Degranulation
{{Short description|Process by which cells lose secretory granules}}
Image:Allergy degranulation processes 01.svg; 2 = IgE; 3 = FcεR1; 4 = preformed mediators (histamine, proteases, chemokines, heparin); 5 = granules; 6 - Mast cell; 7 - newly formed mediators (prostaglandins, leukotrienes, thromboxanes, platelet-activating factor)]]
Degranulation is a cellular process that releases antimicrobial, cytotoxic, or other molecules from secretory vesicles called granules found inside some cells. It is used by several different cells involved in the immune system, including granulocytes (neutrophils, basophils, eosinophils, and mast cells). It is also used by certain lymphocytes such as natural killer (NK) cells and cytotoxic T cells, whose main purpose is to destroy invading microorganisms.
Mast cells
Degranulation in mast cells is part of an inflammatory response, and substances such as histamine are released. Granules from mast cells mediate processes such as "vasodilation, vascular homeostasis, innate and adaptive immune responses, angiogenesis, and venom detoxification."{{Cite journal |last1=Krystel-Whittemore |first1=Melissa |last2=Dileepan |first2=Kottarappat N. |last3=Wood |first3=John G. |date=2016 |title=Mast Cell: A Multi-Functional Master Cell |journal=Frontiers in Immunology |volume=6 |page=620 |doi=10.3389/fimmu.2015.00620 |pmid=26779180 |pmc=4701915 |issn=1664-3224 |doi-access=free }}
Antigens interact with IgE molecules already bound to high affinity Fc receptors on the surface of mast cells to induce degranulation, via the activation of tyrosine kinases within the cell. The mast cell releases a mixture of compounds, including histamine, proteoglycans, serotonin, and serine proteases from its cytoplasmic granules.{{cite journal |vauthors=Yamasaki S, Saito T |title=Regulation of mast cell activation through FcepsilonRI |journal=Chem Immunol Allergy |volume=87 |pages=22–31 |year= 2005|pmid=16107760 |doi=10.1159/000087568 |series=Chemical Immunology and Allergy |isbn=3-8055-7948-9}}
Eosinophils
In a similar mechanism, activated eosinophils release preformed mediators such as major basic protein, and enzymes such as peroxidase, following interaction between their Fc receptors and IgE molecules that are bound to large parasites like helminths.{{cite journal |vauthors=David J, Butterworth A, Vadas M |title=Mechanism of the interaction mediating killing of Schistosoma mansoni by human eosinophils |journal=Am J Trop Med Hyg |volume=29 |issue=5 |pages=842–8 |year=1980 |pmid=7435788 |doi=10.4269/ajtmh.1980.29.842}}{{cite journal |vauthors=Capron M, Soussi Gounni A, Morita M, Truong M, Prin L, Kinet J, Capron A |title=Eosinophils: from low- to high-affinity immunoglobulin E receptors |journal=Allergy |volume=50 |issue=25 Suppl |pages=20–23 |year=1995 |pmid=7677229 |doi=10.1111/j.1398-9995.1995.tb04270.x|s2cid=36197719 |url=https://zenodo.org/record/1230625 }}
Neutrophils
Degranulation in neutrophils can occur in response to infection, and the resulting granules are released in order to protect against tissue damage. Excessive degranulation of neutrophils, sometimes triggered by bacteria, is associated with certain inflammatory disorders, such as asthma and septic shock.{{Cite journal |last1=Gierlikowska |first1=Barbara |last2=Stachura |first2=Albert |last3=Gierlikowski |first3=Wojciech |last4=Demkow |first4=Urszula |date=2021 |title=Phagocytosis, Degranulation and Extracellular Traps Release by Neutrophils—The Current Knowledge, Pharmacological Modulation and Future Prospects |journal=Frontiers in Pharmacology |volume=12 |doi=10.3389/fphar.2021.666732 |pmid=34017259 |pmc=8129565 |issn=1663-9812 |doi-access=free }}{{Cite journal |last=Lacy |first=Paige |date=2006-09-15 |title=Mechanisms of Degranulation in Neutrophils |journal=Allergy, Asthma & Clinical Immunology |volume=2 |issue=3 |pages=98–108 |doi=10.1186/1710-1492-2-3-98 |issn=1710-1492 |pmc=2876182 |pmid=20525154 |doi-access=free }}
Four kinds of granules exist in neutrophils that display differences in content and regulation. Secretory vesicles are the most likely to release their contents by degranulation, followed by gelatinase granules, specific granules, and azurophil granules.{{cite journal |vauthors=Faurschou M, Borregaard N |title=Neutrophil granules and secretory vesicles in inflammation |journal=Microbes Infect |volume=5 |issue=14 |pages=1317–1327 |year=2003 |pmid=14613775 |doi=10.1016/j.micinf.2003.09.008}}
Cytotoxic T cells and NK cells
Cytotoxic T cells and NK cells release molecules like perforin and granzymes by a process of directed exocytosis to kill infected target cells.{{cite journal |vauthors=Veugelers K, Motyka B, Frantz C, Shostak I, Sawchuk T, Bleackley R |s2cid=23814556 |title=The granzyme B-serglycin complex from cytotoxic granules requires dynamin for endocytosis |journal=Blood |volume=103 |issue=10 |pages=3845–3853 |year=2004 |pmid=14739229 |doi=10.1182/blood-2003-06-2156|doi-access=free }}
See also
References
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External links
- {{MeshName|Cell+Degranulation}}
{{Membrane transport}}