Macrophage colony-stimulating factor enhances phagocytosis and oxidative burst of mononuclear phagocytes against Penicillium marneffei conidia

The responses of rabbit pulmonary alveolar macrophages (PAMs) and elutriated human monocytes (EHMs) to Penicillium marneffei, an emerging dimorphic fungus that may cause fatal disease in human immunodeficiency virus-infected patients, were studied. PAMs and EHMs comparably phagocytosed conidia of two P. marneffei strains in the presence of serum. Electron microscopy showed intraphagosomal destruction of conidia after 12 h. Serum-opsonized conidia elicited significantly more superoxide anion (O₂^-) release from EHMs compared to non-opsonized conidia, but equivalent O₂^- amounts to that elicited by serum-opsonized Aspergillus fumigatus conidia. Macrophage colony-stimulating factor (M-CSF) significantly enhanced phagocytosis of P. marneffei conidia by PAMs and EHMs, as shown by light microscopy. Moreover, M-CSF enhanced O₂^- production by EHMs in response to both serum-opsonized (P<0.001) and non-opsonized (P=0.03) conidia of A. fumigatus as well as conidia of the P. marneffei isolates (P<0.001 and 0.03). We conclude that M-CSF enhances phagocytosis and oxidative metabolism of mononuclear phagocytes suggesting a potential role for this cytokine in host defense against pulmonary and disseminated P. marneffei infection.