Interaction between macrophage and parasite cells in lobomycosis. The thickened cell wall of Paracoccidioides loboi exhibits apertures to the extracellular milieu.

Lesioned, cutaneous, tissue fragments from five indians of the Caiabi tribe with lobomycosis, living in the Xingu National Park (Central Brazil), are analyzed by light and electron microscopy. Clusters of macrophages filled with parasite and/or cell wall debris, separated by collagen fiber bundles, characterize the morphological pattern seen in thick and thin sections. Paracoccidioides loboi within the phagocytic cells are multinucleate organisms whose cytoplasm contains mitochondria with few cristae, ribosomes and vacuoles; a large, dense, globular body and peculiarly curved mitochondrial profiles are described. From the outer portion of the double layered parasite cell wall, radial projections commonly emerge, rendering the structure conspicuously thicker and more irregularly surfaced than that seen in many other phagocytized yeast cell species. The cell wall layers from fungi possessing distinct subcellular organization show a weak or no reaction for acid phosphatase. Most of the foamy cells commonly seen by light microscopy are macrophages filled with fungal cell wall remnants which exhibit marked acid phosphatase activity. Occasionally, microchannels extending from the outer layer of the parasite cell wall to the macrophage surface and exocytic-like openings, possibly derived from the fusion of the macrophage membrane covering the parasite cell wall and the macrophage plasmalemma can be seen. Through such routes, material of texture and density similar to that of the outermost cell wall layer appears to be deposited extracellularly.