Editing Crohn's disease (section)

=== Immune system ===
There was a prevailing view that Crohn's disease is a primary [[T cell]] autoimmune disorder; however, a newer theory hypothesizes that Crohn's results from an impaired innate immunity.<ref>{{cite journal | vauthors = Marks DJ, Segal AW | title = Innate immunity in inflammatory bowel disease: a disease hypothesis | journal = The Journal of Pathology | volume = 214 | issue = 2 | pages = 260–266 | date = January 2008 | pmid = 18161747 | pmc = 2635948 | doi = 10.1002/path.2291 }}</ref> The later hypothesis describes impaired [[cytokine]] secretion by [[macrophage]]s, which contributes to impaired innate immunity and leads to a sustained microbial-induced inflammatory response in the colon, where the bacterial load is high.<ref name="Bact08" /><ref name="Marks2006" /> Another theory is that the inflammation of Crohn's was caused by an overactive [[Th2 cells|T<sub>h</sub>1]] and [[Th17|T<sub>h</sub>17]] [[cytokine]] response.<ref>{{cite journal | vauthors = Cobrin GM, Abreu MT | title = Defects in mucosal immunity leading to Crohn's disease | journal = Immunological Reviews | volume = 206 | issue = 1 | pages = 277–295 | date = August 2005 | pmid = 16048555 | doi = 10.1111/j.0105-2896.2005.00293.x | s2cid = 37353838 }}</ref><ref>{{cite journal | vauthors = Elson CO, Cong Y, Weaver CT, Schoeb TR, McClanahan TK, Fick RB, Kastelein RA | title = Monoclonal anti-interleukin 23 reverses active colitis in a T cell-mediated model in mice | journal = Gastroenterology | volume = 132 | issue = 7 | pages = 2359–2370 | date = June 2007 | pmid = 17570211 | doi = 10.1053/j.gastro.2007.03.104 }}</ref>

In 2007, the ATG16L1 gene was implicated in Crohn's disease, which may induce [[Autophagy (cellular)|autophagy]] and hinder the body's ability to attack invasive bacteria.<ref name="Prescott NJ, Fisher SA, Franke A, Hampe J, Onnie CM, Soars D, Bagnall R, Mirza MM, Sanderson J, Forbes A, Mansfield JC, Lewis CM, Schreiber S, Mathew CG 2007 1665–71" /> Another study theorized that the human immune system traditionally evolved with the presence of [[parasite]]s inside the body and that the lack thereof due to modern hygiene standards has weakened the immune system. Test subjects were reintroduced to harmless parasites, with positive responses.<ref>{{cite news |url=https://www.nytimes.com/2008/06/29/magazine/29wwln-essay-t.html |work=[[The New York Times]] |title=The Worm Turns |vauthors=Velasquez-Manoff M |date=June 29, 2008 |url-status=live |archive-url = https://web.archive.org/web/20170107144610/http://www.nytimes.com/2008/06/29/magazine/29wwln-essay-t.html |archive-date=January 7, 2017}}</ref>