Ultrastructural Observations on Penicillium marneffei in Natural Human Infection

The ultrastructure of Penicillium marneffei and the host response to the infection were studied in two patients. One was immunocompetent and the other an immunosuppressed renal graft recipient. In the immunocompetent patient it was observed that all the yeast cells were phagocytosed and were found either within membrane-bound vacuoles or lying freely within the cytoplasm of the macrophages. It was postulated that continuous lysosomal fusion with the phagolysosomes and multiplication of the fungi within the phagocytic vacuoles might eventually lead to the rupture of the vacuoles with release of the organisms into the cytoplasm of the macrophages. In the second patient, the immunosuppressive effects of corticosteroids might account for the large number of nonphagocytosed fungi in the tissue space, and the failure to form large phagocytic vacuoles.