Macrophage colony-stimulating factor enhances the respiratory burst of human monocytes in response to Entamoeba histolytica.

Mononuclear phagocytes (MP) are probably the most capable effector cells of the body in the defense against virulent strains of E. histolytica. Killing of E. histolytica by MP appears to involve both oxidative and non-oxidative mechanisms. Thus, in this study we have investigated whether trophozoites of an axenic virulent strain E. histolytica HM1:IMSS (EH) were capable of eliciting an oxidative response in pure populations of freshly isolated human monocytes. Using a luminol-enhanced chemiluminescence assay we demonstrate that these cells produce a strong respiratory burst when challenged with live amebas over a wide range of MP:EH ratios. Furthermore, pre-incubation of monocytes with recombinant Macrophage Colony Stimulating Factor (M-CSF) could further increase the oxidative metabolism of MP in response to E. histolytica. Our results indicate that, in contrast to what occurs with polymorphonuclear leukocytes, the interaction of E. histolytica with MP leads to the production of reactive oxygen intermediates by this cells. The enhancement of this potent microbicidal mechanism by inflammatory cytokines may further increase the amebicidal capacity of human mononuclear phagocytes.