An epithelioid cell is a specialized cell type, distinct from typical immune cells. These cells undergo specific changes, adopting a unique appearance and function. Their presence often signals particular immune responses, indicating the body’s attempt to manage challenges.
Understanding Epithelioid Cells
Epithelioid cells originate from macrophages, which are phagocytic immune cells. When macrophages encounter persistent stimuli, such as microorganisms or foreign bodies, they transform into epithelioid cells. This transformation involves changes in their internal structure and shape, adapting them for a different immune role.
These modified cells develop an elongated, slipper-shaped or oval appearance with abundant pale cytoplasm and a vesicular nucleus. They often align closely, resembling epithelial cells, which gives them their “epithelioid” name. While their parent macrophages are highly phagocytic, epithelioid cells exhibit significantly reduced phagocytic activity. Their primary function shifts from engulfing to contributing to a more organized immune response.
The process of this cellular change is a response to chronic inflammation, where the immune system attempts to contain a substance it cannot easily eliminate. Cytokines, signaling molecules released during immune responses, play a part in prompting this macrophage differentiation. This cellular specialization allows for the formation of distinct structures that help manage persistent threats within tissues.
Their Role in Granulomas
Epithelioid cells are central to the formation of granulomas, which are organized collections of immune cells. These structures develop when the immune system attempts to wall off substances it cannot clear. Granulomas commonly consist of epithelioid cells, along with other immune cells like lymphocytes and sometimes multinucleated giant cells.
Within a granuloma, epithelioid cells align closely, forming a compact barrier around the inciting agent. Their close apposition and intercellular junctions contribute to the structural integrity of the granuloma. This arrangement helps to physically contain persistent pathogens or foreign materials, preventing their spread throughout the body.
The formation of a granuloma is a containment strategy, isolating the source of inflammation. Epithelioid cells play a specific part in this containment, forming the bulk of the cellular wall. While they have limited phagocytic activity, their collective organization is effective in sequestering substances that are resistant to degradation. This structural contribution is a defining feature of chronic inflammatory responses.
Diseases Linked to Epithelioid Cells
The presence of epithelioid cells, particularly within granulomas, is a characteristic pathological feature in several medical conditions. Tuberculosis, caused by Mycobacterium tuberculosis, is a classic example where epithelioid granulomas are consistently observed. The body’s immune response attempts to contain the bacteria within these organized structures.
Sarcoidosis, a systemic inflammatory disease, also presents with non-caseating granulomas rich in epithelioid cells. In this condition, the immune system forms granulomas in various organs, including the lungs, skin, and lymph nodes, though the exact trigger is not fully understood.
Crohn’s disease, an inflammatory bowel condition, frequently shows granulomas containing epithelioid cells in the affected digestive tract. These granulomas are often non-caseating. Certain fungal infections, such as histoplasmosis or coccidioidomycosis, can also induce granuloma formation with epithelioid cells. The presence of these cells provides diagnostic clues, indicating a granulomatous inflammatory process in response to various persistent stimuli.