 h in both intestine and gill, whereas 3.4-fold in the liver at 6 h and 2.6-fold in the kidney at 24 h was noticed. TGF-β expression analysis displayed the significant downregulation with a maximum decrease of 2.6 fold in the gill at 12 h, while a 2.3-fold and 2.5-fold decrease were noticed at 48 h in the kidney and liver, respectively. Total immunoglobulin level and myeloperoxidase content of A. hydrophila infected rohu increased upto 24 h in the levan-fed group compared to the control. Remarkable decrease of stress biomarkers such as serum cortisol, blood glucose, and HSP70 in the liver, muscle and gill, was observed due to dietary feeding of levan at 24 h. In totality, the present study revealed the significant upregulation of immune responsive genes (TLR22, β-2 M and IFN-γ), downregulation of regulatory gene (TGF-β) and decrease of HSP70, cortisol and blood glucose with dietary microbial levan supplementaion in infected Labeo rohita fingerlings. These findings on the modulation of immune responsive gene and stress parameters provide an understanding about the molecular basis of the function of prospective prebiotic, microbial levan.