Epithelioid cell
Encyclopedia
Epithelioid histiocytes are activated macrophages resembling epithelial cells
: elongated, with finely granular, pale eosinophilic (pink) cytoplasm and central, ovoid nucleus(oval or elongate), which is less dense than that of a lymphocyte
. They have indistinct shape contour, often appear to merge into one another and can form aggregates known as giant cells.
Granuloma formation is a strategy that has evolved to deal with those pathogens that have learned to evade the host immune system by various means like resisting phagocytosis and killing within the macrophages. Granulomas try to wall off these organisms and prevent their further growth and spread. Many old scourges of mankind like tuberculosis, leprosy and syphilis fall into this category of diseases. Granuloma formation is also the feature of many of our newer problems like fungal infections, sarcoidosis and Crohn's disease.
Epithelium
Epithelium is one of the four basic types of animal tissue, along with connective tissue, muscle tissue and nervous tissue. Epithelial tissues line the cavities and surfaces of structures throughout the body, and also form many glands. Functions of epithelial cells include secretion, selective...
: elongated, with finely granular, pale eosinophilic (pink) cytoplasm and central, ovoid nucleus(oval or elongate), which is less dense than that of a lymphocyte
Lymphocyte
A lymphocyte is a type of white blood cell in the vertebrate immune system.Under the microscope, lymphocytes can be divided into large lymphocytes and small lymphocytes. Large granular lymphocytes include natural killer cells...
. They have indistinct shape contour, often appear to merge into one another and can form aggregates known as giant cells.
Clinical significance
Epithelioid cells are an essential characteristic of granulomas: that is to say that without them a granuloma is not a granuloma. A Granuloma can be defined as "an organized collection of epithelioid macrophages." A non-purist would give a broader definition of the granuloma as "an organized collection of macrophages." The latter definition would include mere collections of giant cells surrounding inert substances like suture material – the so called "non-immune granulomas."Granuloma formation is a strategy that has evolved to deal with those pathogens that have learned to evade the host immune system by various means like resisting phagocytosis and killing within the macrophages. Granulomas try to wall off these organisms and prevent their further growth and spread. Many old scourges of mankind like tuberculosis, leprosy and syphilis fall into this category of diseases. Granuloma formation is also the feature of many of our newer problems like fungal infections, sarcoidosis and Crohn's disease.