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

Beta-hydroxy-beta-methylbutyrate (HMB), a leucine catabolite, has been shown to decrease broiler mortality. One possible target of HMB action may be the cells of the immune system. Macrophages from a chicken macrophage cell line, MQ-NCSU, were exposed to 0, 10, 20, 40, 80, and 100 microg of HMB per 5 x l0(4) cells in a 96-well culture plate. After 24 h of exposure, macrophage proliferation was quantitated by an MTT bioassay. In duplicate experiments, HMB stimulated growth over control (p < or = 0.05) at a wide range of doses. Macrophages were exposed to 20 and 80 microg of HMB and the culture supernatant fractions tested for the presence of nitrite. HMB exposure (20 microg) increased nitrite production by 44.1% over the controls (Experiment 1, p< or =0.035). To determine the phagocytic potential of macrophages after HMB exposure, MQ-NCSU cell line and Sephadex-G50-elicited abdominal macrophages were incubated with fluorescent latex beads (1:40, macrophage to beads ratio) for I h and then analyzed by flow cytometry. When exposed to 40 microg HMB, the phagocytic potential of MQ-NCSU macrophages was significantly higher (31.7%) than that of the controls (p < or = 0.0006). Sephadex-elicited macrophages exhibited 14.4% increased phagocytosis over controls when treated with 80 microg HMB (p < or = 0.0016). When MQ-NCSU macrophages were exposed to HMB, Fc-receptor expression was significantly elevated over the controls (p < or = 0.0001). These data demonstrate that HMB exposure induces proliferation of macrophages in culture as well as enhances macrophage effector functions, such as nitrite production and phagocytosis. The findings of these studies imply that HMB can be used as a possible dietary immunomodulator.