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[[File:Innate immune system.png|thumb|Innate immune system]]
The '''innate,''' or '''nonspecific, immune system''' <ref>{{Cite web|title=Immune response: MedlinePlus Medical Encyclopedia|url=https://medlineplus.gov/ency/article/000821.htm|access-date=2021-11-07|website=medlineplus.gov|language=en}}</ref> is one of the two main immunity strategies (the other being the [[adaptive immune system]]) in [[vertebrate]]s. The innate immune system is an older evolutionary defense strategy, relatively speaking, and is the dominant immune system response found in [[plant]]s, [[fungi]], [[insect]]s, and primitive [[multicellular organisms]] (see [[#Beyond vertebrates|Beyond vertebrates]]).<ref name="Janeway">{{cite book | vauthors = Janeway C, Paul C, Travers M, Walport M, Shlomchik M | author-link = Charles Janeway | title = Immunobiology | edition = Fifth | publisher = Garland Science | year = 2001 | ___location = New York and London| url = https://www.ncbi.nlm.nih.gov/books/bv.fcgi?call=bv.View..ShowTOC&rid=imm.TOC&depth=10| isbn = 0-8153-4101-6}}.</ref>
The major functions of the innate immune system are to:
* identify and remove foreign substances present in organs, tissues, blood and [[lymph]], by specialized [[white blood cells]]
* activate the [[adaptive immune system]] through [[antigen presentation]]
* act as a physical and chemical barrier to infectious agents; via physical measures such as skin and chemical measures such as [[Coagulation|clotting factors]] in blood, which are released following a contusion or other injury that breaks through the first-line physical barrier (not to be confused with a second-line physical or chemical barrier, such as the [[blood-brainblood–brain barrier]], which protects the nervous system from [[pathogens]] that have already gained access to the host).
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| [[human eye|Eye]]s || Tears<ref name=Mayer/>
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|[[Blood-brainBlood–brain barrier]] || [[endothelial cells]] (via passive [[diffusion]]/ [[osmosis]] & active selection). [[P-glycoprotein]] (mechanism by which [[active transport]]ation is mediated)
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* ''[[Histoplasma]]''
* ''[[Cryptococcus (fungus)|Cryptococcus]]''
|| no || yes || yes <ref>{{cite journal | vauthors = Ma LL, Wang CL, Neely GG, Epelman S, Krensky AM, Mody CH | title = NK cells use perforin rather than granulysin for anticryptococcal activity | journal = Journal of Immunology | volume = 173 | issue = 5 | pages = 3357–3365 | date = September 2004 | pmid = 15322199 | doi = 10.4049/jimmunol.173.5.3357 | s2cid = 43258057 | doi-access = free }}</ref>
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