Opposite effects of human monocytes, macrophages, and polymorphonuclear neutrophils on replication of Blastomyces dermatitidis in vitro

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Abstract
The purpose of this study was to determine the effects of human monocytes, macrophages, and polymorphonuclear neutrophils (PMN) on the fungal pathogen Blastomyces dermatitidis in vitro. Peripheral blood monocyte monolayers significantly inhibited the replication of a virulent strain (V) and an avirulent strain (AV) of B. dermatitidis by 35 and 28%, respectively. Macrophage monolayers, derived from monocytes by in vitro culturing for 9 days, also inhibited the replication of V and AV in 24-h cocultures; in 72-h cocultures, the inhibition was increased (85 and 88%, respectively). By contrast, PMN stimulated the replication of V and AV in 24-h cocultures (i.e., 45%; AV, 18%) and in 72-h cocultures (V, 68%; AV, 65%). No effect was observed in 2-h cocultures of PMN and B. dermatitidis, even though Candida albicans was killed by PMN in concurrent experiments. PMN stimulated replication of V in a dose-dependent manner, and viability of PMN was not a requirement for the achievement of this effect. These results indicate that monocytes and macrophages significantly inhibited the replication of B. dermatitidis, whereas PMN had an opposite effect. Our findings raise the possibility that these phagocytic cells may have similar opposing effects on the replication of B. dermatitidis in vivo.