Editing Club cell

{{Short description|Cell type}}
{{Infobox cell
| Name        = Club cell
| Latin       = exocrinocytus bronchiolaris
| Image       =
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'''Club cells''', also known as '''bronchiolar exocrine cells''',<ref name="PapadakosLachmann2007">{{cite book|author1=Peter J. Papadakos|author2=Burkhard Lachmann|title=Mechanical Ventilation: Clinical Applications and Pathophysiology|url=https://books.google.com/books?id=Fr6Q-xpPSdIC&pg=PA74|accessdate=27 May 2011|date=29 August 2007|publisher=Elsevier Health Sciences|isbn=978-0-7216-0186-1|pages=74–}}</ref> are low columnar/cuboidal [[cell (biology)|cells]] with short [[microvilli]], found in the small airways ([[bronchioles]]) of the [[lung]]s.<ref name="pmid18179694">{{cite journal |vauthors=Atkinson JJ, Adair-Kirk TL, Kelley DG, Demello D, Senior RM |title=Clara cell adhesion and migration to extracellular matrix |journal=Respir. Res. |volume=9 |issue= 1|pages=1 |year=2008 |pmid=18179694 |pmc=2249579 |doi=10.1186/1465-9921-9-1 |doi-access=free }}</ref> They were formerly known as ''Clara cells''.

Club cells are found in the ciliated simple epithelium. These cells may secrete [[glycosaminoglycan]]s to protect the bronchiole lining. Bronchiolar cells gradually increase in number as the number of [[goblet cell]]s decrease.

One of the main functions of club cells is to protect the bronchiolar [[epithelium]]. They do this by secreting a small variety of products, including club cell secretory protein [[uteroglobin]], and a solution similar in composition to [[pulmonary surfactant]]. They are also responsible for detoxifying harmful substances inhaled into the lungs. Club cells accomplish this with [[cytochrome P450]] enzymes found in their [[smooth endoplasmic reticulum]]. Club cells also act as a [[stem cell]], multiplying and differentiating into ciliated cells to regenerate the bronchiolar epithelium.<ref>{{Cite web|url=http://medical-dictionary.thefreedictionary.com/Clara+cell|title = Clara cell}}</ref>

==Function==
The respiratory bronchioles represent the transition from the conducting portion to the respiratory portion of the respiratory system. The narrow channels are usually less than 2&nbsp;mm in diameter and they are lined by a simple cuboidal epithelium, consisting of ciliated cells and non-ciliated club cells, which are unique to bronchioles. In addition to being structurally diverse, club cells are also functionally variable. One major function they carry out is the synthesis and secretion of the material lining the bronchiolar [[lumen (anatomy)|lumen]]. This material includes glycosaminoglycans, proteins such as [[lysozyme]]s, and conjugation of the secretory portion of IgA antibodies. These play an important defensive role, and they also contribute to the degradation of the mucus produced by the upper airways. The heterogeneous nature of the dense granules within the club cell's cytoplasm suggests that they may not all have a secretory function. Some of them may contain lysosomal enzymes, which carry out a digestive role, either in defense: Club cells engulf airborne toxins and break them down via their cytochrome P-450 enzymes (particularly [[CYP4B1]], which is only present in the club cells) present in their smooth endoplasmic reticulum; or in the recycling of secretory products. Club cells are mitotically active. They divide and differentiate to form both ciliated and non-ciliated epithelial cells.

