Freeze-fracture features of epithelioid cells, multinucleated giant cells, and phagocytic macrophages

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Abstract
The freeze-fracture morphology of epithelioid cells, multinucleated giant cells (Langhans’ type), and phagocytic macrophages was investigated. The intensely folded and interdigitating surface membranes of epithelioid cells and multinucleated giant cells displayed no specialized areas of cell contact. The size of the intramembranous particles (IMP) and the fact that the area density of IMPs was higher in the cytoplasmic (P) faces than in the external (E) faces of the cell membranes agreed with observations in other eukaryotic cells. The area densities of the IMPs suggest lower transport rates of molecules across the cell membranes of granuloma cells than of certain epithelial cells. Small pits were detected in the surface membranes of the granuloma cells but an extrusion of granules was not observed. The cytoplasmic granules displayed very different sizes and shapes ranging from spherical to rod-shaped. The latter type of granules (probably primary lysosomes) dominated in multinucleated giant cells. The granule membranes were studded with IMPs whose area densities increased with the granule size. Multilamellar bodies with smooth (lipid) fracture faces were found only in phagocytic macrophages. The nuclear pores of the granuloma cells were distributed over the entire surfaces of the nuclei and displayed moderate clustering. The values of the area densities of the nuclear pores were in keeping with the values observed in mammalian and human epithelial or mesenchymal cells, indicating similar exchange rates of molecules between the nucleoplasm and the cytoplasm in these different cell types. In a single phagocytic macrophage the E-face of the inner membrane of the nuclear envelope displayed a network of fine filaments whose nature is at present unknown.