Editing Hypersensitivity (section)

{{short description|Overreaction of the immune system to an antigen}}
{{other uses}}
{{refimprove|date=September 2019}}
{{Infobox medical condition (new)
| name            = Hypersensitivity
| image           =2228 Immune Hypersensitivity new.jpg

| caption         =Types of hypersensitivity reactions

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'''Hypersensitivity''' (also called '''hypersensitivity reaction''' or '''intolerance''') is an abnormal physiological condition in which there is an undesirable and adverse [[immune response]] to an [[antigen]].<ref>{{Cite journal |last1=Andreozzi |first1=Laura |last2=Giannetti |first2=Arianna |last3=Cipriani |first3=Francesca |last4=Caffarelli |first4=Carlo |last5=Mastrorilli |first5=Carla |last6=Ricci |first6=Giampaolo |date=2019 |title=Hypersensitivity reactions to food and drug additives: problem or myth? |url=https://www.mattioli1885journals.com/index.php/actabiomedica/article/view/8168 |journal=Acta Bio-Medica |volume=90 |issue=3–S |pages=80–90 |doi=10.23750/abm.v90i3-S.8168 |issn=2531-6745 |pmc=6502174 |pmid=30830065}}</ref><ref>{{Cite journal |last1=Gargano |first1=Domenico |last2=Appanna |first2=Ramapraba |last3=Santonicola |first3=Antonella |last4=De Bartolomeis |first4=Fabio |last5=Stellato |first5=Cristiana |last6=Cianferoni |first6=Antonella |last7=Casolaro |first7=Vincenzo |last8=Iovino |first8=Paola |date=2021 |title=Food Allergy and Intolerance: A Narrative Review on Nutritional Concerns |journal=Nutrients |volume=13 |issue=5 |pages=1638 |doi=10.3390/nu13051638 |issn=2072-6643 |pmc=8152468 |pmid=34068047 |doi-access=free }}</ref> It is an abnormality in the [[immune system]] that causes [[Immune disorder|immune diseases]] including [[allergies]] and [[autoimmunity]]. It is caused by many types of particles and substances from the external environment or from within the body that are recognized by the [[immune cell]]s as antigens.<ref>{{Cite journal |last=Dispenza |first=Melanie C. |date=2019 |title=Classification of hypersensitivity reactions |url=https://allergolyon.fr/wp-content/uploads/2020/08/0.4-Classification-of-hypersensitivity-reactions-2019.pdf |journal=Allergy and Asthma Proceedings |volume=40 |issue=6 |pages=470–473 |doi=10.2500/aap.2019.40.4274 |issn=1539-6304 |pmid=31690397|s2cid=207891282 }}</ref> The immune reactions are usually referred to as an over-reaction of the immune system and they are often damaging and uncomfortable.<ref>{{Cite journal |last1=Tian |first1=Bao-Ping |last2=Zhou |first2=Hong-Bin |last3=Xia |first3=Li-Xia |last4=Shen |first4=Hua-Hao |last5=Ying |first5=Songmin |date=2014 |title=Balance of apoptotic cell death and survival in allergic diseases |url=https://www.sciencedirect.com/science/article/abs/pii/S1286457914000914 |journal=Microbes and Infection |volume=16 |issue=10 |pages=811–821 |doi=10.1016/j.micinf.2014.07.004 |issn=1769-714X |pmid=25111826|doi-access=free }}</ref>

In 1963, [[Philip George Houthem Gell]] and [[Robin Coombs]] introduced a systematic classification of the different types of hypersensitivity based on the types of antigens and immune responses involved.<ref>{{Cite journal |last=Silverstein |first=Arthur M. |date= |title=Philip George Houthem Gell. 20 October 1914 – 3 May 2001 Elected FRS 1969 |url=https://royalsocietypublishing.org/doi/10.1098/rsbm.2003.0010 |journal=Biographical Memoirs of Fellows of the Royal Society |language=en |volume=49 |pages=163–178 |doi=10.1098/rsbm.2003.0010 |issn=0080-4606|url-access=subscription }}</ref> According to this system, known as the [[#Gell and Coombs classification|Gell and Coombs classification]]<ref>{{Cite journal |last1=Descotes |first1=J. |last2=Choquet-Kastylevsky |first2=G. |date=2001-02-02 |title=Gell and Coombs's classification: is it still valid? |url=https://www.sciencedirect.com/science/article/abs/pii/S0300483X00004005 |journal=Toxicology |volume=158 |issue=1–2 |pages=43–49 |doi=10.1016/s0300-483x(00)00400-5 |issn=0300-483X |pmid=11164991|url-access=subscription }}</ref> or Gell-Coombs's classification,<ref>{{Cite journal |last=Rajan |first=T. V. |date=2003 |title=The Gell-Coombs classification of hypersensitivity reactions: a re-interpretation |url=https://www.cell.com/trends/immunology/fulltext/S1471-4906(03)00142-X?_returnURL=https%3A%2F%2Flinkinghub.elsevier.com%2Fretrieve%2Fpii%2FS147149060300142X%3Fshowall%3Dtrue |journal=Trends in Immunology |volume=24 |issue=7 |pages=376–379 |doi=10.1016/s1471-4906(03)00142-x |issn=1471-4906 |pmid=12860528|url-access=subscription }}</ref> there are four types of hypersensitivity, namely: [[Type I hypersensitivity|type I]], which is an [[Immunoglobulin E]] (IgE) mediated immediate reaction; [[Type II hypersensitivity|type II]], an antibody-mediated reaction mainly involving [[IgG]] or [[IgM]]; [[Type III hypersensitivity|type III]], an immune complex-mediated reaction involving [[IgG]], [[complement system]] and [[phagocytes]]; and [[Type IV hypersensitivity|type IV]], a cytotoxic, cell-mediated, delayed hypersensitivity reaction involving [[T cells]].<ref name="TypeIII">{{Citation|last1=Usman|first1=Norina|title=Type III Hypersensitivity Reaction|date=2021|url=http://www.ncbi.nlm.nih.gov/books/NBK559122/|work=StatPearls|place=Treasure Island (FL)|publisher=StatPearls Publishing|pmid=32644548|access-date=2021-07-05|last2=Annamaraju|first2=Pavan}} {{CC-notice|cc=by4}}</ref>

The first three types are considered immediate hypersensitivity reactions because they occur within 24 hours. The fourth type is considered a delayed hypersensitivity reaction because it usually occurs more than 12 hours after exposure to the allergen, with a maximal reaction time between 48 and 72 hours.<ref name=":3">{{Citation|last1=Marwa|first1=Khaled|title=Type IV Hypersensitivity Reaction|date=2021|url=http://www.ncbi.nlm.nih.gov/books/NBK562228/|work=StatPearls|place=Treasure Island (FL)|publisher=StatPearls Publishing|pmid=32965899|access-date=2021-07-05|last2=Kondamudi|first2=Noah P.}} {{CC-notice|cc=by4}}</ref> Hypersensitivity is a common occurrence: it is estimated that about 15% of humans have at least one type during their lives, and has increased since the latter half of the 20th century.<ref name=":4" />