Encapsulation, vacuolation and phagocytosis of the opportunistic fungal pathogen Cryptococcus in the liver of an immunocompetent host.

The cellular characteristics of the opportunistic fungal pathogen Cryptococcus species were investigated in the infected liver of an immunocompetent host using transmission electron microscopy (TEM). With no records of immunodeficiency, the 3-year-old female patient displayed a high-grade fever, lethargy and increasing jaundice. TEM analysis revealed the presence of round yeast cells in the patient's liver. These fungal yeast cells exhibited an array of cellular events in the host's liver: (i) the formation of polysaccharide capsules outside the cell wall, (ii) vacuolation in the cytoplasm and (iii) phagocytosis by Kupffer cells. The yeast cells were surrounded by electron-transparent polysaccharide capsules (approximately 5 μm thick). A series of yeast vacuolations were observed at different stages of cell development. As vacuoles occupied the cytoplasm of yeast cells, the polysaccharide capsules were thinner and more electron-dense than those of intact yeast cells. Certain yeast cells were phagocytosed by Kupffer cells through the budding scars or discontinued regions in the cell walls. These observations suggested that the patient was suffering from liver cryptococcosis. This study provides insights into the behavior of opportunistic fungal pathogens in the livers of immunocompetent patients.