Editing Immune response (section)

== Innate part ==
{{Further|Innate immune system}}
[[File:PAMPs_and_PRRs_in_the_Innate_Immune_System.png|thumb|[[Innate immune response]] to a [[gram-negative bacteria]] invasion]]
The [[Innate immune system|innate immune response]] is an organism's first response to foreign invaders. This immune response is evolutionarily conserved across many different species, with all multi-cellular organisms having some sort of variation of an innate response.<ref name=":0">{{Cite book|last=Punt, Jenni|title=Kuby immunology|others=Stranford, Sharon A.; Jones, Patricia P.; Owen, Judith A.|isbn=978-1464189784|edition=Eighth|location=New York|oclc=1002672752|date=2018}}{{page needed|date=October 2022}}</ref> The innate immune system consists of physical barriers such as [[skin]] and [[mucous membrane]]s, various cell types like [[neutrophil]]s, [[macrophage]]s, and [[monocyte]]s, and soluble factors including [[cytokine]]s and complement.<ref name=":2">{{Cite book|title=Clinical immunology : principles and practice|others=Rich, Robert R.|isbn=978-0702070396|edition=Fifth|location=[St. Louis, Mo.]|oclc=1023865227|date = 2018}}{{page needed|date=October 2022}}</ref> In contrast to the [[adaptive immune response]], the innate response is not specific to any one foreign invader and as a result, works quickly to rid the body of pathogens.{{citation needed|date=July 2022}}

Pathogens are recognized and detected via [[pattern recognition receptor]]s (PRR). These receptors are structures on the surface of macrophages which are capable of binding foreign invaders and thus initiating [[cell signaling]] within the immune cell. Specifically, the PRRs identify [[Pathogen-associated molecular pattern|pathogen-associated molecular patterns (PAMPs)]] which are integral structural components of pathogens. Examples of PAMPs include the [[Peptidoglycan|peptidoglycan cell wall]] or [[lipopolysaccharide]]s (LPS), both of which are essential components of bacteria and are therefore evolutionarily conserved across many different bacterial species.<ref>{{Cite web|url=http://faculty.ccbcmd.edu/courses/bio141/lecguide/unit5/innate/induced%20innate_PAMPs.html|title=The Innate Immune System: Early Induced Innate Immunity: PAMPs|website=faculty.ccbcmd.edu|access-date=2020-03-08|archive-date=2020-02-01|archive-url=https://web.archive.org/web/20200201191046/http://faculty.ccbcmd.edu/courses/bio141/lecguide/unit5/innate/induced%20innate_PAMPs.html|url-status=dead}}</ref>

When a foreign pathogen bypasses the physical barriers and enters an organism, the PRRs on macrophages will recognize and bind to specific PAMPs. This binding results in the activation of a [[signaling pathway]] which allows for the [[transcription factor]] [[NF-κB]] to enter the nucleus of the macrophage and initiate the transcription and eventual secretion of various [[cytokine]]s such as [[Interleukin 8|IL-8]], [[Interleukin-1 family|IL-1]], and [[Tumor necrosis factor alpha|TNFα]].<ref name=":0" /> Release of these cytokines is necessary for the entry of [[neutrophil]]s from the [[blood vessel]]s to the infected tissue. Once neutrophils enter the tissue, like macrophages, they are able to [[phagocytize]] and kill any pathogens or microbes.{{citation needed|date=July 2022}}

[[Complement system|Complement]], another component of the innate immune system, consists of three pathways that are activated in distinct ways. The classical pathway is triggered when IgG or IgM is bound to its target antigen on either the pathogen cell membrane or an antigen-bound antibody. The alternative pathway is activated by foreign surfaces such as viruses, fungi, bacteria, parasites, etc., and is capable of autoactivation due to “tickover” of C3. The [[lectin]] pathway is triggered when [[mannose-binding lectin]] (MBL) or [[ficolin]] aka specific pattern recognition receptors bind to pathogen-associated molecular patterns on the surface of invading microorganisms such as [[yeast]], bacteria, parasites, and viruses.<ref>{{Cite journal|last1=Sarma|first1=J. Vidya|last2=Ward|first2=Peter A.|date=2011|title=The complement system|journal=Cell and Tissue Research|volume=343|issue=1|pages=227–235|doi=10.1007/s00441-010-1034-0|issn=0302-766X|pmc=3097465|pmid=20838815}}</ref> Each of the three pathways ensures that complement will still be functional if one pathway ceases to work or a foreign invader is able to evade one of these pathways ([[defense in depth]] principle).<ref name=":0" /> Though the pathways are activated differently, the overall role of the complement system is to [[opsonize]] pathogens and induce a series of [[inflammatory response]]s that help to combat [[infection]].{{citation needed|date=July 2022}}