Ultrastructural Heterogeneity of Epithelioid Cells in Cutaneous Organized Granulomas of Diverse Etiology

Abstract

In organized granulomatous inflammation, activated macrophages terminally differentiate into epithelioid cells (ECs). By light microscopy, individual ECs appear similar, irrespective of the inciting agent. Ultrastructural analysis of a number of clinical and experimental granulomas in man and mice reveals, however, three distinct varieties of these cells. They are classified as follows: (1) EC-I cells containing a mixture of lysosomal-dense bodies and phagolysosomes and arrays of rough endoplasmic reticulum in the cytoplasm; (2) EC-II cells showing primarily a secretory mode with prominent Golgi bodies and rich arrangement of dilated rough endoplasmic reticulum with no phagocytic vacuoles; and (3) EC-III cells containing large multisized vesicles crowded throughout the cytoplasm and presently of unknown function. Although the unique appearance of these cells offers little diagnostic help, the cells do distribute differentially in different granulomas. The EC-I cells tend to predominate in infectious granulomas and where an excess of foreign material and debris is present. The EC-II cells are most characteristic of active sarcoidal granulomas, and the EC-III cells appear in chronic, long-standing granulomas. The heterogeneic nature of these cells seems to suggest their functions in granulomatous inflammation are not always the same.

Electron Microscopic Observations of Epithelioid Cell Granulomas Experimentally Induced by Prototheca in the Skin of Mice

“…Assuming this staging to be valid, macrophageslepithelioid cells at various stages of differentiation may be seen at sites of epithelioid granulomatous inflammation. On the other hand, Epstein (10) considers that there are three distinct types of epithelioid cells, Ee-I, EC-II, and EC-III. EC-I cells are abundantly present in infectious granuloma, along with considerable foreign material, lysosomal bodies, and arrays of rER in the cytoplasm.…”