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<p><b>New page</b></p><div>== Alpha Defensin ==<br />
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[[File:PDB_1dfn_EBI.jpg|thumb|right|300px|Structure of Alpha Defensin]]<br />
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'''Alpha defensins''' are a class of [[antimicrobial peptides]] that play a crucial role in the [[innate immune system]]. They are small, cationic peptides that are primarily found in [[neutrophils]] and [[Paneth cells]] of the [[small intestine]]. Alpha defensins are known for their ability to disrupt the [[cell membrane]]s of [[microorganisms]], thereby providing a first line of defense against [[infection]].<br />
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== Structure ==<br />
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Alpha defensins are characterized by their three-dimensional structure, which includes a triple-stranded [[beta-sheet]] and a conserved [[cysteine]] motif that forms three [[disulfide bonds]]. This structure is essential for their stability and function. The image on the right shows the structure of an alpha defensin, highlighting its compact and stable configuration.<br />
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== Function ==<br />
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The primary function of alpha defensins is to protect the host from [[pathogens]]. They achieve this by:<br />
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* Disrupting microbial membranes, leading to cell lysis.<br />
* Modulating the [[immune response]] by acting as [[chemotactic agents]] for [[immune cells]].<br />
* Neutralizing [[bacterial toxins]].<br />
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Alpha defensins are effective against a broad range of pathogens, including [[bacteria]], [[fungi]], and [[viruses]].<br />
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== Expression and Regulation ==<br />
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Alpha defensins are expressed in specific cell types:<br />
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* '''Neutrophils''': These [[white blood cells]] contain alpha defensins in their [[azurophilic granules]], which are released upon activation.<br />
* '''Paneth cells''': Located in the [[crypts of Lieberkühn]] in the small intestine, these cells secrete alpha defensins into the intestinal lumen, contributing to [[gut immunity]].<br />
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The expression of alpha defensins is regulated by various factors, including [[cytokines]] and [[microbial products]].<br />
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== Clinical Significance ==<br />
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Alpha defensins have been implicated in several clinical conditions:<br />
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* '''Infectious diseases''': Deficiencies or dysfunctions in alpha defensins can lead to increased susceptibility to infections.<br />
* '''Inflammatory diseases''': Overexpression of alpha defensins has been associated with inflammatory conditions such as [[Crohn's disease]].<br />
* '''Cancer''': Altered levels of alpha defensins have been observed in certain types of [[cancer]], suggesting a potential role in tumorigenesis.<br />
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== Related Pages ==<br />
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* [[Beta defensin]]<br />
* [[Innate immune system]]<br />
* [[Antimicrobial peptide]]<br />
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[[Category:Immunology]]<br />
[[Category:Peptides]]</div>Prab