Giant Cell in Biology and Pathology

When several different types of cells, typically macrophages type of cells, form a union and often forming a granuloma i.e. an aggregation of macrophages is known as a giant cell. These giant cells play significant roles in both pathological and physiological aspects. The multinucleated giant cells are more specifically focused due to their pathological aspects and include mostly the macrophage aggregates that are part of the immune system. The giant cell which is a common example of the multinucleated giant cells known for their physiological functions includes an osteoclast, a bone tissue cell, which is responsible for the maintenance and repair of bones. 

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The Discovery, Origin and Types of Giant Cells

Osteoclasts are the first types of giant cells that were discovered in 1873. The physiological importance of the osteoblasts as the primarily discovered multinucleated giant cells had been known as they were the cells important for the maintenance and the repairing of the bone tissue. The main function of the osteoclasts is the breaking down of the bone cells and hence is critical especially while remodelling the bones in the vertebral skeleton. With the development of the organ culture in the 1970s and further studies of bone resorption restored in the bone marrow and spleen, transplants have shown that the osteoclasts have the same hematopoietic origin as the macrophages. Not only that, osteoclasts are important from the perspective of the niche necessary for the hematopoiesis and for the negative regulation of T-cells. 

Other types of multinucleated giant cells include Foreign body giant cell, Langhans giant cell, Touton giant cell, Giant cell arteritis, and Reed Sternberg cell. These other types of giant cells can arise from different types of bacteria, diseases and cell formations. Many times a giant cell also develops in cases of infections. These particular mechanisms that lead to their formation have been studied for a long time but haven't been understood fully. The processes of giant cell formation which are commonly observed in the monocytes and macrophages as they combine and aggregate together is still an area of interest and are known to cause problems for the immune system as well. 

Langhans Giant Cell

This giant cell was named after a pathologist in Germany named Theodor Langhans. Just like many of the different kinds of giant cell formations. Often referred to as multinucleated giant cells, this formation is the one in which the nuclei forms either a circle or a semicircle related shape which is similar to the shape of a horseshoe away from the centre of the cell. The main cause of worry with the Langhans giant cell is that it is found to be related to tuberculosis and is also known to occur in many different types of granulomatous diseases.

In case the person is either found to be infected with tuberculosis in the endemic areas or has developed sarcoidosis, then the person is likely to catch this condition. Langhans giant cell is found to be closely related to tuberculosis, syphilis, sarcoidosis and also deep fungal infections. In cases of delayed hypersensitivity, Langhans giant cells occur very frequently. The symptoms of such a condition are fever, weight loss, fatigue, and loss of appetite. 

The origin of this type of giant cell is linked to bacteria that spreads from person to person through the medium of air. There is a close relation between tuberculosis and HIV and so many people who have HIV are also observed to face a hard time fighting off the diseases and sicknesses caused by these conditions. Many of the tests may be performed to treat other related diseases and to obtain the correct diagnosis for Langhans giant cells.

Touton Giant Cell

Sometimes known as the xanthelasmatic giant cell, the Touton giant cells are the giant cells that consist of fused epithelioid macrophages and because of such fusion have multiple nuclei. The nuclei usually form a ring and are surrounded by the foamy cytoplasm. One of the symptoms of this particular giant cell is the foamy cytoplasm that makes the cytoplasm around the nucleus visible. Mostly this giant cell formation is seen in lipid-laden areas in the body and is more commonly known for fat necrosis leading. The formation of Touton giant cells is a common occurrence in men and women between the ages of 37 – 78. Like all the other forms of giant cells, Touton giant cells have much of the same symptoms as any other typical formations of giant cells and they include fever, weight loss, fatigue, and loss of appetite. 

Foreign Body Giant Cell

From the given name, it is clear that foreign body giant cells form whenever a person or a sample under consideration is found to have been exposed to a foreign substance. Exogenous substances include talcor sutures. As observed with other types of giant cells, epithelioid macrophages that fuse together cause the giant cells to form and grow. In this form of giant cell, the nuclei are found to be arranged in an overlapping manner. This giant cell is typically found in tissues because of medical devices, prostheses and biomaterials.

Role of Giant Cells in COVID-19 Patients

The Coronavirus disease 2019 ( COVID-19 ) is caused by a new coronavirus known as SARS-CoV-2. Multinucleated giant cells in patients with such cases have recently been detected in autopsy specimens. During the early phase of 2019 novel coronavirus (COVID-19) pneumonia in two patients with lung cancer, this type of giant cell was found in the pulmonary circulatory system. Another such pathological study also found this type of giant cell in COVID-19 and they were described as “multinucleated syncytial cells”. The morphological analysis showed that multinucleated syncytial cells with atypical enlarged pneumocytes characterized by large nuclei, amphophilic granular cytoplasm, and prominent nucleoli were identified in the intra-alveolar, spaces, showing viral cytopathic-like changes. Interestingly, the viral antigen was detected in the cytoplasm of multinucleated syncytial cells. The viral antigen detected in multinucleated giant cells indicates the presence of the SARS-CoV-2 virus. The infection and pathogenesis of the SARS-CoV-2 virus in the human patient largely remained unknown. A further study to characterize the role of multinucleated giant cells in human immune defence against COVID-19 may lead to more effective therapies.