Giant Cells

GIANT CELLS, cells that exceed in size the ordinary types of cells. The concept of G. c. is not entirely precise: sometimes it is impossible to establish a definite boundary between large and giant cells. G. c. occur both under normal and pathological conditions. G. c. found in normal tissues are divided into two main types: 1) with one large, often polymorphic nucleus (megakaryocytes) and 2) with many nuclei (polycaryocytes). The first type arises through abortive mitosis (often multipolar) and is always found in islands of myeloid hematopoiesis: in the red bone marrow, embryonic liver and spleen, and additionally in the placenta. The multinucleated forms (Koelliker's osteoclasts, Robin's myeloplaxes) produce resorption of bone trabeculae and probably arise through the fusion of many small cells (osteoblasts). Large macrophages (gigantophages) of the spleen also approach the size of G. c. Under pathological conditions, G. c. are found mainly in regenerative and inflammatory processes, especially in productive inflammation and particularly in tuberculosis, as well as in tumors (see Sarcoma and Epulides). Almost all G. c. found under pathological conditions are multinucleated; the exception consists of Sternberg cells, which occur in lymphogranulomatosis and sometimes have one large polymorphic nucleus, and giant cells that are sometimes found in epithelial malignant tumors and which are sometimes, perhaps not entirely correctly, also called giant cells. It is generally believed that nuclear division in G. c. occurs amitotically. The number of nuclei can be very large, sometimes exceeding one hundred. Genetically, G. c. can arise from various types of cells: from squamous and cylindrical epithelium, from muscle tissue, from endothelium, from connective tissue cells - polyblasts, plasma cells, and from lymphocytes. The formation of multinucleated G. c. from ordinary cells can occur in two ways: through repeated nuclear division, where nuclear division is not accompanied by division of the entire cell but only by an increase in its volume, or through the fusion of several homogeneous cells into one. Cells formed by the first method are called "proliferative" or plasmodium, while the second type are called "conglutinative" or syncytium. Among the most frequently occurring giant cells under pathological conditions, two main types can be distinguished by external form. The first is the so-called Langhans type, most commonly found in tuberculous granulomas. The second type, found in the resorption of foreign bodies in tissues, is the so-called "foreign body giant cells" (Fremdkörperriesenzellen). Langhans cells are usually of regular oval or round shape, with homogeneous or slightly granular protoplasm and a very characteristic peripheral arrangement of nuclei. In the center of the cell, Koch's bacilli or fragments of elastic fibers can sometimes be found. Histogenetically, Langhans cells originate from epithelioid cells or from endothelium. There is a view that Langhans cells are nothing other than abortive newly formed vessels in which the nuclei of the endothelium have been preserved on the periphery. Some authors (Maximov, Timofeyevsky) derive these cells from monocytes and polyblasts. Although Langhans cells are also found in other granulomas (leprosy, syphilis, etc.), their diagnostic value for tuberculosis is still great. The second type - multinucleated G. c. formed around foreign bodies - differs from the Langhans type in its irregular shape and different arrangement of nuclei. The shape of such cells depends almost entirely on the foreign body around which they form; if the foreign body is small, it may be located inside the cell, giving it the shape that the foreign body itself has. If the cells are round, their nuclei are distributed quite evenly in the protoplasm, but if they are closely adjacent to the foreign body, the nuclei are pushed to the periphery, and the part of the cell adjacent to the foreign body is devoid of nuclei. These cells arise from mesenchymal elements and sometimes from epithelium. The function of G. c. consists in the resorption and "digestion" of foreign bodies and generally of formations foreign to the living organism, such as, for example, necrotized dense tissues. G. c. of the cerebral cortex - see Betz cells.