Administration of yeast glucan enhances survival and some non-specific and specific immune parameters in carp (Cyprinus carpio) infected with Aeromonas hydrophila

Effects of beta-glucan administration on survival and immune modulations were studied in Cyprinus carpio against the bacterial pathogen, Aeromonas hydrophila. beta-glucan was extracted from Saccharomyces cervisiae and purified. A virulent strain of the pathogen A. hydrophila was collected from infected fish. Different concentrations of beta-glucan were administered to test animals on day 1, 3 and 5 through different routes (intraperitoneal injection (ip), bathing and oral administration). Control and test animals were challenged by ip injection of LD50 concentration of A. hydrophila on day 7 and mortality was observed and Relative Percent Survival (RPS) was calculated. Intraperitoneal injection of 500 mu g of glucan significantly enhanced the RPS; bathing and oral administration of glucan did not influence the RPS. On day 7, test animals injected with 100, 500 and 1000 mu g of glucan had a significant increase in total blood leucocyte counts and an increase in the proportion of neutrophils and monocytes. Superoxide anion production by kidney macrophages was also elevated. RT-PCR and northern blot analysis of interleukin-1 m RNA showed elevated expression in kidney on day 7 in fish injected with glucan. Glucan had an adjuvant effect on antibody production as pretreatment by injection of 100-1000 mu g glucan/fish resulted in the highest antibody titer against A. hydrophila following vaccination. Classical and alternative complement pathways were not affected by glucan administration by any of the three routes. (c) 2005 Elsevier Ltd. All rights reserved.