==Clinical significance==
Club cells contain [[tryptase]], which is believed to be responsible for cleaving the [[hemagglutinin]] surface protein of [[influenza A]] virus, thereby activating it and causing the symptoms of flu.<ref name="pmid9707539">
{{cite journal |author=Taubenberger JK |title=Influenza virus hemagglutinin cleavage into HA1, HA2: No laughing matter |journal=Proc. Natl. Acad. Sci. U.S.A. |volume=95 |issue=17 |pages=9713–5 |date=August 1998 |pmid=9707539 |pmc=33880 |doi= 10.1073/pnas.95.17.9713|bibcode=1998PNAS...95.9713T |doi-access=free }}</ref> When the [[Chromosome 11 open reading frame 73|l7Rn6]] protein is disrupted in mice, these mice display severe [[emphysema]] at birth as a result of disorganization of the [[Golgi apparatus]] and formation of aberrant vesicular structures within club cells.<ref name="pmid16157679">
{{cite journal | vauthors = Fernández-Valdivia R, Zhang Y, Pai S, Metzker ML, Schumacher A | title = l7Rn6 Encodes a Novel Protein Required for Clara Cell Function in Mouse Lung Development | journal = Genetics | volume = 172 | issue = 1 | pages = 389–99 |date=January 2006 | pmid = 16157679 | pmc = 1456166 | doi = 10.1534/genetics.105.048736 }}</ref>
Malignant club cells are also seen in bronchioalveolar carcinoma of the lung.
Serum club cell proteins are used as a biomarker of lung permeability.  Exposure to particulate air pollution may compromise the integrity of the lung epithelium and lead to rapid increase in epithelial barrier permeability, as reflected by increased serum club cell concentrations.<ref>Provost EB, Chaumont A, Kicinski M, Cox B, Fierens F, Bernard A, Nawrot TS. “Serum levels of club cell secretory protein (Clara) and short- and long-term exposure to particulate air pollution in adolescents” Environ Int. 2014 Apr 4;68C:66-70. doi: 10.1016/j.envint.2014.03.011.</ref>

==History==
=== Name change ===
Club cells were previously called ''Clara cells'', as they were first described by [[Max Clara]] (1899–1966), in 1937. Clara was an active member of the [[Nazi Party]] and used tissue taken from executed victims of [[Nazi Germany]] for his research—including the work that led to his discovery of Clara cells.<ref>
{{cite journal |last1=Winkelmann |first1=Andreas |last2=Noack |first2=Thorsten |year=2010 |title=The Clara cell - a "Third Reich eponym"? |journal=European Respiratory Journal |volume=  36|pmid=20223917|issue= 4|pages= 722–7|url=http://erj.ersjournals.com/cgi/content/abstract/09031936.00146609v1 |doi=10.1183/09031936.00146609 |doi-access=free |url-access=subscription }}</ref> 
In May 2012, the editorial boards of most of the major respiratory journals (including the journals of the [[American Thoracic Society]], the [[European Respiratory Society]] and the [[American College of Chest Physicians]]) concluded that the continued use of Clara's [[eponym]] would be equivalent to honoring him; they therefore introduced a name-change policy, which went into effect beginning January 1, 2013.<ref>
{{cite journal|last=Irwin|first=RS|author2=Augustyn N|author3=French CT|author4=Rice J|author5=Tedeschi V|author6=Welch SJ|title=Spread the word about the journal in 2013: from citation manipulation to invalidation of patient-reported outcomes measures to renaming the Clara cell to new journal features|journal=Chest|year=2013|volume=143|issue=1|pages=1–5|pmid=23276834|url=https://journal.chestnet.org/article/S0012-3692(13)60001-X/fulltext|doi=10.1378/chest.12-2762|url-access=subscription}}</ref>
The term "Clara" was used parenthetically after "club cell" for a 2-year period, after which "Clara cell" and "Clara cell secretory protein" were conclusively replaced with "club cell" and "club cell secretory protein", respectively.<ref>{{cite journal|last=Akram|first=KM|author2=Lomas NJ|author3=Spiteri MA|author4=Forsyth NR|title=Club cells inhibit alveolar epithelial wound repair via TRAIL-dependent apoptosis|journal=Eur Respir J|year=2013|volume=41|issue=3|pages=683–694|doi=10.1183/09031936.00213411|pmid=22790912|doi-access=free}}</ref>

== See also ==

* [[cGMP-dependent protein kinase]]
* [[List of medical eponyms with Nazi associations]], eg. Clara cells
* {{annotated link|Skatole}}
*[[List of human cell types derived from the germ layers]]
*[[List of distinct cell types in the adult human body]]

== References ==
{{Reflist}}

==External links==
* {{BUHistology|13805loa}}
* {{UIUCHistologySubject|1385}}
* [https://web.archive.org/web/20060913082508/http://pathhsw5m54.ucsf.edu/case24/image245.html Histology at ucsf.edu]

{{Lower respiratory system anatomy}}
{{Authority control}}

[[Category:Lung anatomy]]
[[Category:Surfactant secreting cells]]
[[Category:Animal cells]]
[[Category:Human cells]]
[[Category:Nazi human subject research]]