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

Effects of β-glucan administration on survival and immune modulations were studied in Cyprinus carpio against the bacterial pathogen, Aeromonas hydrophila. β-glucan was extracted from Saccharomyces cervisiae and purified. A virulent strain of the pathogen A. hydrophila was collected from infected fish. Different concentrations of β-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 μg 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 μg 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 mRNA 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 μg 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.