Effects of acemannan on macrophages

Abstract

Acemannan is a O-(I,4)-linked acetylated mannan. It is the major constituent of the pulp of the aloe vera plant (Aloe vera L.). It has several important therapeutic properties including acceleration of wound healing, inhibition of inflammation, immune stimulation, anticancer, and antiviral effects. It is unclear how acemannan exerts this wide variety of effects. One common cell, however, that appears to link all the biological effects of acemannan is the macrophage. Macrophages play a wide variety of roles and it is clear that activation of macrophages could play a role in the effects described above. For this reason, studies were undertaken to investigate the effects of acemannan on macrophages in vitro. A macrophage cell line, RAW 264.7 was exposed to acemannan in the presence or absence of suboptimal levels of interferon-y (IFN-y). It was found that acemannan alone was unable to exert any significant phenotypic change on macrophage morphology, surface molecule expression and function. However, in the presence of suboptimal concentrations of IFN-Y, acemannan caused highly significant activation over that induced by IFN-Y alone. The activation was expressed by increased macrophage size, cytoplasmic spreading and increased nitric oxide production. The biochemical and functional changes were expressed by increased surface adhesion molecule expression and surface Protein changes. These studies confirm that acemannan is a potent macrophage activating agent, but only in association with a second signal such as provided by interferon-y.