Interactions between Histoplasma capsulatum and macrophages from normal and treated mice: comparison of the mycelial and yeast phases in alveolar and peritoneal macrophages.

Interactions between macrophages (alveolar and peritoneal) from normal, vaccinated (with heat-killed yeast cells), and Mycobacterium bovis BCG-treated mice and the mycelial and yeast phases of Histoplasma capsulatum were observed. Phagocytosis of microconidia, small hyphal fragments, and yeast cells occurred 4 to 6 h after the infection of macrophage cultures. Conversion to the yeast phase began at 6 to 7 h and was complete after a 72-h incubation at 37 degrees C. Macrophages surrounded and adhered to macroconidia and large hyphal elements. More macrophages (65 to 68%) from BCG-treated mice contained fungi at 24 h than did macrophages from normal or vaccinated mice. Although there was no increase in the number of fungi in macrophages from vaccinated mice, only the macrophages from BCG-treated mice contained fewer fungi after 48 h of infection with the mycelial phase of H. capsulatum. Fungal growth was not inhibited in any of the macrophage cultures when infected with the yeast phase. The macrophages infected with yeast cells were destroyed after 48 to 72 h in the culture. Only BCG-treated macrophages survived infection with the mycelial phase, whereas macrophages from normal and vaccinated mice were destroyed by the infection.