In vitro exposure with beta-hydroxy-beta-methylbutyrate enhances chicken macrophage growth and function

beta-Hydroxy-beta-methylbutyrate (HMB), a leucine catabolite, has been show n to decrease broiler mortality. One possible target of HMB action may be t he cells of the immune system. Macrophages from a chicken macrophage cell l ine, MQ-NCSU, were exposed to 0, 10, 20, 40, 80, and 100 mu g of HMB per 5 x 10(4) cells in a 96-well culture plate. After 24 h of exposure, macrophag e proliferation was quantitated by an MTT bioassay. In duplicate experiment s, HMB stimulated growth over control (p less than or equal to 0.05) at a w ide range of doses. Macrophages were exposed to 20 and 80 mu g of HMB and t he culture supernatant fractions tested for the presence of nitrite. HMB ex posure (20 mu g) increased nitrite production by 44.1% over the controls (E xperiment 1, p less than or equal to 0.035). To determine the phagocytic po tential of macrophages after HMB exposure, MQ-NCSU cell line and Sephadex-G 50(R)-elicited abdominal macrophages were incubated with fluorescent latex beads (1:40, macrophage to beads ratio) for 1 h and then analyzed by flow c ytometry. When exposed to 40 mu g HMB, the phagocytic potential of MQ-NCSU macrophages was significantly higher (31.7%) than that of the controls (p l ess than or equal to 0.0006). Sephadex-elicited macrophages exhibited 14.4% increased phagocytosis over controls when treated with 80 mu g HMB (p less than or equal to 0.0016). When MQ-NCSU macrophages were exposed to HMB, Fc -receptor expression was significantly elevated over the controls (p less t han or equal to 0.0001). These data demonstrate that HMB exposure induces p roliferation of macrophages in culture as well as enhances macrophage effec tor functions, such as nitrite production and phagocytosis. The findings of these studies imply that HMB can be used as a possible dietary immunomodul ator. (C) 1999 Elsevier Science B.V. All rights reserved.