The term giant cells comes from histology or pathology. Giant cells are cells that are greatly enlarged and have multiple nuclei.
What are giant cells?
In histology and pathology, the term giant cell refers to a cell that is very large compared to other cells. Giant cells usually have multiple nuclei. These may be misshapen or lobulated. Three forms of giant cells can be distinguished. The first group occurs physiologically. The second group results from cell division disorders, and the third group is found in neoplasms.
Anatomy and structure
Physiologically occurring cells include osteoclasts. Osteoclasts are multinucleated cells of bone. They arise from bone marrow-derived progenitor cells and belong to the so-called mononuclear system (MPS). Osteoclasts have a diameter of 50 to 100 µm. A single osteoclast can contain up to ten cell nuclei. The cells are located on the surface of the bones in special lacunae. Langhans cells also belong to the giant cells. They develop from the reticuloendothelial system (RES). The Langerhans giant cells have a diameter of up to 0.3 millimeters and are found in various locations in the body. Typical of these cells are their many nuclei, which are arranged in a horseshoe shape. Megakaryocytes are found in the bone marrow. They also belong to the physiological giant cells. They develop from the megakaryoblasts and are up to 15 times larger than red blood cells. However, only about one percent of all bone marrow cells are megakaryocyte-type cells. Megakaryocytes have only one cell nucleus. However, this is very irregularly shaped and is also segmented many times, so that it can give the impression that there are several cell nuclei.
Function and tasks
Depending on the cell type, giant cells perform different tasks. Osteoclasts are responsible for the breakdown of bone substance. For this purpose, the cells have two mechanisms at their disposal. First, they dissolve mineral salts from the bone with the help of a lowered pH. Secondly, they release enzymes that dissolve the collagen matrix of the bone. They then eat (phagocytose) the released collagen particles. The activity of osteoclasts is regulated by the hormones parathyroid hormone and calcitonin. A kind of counterpart of the osteoclasts are the osteoblasts. They build up bone substance. The role of Langhans cells is not yet completely understood. They seem to play a role in the phagocytosis of certain antigens. For example, they appear in the context of tuberculosis. The causative agent of tuberculosis, Mycobacterium tuberculosis, has a waxy cell wall, so it cannot be rendered harmless by the body’s normal phagocytic cells, the macrophages. The mycobacteria are taken up by the phagocytes. But since they cannot be destroyed, the body forms a protective wall of phagocytes around the macrophages that contain the pathogens. These scavenger cells are also called epithelioid cells. They are joined by lymphocytes and also Langhans giant cells. They ensure that the mycobacteria remain in place and are not scattered throughout the body. Megakaryocytes belong to the blood-forming cells of the bone marrow. As part of thrombopoiesis, megakaryocytes form platelets. In this process, a single megakaryocyte can release up to a thousand platelets. Thrombocytes are blood platelets. They play an important role in blood clotting.
Diseases
An example of a pathologic giant cell is Sternberg-Reed giant cells. Sternberg-Reed giant cells are up to 45 μm in diameter. They are a diagnostic criterion for Hodgkin lymphoma. These giant cells are neoplastic derivatives of B lymphocytes. Hodgkin’s lymphoma is a malignant lymphoid disease. Most patients develop the disease around the age of 25 or around the age of 60. As a rule, Hodgkin’s lymphoma is initially manifested by non-specific symptoms such as night sweats or weight loss. The so-called Pel-Ebstein fever is typical. This is a wave-like fever. Fever phases of three to ten days alternate with fever-free phases. In addition, there is swelling of the lymph nodes or the spleen. A characteristic feature of the disease is lymph node pain after alcohol consumption.However, this alcohol pain occurs in only about a quarter of all patients. If alcohol pain is present, however, the diagnosis of Hodgkin’s lymphoma is very obvious. The foreign body giant cells also belong to the pathological giant cells. They are macrophages that form around a foreign body. Such foreign body giant cells are found, for example, in foreign body granulomas in silicosis. Silicosis is also known as silica dust lung. It results from long-term inhalation of fine dust and belongs to the so-called pneumoconioses. Silicosis is a typical disease of miners. The body builds granulomas around the inhaled particles. In addition, the lung tissue is partially transformed into connective tissue. As a result, the surface area of the lungs becomes smaller and smaller, and oxygen uptake is severely restricted. The damaged lung is also much more susceptible to diseases such as tuberculosis or lung cancer. Giant cells are also found in giant cell arteritis. The disease is also known as arteritis temporalis. The triggers of the disease are still unknown. Inflammation occurs in the vessel walls of arteries in the head. The leading symptoms of giant cell arteritis are headaches, pain when chewing and hypersensitivity of the scalp. About 70 percent of all patients also complain of visual disturbances. Therapy is with cortisone preparations.
