User:Ikeshammah/Giant cell

A giant cell (multinucleated giant cell, multinucleate giant cell) is a mass formed by the union of several distinct cells(usually histiocytes), often forming a granuloma. Although there is typically a focus on the pathological aspects of multinucleate giant cells (MGCs), they also play many important physiological roles. Osteoclasts specifically are invaluable to healthy physiological functions and are key players in the skeletal system. Osteoclasts are frequently classified and discussed separately from other MGCs which are more closely linked with human pathologies.

Non-osteoclast MGCs can arise in response to an infection, such as from tuberculosis, herpes, or HIV, or foreign body. These MGCs are cells of monocyte or macrophage lineage fused together. Similar to their monocyte precursors, they are able to phagocytose foreign materials. However, their large size and extensive membrane ruffling make them better equipped to clear up larger particles. They utilize activated CR3s to ingest complement-opsonized targets. Non-osteoclast MGCs are also responsible for the clearance of cell debris which is necessary for tissue remodeling after injuries.

Types include foreign-body giant cell, Langhans giant cell, Touton giant cells, Giant-cell arteritis, and Reed–Sternberg cell.

History
Osteoclasts were discovered in 1873. However, it wasn't until the development of the organ culture in the 1970’s that their origin and function could be deduced. Although there was a general consensus early on about its function, theories on the origins of osteoclasts was heavily debated. Similar to osteoclasts, osteoblasts were typically found in the bone. This led many to believe they came from the same progenitor cell. Because of this, osteoclasts were thought to be derived from cells in connective tissue. Studies that observed that bone resorption in a model of osteoporosis could be restored bone marrow and spleen transplants, helped prove osteoclasts hematopoietic origin.

Other multinucleated giant cell formations can arise from numerous types of bacteria, diseases, and cell formations. Giant cells are known to develop when infections are also present. They were first noticed as early as the middle of the last century, but still it is not fully understood why these reactions occur. In the process of giant cell formation, monocytes or macrophages fuse together, which could cause multiple problems for the immune system.

Osteoclast
Osteoclast are the most prominent example of an MGC and are responsible for the resorption of bone in the body. Like other MGCs they are formed from the fusion of Monocyte/Macrophage precursors. However, unlike other MGC, the fusion pathway it originates from is well elucidated.They also do not ingest foreing materials and instead absorb bone matrix and minerals.

Osteoclasts are typically associated more with healthy physiological functions than they are to pathological states. They function alongside osteoclasts to remodel and maintain the integrity of bones in the body. They also contribute to the creation of the niche necessary for hematopoiesis, and negatively regulate T-cells. While Osteoclasts primary functions are integral to maintaining a healthy physiological state, they have also been linked to osteoporosis and the formation of bone tumors.

Reed-Sternberg cell
These cells are generally thought to originate from B-lymphocytes. However, because of how rare these cells are they are hard to study there are other theories about the origins of these cells. Some less popular theories speculate that they may arise from the fusion between reticulum cells, lymphocytes, and virus infected cells.

Similar to other MGCs, Reed Sternberg cells are large and are either multinucleated or have a bilobed nucleus. Their nuclei are irregularly shaped, contain clear chromatin, and possess an eosinophilic nucleolus.