Phagocytosis and intracellular killing of pathogenic yeasts by human monocytes and neutrophils.

The kinetics of phagocytosis and killing of four fungal forms with varying virulence by two types of phagocytic cells was examined. Human monocytes ingested Saccharomyces cerevisiae, Candida tropicalis, and the blastospores of Candida albicans more rapidly than did human neutrophils. There was no difference in the rate of phagocytosis of C. albicans pseudohyphae by these two cell types. Intracellular killing of each of the four fungal forms was consistently and significantly more rapid by monocytes than by neutrophils. Neutrophils were unable to destroy ingested C. albicans pseudohyphae. These experiments suggest that the monocyte plays an important role in host defenses against fungal diseases and that the relative virulence of the pathogenic yeasts in human disease may be related to the ability of these organisms to survival after being ingested by circulating phagocytes.