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Paneth cells

Paneth cells are found in the intestinal tract. They contain zinc and lysozyme (an enzyme that lyses certain kinds of bacteria) as well as large eosinophilic refractile granules within their apical cytoplasm. Their exact function is unknown but due to the presence of lysozyme it is likely that Paneth cells contribute to host defense. When exposed to bacteria or bacterial antigens, Paneth cells secrete a number lysozymes into the lumen of the crypt, thereby contributing to maintenance of the gastrointestinal barrier. Paneth cells are named after Joseph Paneth (1857–1890), Austrian physician.

Contents

Stem cells

Small intestinal crypts house stem cells that serve to constantly replenish epithelial cells that die and are lost from the villi.

Protection of these stem cells is essential for long-term maintenance of the intestinal epithelium, and the location of Paneth cells adjacent to stem cells suggests that they play a critical role in defending epithelial cell renewal.

Sensing microbiota

Paneth cells sense bacteria via MyD88-dependent toll-like receptor (TLR) activation which then triggers antimicrobial action.[1]

Secretions

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Defensins

The principal defense molecules secreted by Paneth cells are alpha-defensins, also known as cryptdins.[1] These peptides have hydrophobic and positively-charged domains that can interact with phospholipids in cell membranes. This structure allows defensins to insert into membranes, where they interact with one another to form pores that disrupt membrane function, leading to cell lysis. Due to the higher concentration of negatively-charged phospholipids in bacterial than vertebrate cell membranes, defensins preferentially bind to and disrupt bacterial cells, sparing the cells they are functioning to protect.[2]

Paneth cells are stimulated to secrete defensins when exposed to bacteria (both Gram positive and negative types) or such bacterial products as lipopolysaccharide, muramyl dipeptide and lipid A.

Other secretions

In addition to defensins, Paneth cells secrete lysozyme and phospholipase A2, both of which have clear antimicrobial activity. This battery of secretory molecules gives Paneth cells a potent arsenal against a broad spectrum of agents, including bacteria, fungi and even some enveloped viruses.

References

  1. ^ Wilson C, Ouellette A, Satchell D, Ayabe T, López-Boado Y, Stratman J, Hultgren S, Matrisian L, Parks W (1999). "Regulation of intestinal alpha-defensin activation by the metalloproteinase matrilysin in innate host defense.". Science 286 (5437): 113–7. doi:10.1126/science.286.5437.113. PMID 10506557.  
  2. ^ Ayabe T, Satchell D, Wilson C, Parks W, Selsted M, Ouellette A (2000). "Secretion of microbicidal alpha-defensins by intestinal Paneth cells in response to bacteria.". Nat Immunol 1 (2): 113–8. doi:10.1038/77783. PMID 11248802.  

Further reading

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