Epithelial cells

Epithelioid cells are particularly activated and differentiated forms of exudate macrophages. They often lie in groups and with their broad eosinophilic cytoplasm are reminiscent of large epithelial cells. The enlarged, often centrally waisted nuclei are conspicuous.

Epithelioid cells are formed after macrophages have completely digested a phagocytosed product, e.g. bacteria, or have excreted an indigestible phagocytosed product by exocytosis. Epithelioid cells may also occur in delayed-type allergy if the defensive reaction is predominant(tuberculosis cutis luposa).

Epithelioid cells have a kind of barrier function and are at the same time maximally cytolytically activated by their massive production of NO, oxygen radicals and their secretion.