Plasma cell
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[[Image:Plasmacell.jpg|thumb|Plasma cell]]
'''Plasma cells''' (also called '''plasma B cells''' or '''plasmocytes''') are cells of the [[immune system]] that secrete large amounts of [[antibody|antibodies]]. They differentiate from [[B lymphocyte|B cells]] upon stimulation by [[CD4+ lymphocytes]]. The B cell acts as an [[antigen presenting cell]] (APC), consuming an offending [[pathogen]]. That pathogen gets taken up by the B cell by receptor mediated endocytosis, and broken down within these endosomes after fusion with [[lysosome]]s releasing proteolytic enzymes onto the pathogen. Once the enzymes break down the pathogen, pieces of the pathogen (which are now known as antigenic peptides) are loaded onto [[MHC II]] molecules, and presented on its extracellular surface. Once on the extracellular surface, the CD4+ T-helper lymphocyte will bind to the MHC II/Antigen molecule and cause activation of the B cell, which includes differentiation into a plasma cell, and subsequent generation of antibody against the consumed pathogen.
== Overview ==
After dividing for around five days, mature B cells differentiate into either plasma B cells or [[memory B cell]]s. Plasma B cells originate in the [[bone marrow]], then travel to the [[spleen]] or [[lymph nodes]] to secrete antibodies (approximately 10,000 per second). During the initial stages of an immune response the lifespan of plasma cells is very short, typically only a few days to weeks. However, following the process of affinity maturation, plasma cells can survive for months to years and continue to secrete high levels of antibodies. Memory B cells tend to be longer-lived and can therefore respond quickly upon second exposure to an antigen.
The class of antibody that a plasma cell produces depends on signals, called [[cytokine]]s, from other immune system cells, such as [[macrophage]]s and [[T helper cell]]s. This process is called isotype-switching. For example, plasma cells will likely secrete [[IgG3]] antibodies if they matured in the presence of the cytokine [[interferon-gamma]]. Since B cell maturation also involves [[somatic hypermutation]], these antibodies have a very high affinity for their antigen.
== Microscopic anatomy ==
Plasma cells are large lymphocytes with a considerable [[cell nucleus|nucleus]]-to-[[cytoplasm]] ratio and a characteristic appearance on [[light microscopy]]. They have [[basophilic]] cytoplasm and an eccentric nucleus with [[heterochromatin]] in a characteristic [[cartwheel]] arrangement. Their cytoplasm also contains a pale zone that on [[electron microscopy]] contains an extensive [[Golgi apparatus]] and [[centriole]]s ([http://www.stritch.luc.edu/lumen/meded/Histo/HistoImages/hl2A-33.jpg EM picture]). Abundant [[rough endoplasmic reticulum]] combined with a well-developed Golgi apparatus makes plasma cells well-suited for secreting immunoglobulins.
==Role in disease==
[[Cancer]] of plasma cells is termed [[multiple myeloma]]. This condition is frequently identified because malignant plasma cells continue producing an antibody, which can be detected as a [[paraprotein]].
[[Common variable immunodeficiency]] is thought to be due to a problem in the [[cellular differentiation|differentiation]] from lymphocytes to plasma cells. The result is a low serum antibody level and risk of infections.
==External links==
* {{BUHistology|21001loa}}
* {{eMedicineDictionary|plasma+cell}}
* {{Dorlands|c_18|12224615}}
* [http://www.wadsworth.org/chemheme/heme/microscope/plasmacell.htm Histology at wadsworth.org]
{{Cell-biology-stub}}
{{Blood}}
{{Immune system}}
[[Category:Lymphocytes]]
[[ca:Plasmòcit]]
[[de:Plasmazelle]]
[[es:Célula plasmática]]
[[fr:Plasmocyte]]
[[ko:플라즈마 세포]]
[[it:Plasmacellula]]
[[lt:Plazminės ląstelės]]
[[nl:Plasmacel]]
[[ja:形質細胞]]
[[pl:Komórka plazmatyczna]]
[[pt:Plasmócito]]
[[sk:Plazmatická bunka]]
[[sr:Плазмоцит]]
[[sv:Plasmacell]]
[[tr:Plazma hücresi]]
[[zh:浆细胞]]