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In vitro effects of beta-hydroxy-beta-methylbutyrate (HMB) on cell-mediated immunity in fish.

beta-Hydroxy-beta-methyl butyrate(HMB) has been shown to counteract many of the negative effects of intensive animal production methods and results in increased growth and protection against diseases. In the present study, the effect of HMB on the immunocompetence cell activity in rainbow trout (Oncorhynchus mykiss) and carp (Cyprinus carpio) was examined. Pronephric phagocytes and lymphocytes were isolated from the fish and grown in culture medium (RPMI-1640) containing either 0, 0.1, 1, 5, 10, 25, 50 or 100 microg HMB/ml of medium. The effects of HMB on the respiratory burst activity (RBA) stimulated by phorbol myristate acetate (PMA), the potential killing activity (PKA) and lymphocyte proliferation stimulated by either concanavalin A (Con-A) or lipopolysaccharide (LPS) were examined. The addition of HMB to the culture medium increased the RBA by up to 84% (p<0.01) over that of cells grown without HMB. Similarly, the PKA of the phagocytes was also increased with HMB addition to the medium by up to 140% (p<0.01) over that of cells grown without HMB. Lymphocyte proliferation stimulated by both ConA and LPS was also increased approximately two-fold (p<0.01) when HMB was added to the culture medium at concentrations between 10 and 100 microg HMB/ml in both rainbow trout and carp. The greatest effects of HMB on RBA and PKA activities were observed at a concentration >50 microg HMB/ml while lymphocyte proliferation was maximally stimulated at 25 microg HMB/ml. In conclusion, the current study shows that HMB could potentially improve immunocompetence cell activity in fish through increased cell proliferation and functionality.