Reduced inflammatory response to Aeromonas salmonicida infection in common carp (Cyprinus carpio L.) fed with β-glucan supplements

The objective of the present study was to determine the action of beta-glucans as feed additives on the gene expression profile of some inflammatory-related cytokines from common carp (Cyprinus carpio L) during the early stages of a non-lethal bacterial infection with Aeromonas salmonicida. beta-glucan (MacroGard (R)), was administered daily to carp (6 mg per kg body weight) in the form of supplemented commercial food pellets for 14 days prior to infection. Control and treated fish were then intraperitoneally injected with PBS or 4 x 10(8) bacteria per fish and were sampled at time 0 and 6 h, 12 h, I day, 3 days and 5 days post-injection. Head kidney and gut were collected and the gene expression patterns for tnf alpha 1, tnf alpha 2, il1 beta, il6 and il10 were analyzed by quantitative PCR. Results obtained showed that treatment with beta-glucans generally down-regulated the expression of all measured genes when compared to their corresponding controls. After injection, highest changes in the gene expression levels were obtained at 6 h: particularly, in head kidney there was higher up-regulation of tnfa1 and tnfa2 in infected fish fed beta-glucans in comparison to control feed: however, in gut there was a significant down-regulation of tnf alpha 1, tnf alpha 2, il1 beta and il6 in infected fish fed beta-glucans. Analysis of carp specific antibodies against A. salmonicida 30 days after injection revealed their levels were reduced in the infected beta-glucan group. In conclusion, a diet supplemented with beta-glucan (MacroGard (R)) reduced the gene expression levels of some inflammation-related cytokines in common carp. Such a response appears to be dependent of organ studied and therefore the immunostimulant may be preventing an acute and potential dangerous response in gut, whilst enhancing the inflammatory response in head kidney when exposed to A. salmonicida. (C) 2012 Elsevier Ltd. All rights reserved.