Editing Immune response (section)

{{Short description|Reaction occurring within an organism as a defence against a pathogen}}
An '''immune response''' is a physiological reaction which occurs within an organism in the context of [[inflammation]] for the purpose of defending against exogenous factors. These include a wide variety of different [[toxin]]s, [[virus]]es, intra- and extracellular [[bacteria]], [[protozoa]], [[Parasitic worm|helminths]], and [[Fungus|fungi]] which could cause serious problems to the health of the host organism if not cleared from the body.<ref name=":1">{{Cite book|last=Sompayrac, Lauren|title=How the immune system works|date= 2019|isbn=978-1119542193|edition=Sixth|location=Hoboken, NJ|oclc=1083704429}}{{page needed|date=October 2022}}</ref>

In addition, there are other forms of immune response. For example, harmless exogenous factors (such as pollen and food components) can trigger [[allergy]]; latex and metals are also known allergens.
A transplanted tissue (for example, blood) or organ can cause [[graft-versus-host disease]]. A type of immune reactivity known as [[Rh disease]] can be observed in pregnant women. These special forms of immune response are classified as [[hypersensitivity]]. Another special form of immune response is [[CD4+ T cells and antitumor immunity|antitumor immunity]].

In general, there are two branches of the immune response, the [[Innate immune system|'''innate''']] and the [[Adaptive immune system|'''adaptive''']], which work together to protect against pathogens. Both branches engage '''[[humoral]]''' and [[cell-mediated immunity|'''cellular''']] components.

The innate branch—the body's first reaction to an invader—is known to be a non-specific and quick response to any sort of pathogen . Components of the innate immune response include physical barriers like the skin and mucous membranes, immune cells such as [[neutrophil]]s, [[macrophage]]s, and [[monocyte]]s, and soluble factors including [[cytokine]]s and [[Complement system|complement]].<ref name=":2" /> On the other hand, the adaptive branch is the body's immune response which is catered against specific [[antigen]]s and thus, it takes longer to activate the components involved. The adaptive branch include cells such as [[dendritic cell]]s, [[T cell]], and [[B cell]]s as well as [[Antibody|antibodies]]—also known as immunoglobulins—which directly interact with antigen and are a very important component for a strong response against an invader.<ref name=":1" />

The first contact that an organism has with a particular antigen will result in the production of effector T and B cells which are activated cells that defend against the pathogen. The production of these effector cells as a result of the first-time exposure is called a '''primary''' immune response. [[Memory T cell|Memory T]] and [[memory B cell]]s are also produced in the case that the same pathogen enters the organism again. If the organism does happen to become re-exposed to the same pathogen, a '''secondary''' immune response will kick in and the immune system will be able to respond in both a fast and strong manner because of the memory cells from the first exposure.<ref>{{Cite web|url=https://www.britannica.com/science/immune-system|title=Immune system – Evolution of the immune system|website=Encyclopedia Britannica|language=en|access-date=2020-03-09}}</ref> [[Vaccine]]s introduce a weakened, killed, or fragmented microorganism in order to evoke a primary immune response. This is so that in the case that an exposure to the real pathogen occurs, the body can rely on the secondary immune response to quickly defend against it.<ref>{{Cite web|url=https://www.britannica.com/science/vaccine|title=vaccine {{!}} Definition, Types, History, & Facts|website=Encyclopedia Britannica|language=en|access-date=2020-03-09}}</ref>