An epithelioid cell is a type of activated macrophage that exhibits morphological characteristics reminiscent of epithelial cells. These cells are typically larger than resting macrophages, possess abundant eosinophilic (pink-staining) cytoplasm, and display a smooth, elongated, or polygonal shape with a centrally located, often oval nucleus lacking prominent nucleoli. The term “epithelioid” refers to this epithelial‑like appearance, although the cells retain their origin from the monocyte‑macrophage lineage.
Histological context
Epithelioid cells are most commonly observed within granulomas, which are organized aggregates of immune cells that arise in response to persistent antigens, infectious agents, or foreign materials. Within granulomas, epithelioid cells may fuse to form multinucleated giant cells (e.g., Langhans‑type or foreign‑body giant cells). Their presence is a hallmark of several granulomatous diseases, including:
- Tuberculosis and other mycobacterial infections
- Sarcoidosis
- Leprosy (especially the tuberculoid form)
- Certain fungal infections (e.g., histoplasmosis, coccidioidomycosis)
- Foreign‑body reactions
Functional aspects
Epithelioid cells are considered to be in an activated state, exhibiting enhanced secretion of cytokines, chemokines, and growth factors that modulate the local immune response and promote tissue remodeling. They possess reduced phagocytic activity compared with resting macrophages but are involved in antigen presentation and the orchestration of chronic inflammatory processes.
Diagnostic significance
In histopathology, the identification of epithelioid cells assists in distinguishing granulomatous inflammation from other types of inflammatory infiltrates. Staining characteristics include strong positivity with hematoxylin‑eosin (H&E) due to the eosinophilic cytoplasm; immunohistochemical markers such as CD68 and CD163 confirm their macrophage origin.
Related terminology
- Epithelioid histiocyte – synonymous with epithelioid cell, emphasizing its histiocytic (macrophage) nature.
- Granuloma – a structured collection of epithelioid cells, lymphocytes, and, frequently, multinucleated giant cells.
References
- Robbins and Cotran Pathologic Basis of Disease, 10th ed. (Elsevier, 2020).
- WHO Classification of Tumours of the Haematopoietic and Lymphoid Tissues, 5th ed. (IARC, 2022).
Note: The information presented reflects current consensus in medical pathology and histology literature.