Ultrastructural study of hepatic granulomas induced by Cryptococcus neoformans by quick-freezing and deep-etching method.

The ultrastructure of hepatic granulomas induced by Cryptococcus (C.) neoformans was studied by a quick-freezing and deep-etching (QF-DE) method. Viable yeast cells were inoculated intravenously into rats and the livers were prepared for QF-DE replicas. Two cytoskeletal components were identified in the cytoplasm of macrophages composing the cryptococcal granulomas. These were: intermediate filaments, mainly located in the perinuclear region, and actin filaments, which were extensively decorated with myosin subfragment 1 (S1) and formed networks in the peripheral portion of the cytoplasm. In addition, two types of macrophage pseudopodia were observed in the granulomas. These were cobble stone-like pseudopodia at the yeast-macrophages contract areas, and thin, long and occasionally interdigitating pseudopodia in which actin filaments were consistently observed. Dense networks of actin filaments were also seen in pseudopodia protruding into the tight structure of the capsule of C. neoformans. These results suggest a role for actin filaments as one of the main factors in the force generating system of the phagocytic process.