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 (O ncorhynchus mykiss) and carp (Cyprinus carpio) was examined. Pronephric pha gocytes and lymphocytes were isolated from the fish and grown in culture me dium (RPMI-1640) containing either 0, 0.1, 1, 5, 10, 25, 50 or 100 mug HMB/ ml of medium. The effects of HMB on the respiratory burst activity (RBA) st imulated by phorbol myristate acetate (PMA), the potential killing activity (PKA) and lymphocyte proliferation stimulated by either concanavalin A (Co n-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 cell s grown without HMB. Lymphocyte proliferation stimulated by both ConA and L PS was also increased approximately two-fold (p < 0.01) when HMB was added to the culture medium at concentrations between 10 and 100 <mu>g HMB/ml in both rainbow trout and carp. The greatest effects of HMB on RBA and PKA act ivities were observed at a concentration >50 mug HMB/ml while lymphocyte pr oliferation was maximally stimulated at 25 mug HMB/ml. In conclusion, the c urrent study shows that HMB could potentially improve immunocompetence cell activity in fish through increased cell proliferation and functionality. ( C) 2000 Elsevier Science B.V. All rights reserved.