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Concept
Cellule épithelioïde
Résumé
According to a common point of view epithelioid cells (also called epithelioid histiocytes)
are derivatives of activated macrophages resembling epithelial cells.
Structurally, epithelioid cells (when examined by light microscopy after stained with hematoxylin and eosin), are elongated, with finely granular, pale eosinophilic (pink) cytoplasm, and central, ovoid nuclei (oval or elongate), which are less dense than that of a lymphocyte. They have indistinct shape and often appear to merge into one another, forming aggregates known as giant cells. When examined by transmission electron microscopy in epithelioid cells in the field of Golgi lamellar complex are taped not only zonated, but also sleek vesicles with dense center, and also great many (more than 100) large granulas with diameters up to 340 nm and with finegranular matrix more light than in macrophage granulas, sometimes with perigranular halo. “The most prominent feature of these cells is the enormous Golgi area; up to 6 individual stacks of Golgi cisternae may be present as well as a few bristle-coated and numerous smooth vesicles”. Epithelioid cells have tightly interdigitated cell membranes in zipper-like arrays that link adjacent cells. This cells are central in the formation of granulomas, which are associated with many serious diseases. In granulomas, epithelioid cells perform the functions of delimiting.
It is shown that the epithelioid cell cytoskeleton formed by filaments differs significantly from the macrophage cytoskeleton. A large increase in the number of filaments occurs in these cells, where filaments (90 to 100 A) surround the cytocentrum as a distinctive annular bundle often branching into the cytoplasm. Due to such cytoskeleton contiguous epithelioid cells display elaborate cytoplasmic interdigitation. By using the quick=freeze and freeze-substitution methods (prompt freezing, penetrating etching and freeze-substitution) it has been shown that the organizations three-dimensional metastructure cytoskeleton of the epithelioid cells, formed in the focus of granulomatous inflammation, more compatible to cytoskeleton characteristic of typical epithelial cell than to cytoskeleton of active and movable macrophages.
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