Immunity (medical)
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'''Immunity''' is a material term that describes a state of having sufficient biological defenses to avoid [[infection]], [[disease]], or other unwanted biological invasion. Immunity involves both specific and non-specific components. The non-specific components act either as barriers or as eliminators of wide range of pathogens irrespective of antigenic specificity. Other components of the [[immune system]] adapt themselves to each new disease encountered and are able to generate pathogen-specific immunity.
'''[[Adaptive immunity]]''' is often sub-divided into two major types depending on how the immunity was introduced. '''Naturally acquired immunity''' occurs through contact with a disease causing agent, when the contact was not deliberate, whereas '''artificially acquired immunity''' develops only through [[Artificial induction of immunity|deliberate actions]] such as vaccination. Both naturally and artificially acquired immunity can be further subdivided depending on wheather immunity is induced in the host or passively transferred from a immune host. '''Passive immunity''' is acquired through transfer of antibody or activated T-cells from a immune host, and is short lived, usually lasts only a few months, whereas '''active immunity''' is induced in the host itself by antigen, and lasts much longer, sometimes life-long. The diagram below summarizes these divisions of immunity.
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[[Image:Immunity.png||center|600x300px|]]
A further subdivision of adaptive immunity is characterized by the cells involved; [[humoral immunity]] is the aspect of immunity that is mediated by secreted antibodies, whereas the protection provided by [[cell mediated immunity]] involves T-lymphocytes alone. Humoral immunity is active when the organism generates its own antibodies, and passive when antibodies are transferred between individuals. Similarly, cell mediated immunity is active when the organisms’ own T-cells are stimulated and passive when T cells come from another organism.
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==History of theories of immunity==
[[Image:Cholera art.jpg|thumb|250px|right|A representation of the [[cholera]] [[epidemic]] of the nineteenth century.]]
The concept of immunity has intrigued mankind for thousands of years. The prehistoric view of disease was that it was caused by supernatural forces, and that illness was a form of [[Theurgy|theurgic]] punishment for “bad deeds” or “evil thoughts” visited upon the soul by the gods or by one’s enemies.<ref name= Rhodes>Lindquester, Gary J. (2006) [http://www.rhodes.edu/biology/glindquester/disimm/history.html Introduction to the History of disease.] Disease and Immunity, Rhodes College.</ref> Between the time of [[Hippocrates]] and the 19th century, when the foundations of the scientific method were laid, diseases were attributed to an alteration or imbalance in one of the [[four humors]] (blood, phlegm, yellow bile or black bile).<ref name=Silverstein>Silverstein, Arthur M. (1989) History of Immunology (Hardcover) Academic Press. Note: The first six pages of this text are available online at: ([http://www.amazon.com/gp/reader/012643770X Amazon.com easy reader])</ref> Also popular during this time was the [[miasma theory of disease|miasma theory]], which held that diseases such as [[cholera]] or the [[Black Plague]] were caused by a miasma, a noxious form of "bad air".<ref name= Rhodes/> If someone were exposed to the miasma, they could get the disease.
The modern word “immunity” derives from the [[latin]] ''immunis'', meaning exemption from military service, tax payments or other public services.<ref name= Gheradi/> The first written descriptions of the concept of immunity may have been made by the Athenian [[Thucydides]] who, in 430 BC, described that when the plague hit [[Athens]] ''“the sick and the dying were tended by the pitying care of those who had recovered, because they knew the course of the disease and were themselves free from apprehensions. '''For no one was ever attacked a second time, or not with a fatal result'''”''.<ref name= Gheradi>Gherardi E. [http://nfs.unipv.it/nfs/minf/dispense/immunology/immun.html The Concept of Immunity. History and Applications.] Immunology Course Medical School, University of Pavia.</ref> The term “immunes”, is also found in the epic poem “[[Pharsalia]]” written around 60 B.C. by the poet [[Marcus Annaeus Lucanus]] to describe a North African tribe’s resistance to [[snake venom]].<ref name=Silverstein/>
The first clinical description of immunity which arose from a specific disease causing organism is probably ''Kitab fi al-jadari wa-al-hasbah'' (''A Treatise on Smallpox and Measles'', translated 1848<ref>[http://www.answers.com/topic/al-razi A "al-Razi."] 2003 The Columbia Electronic Encyclopedia, Sixth Edition. Columbia University Press (from Answers.com, 2006.)</ref>) written by the [[Islamic]] physician [[Al-Razi]] in the 9th century. In the treatise, Al Razi describes the clinical presentation of smallpox and measles and goes on to indicate that that exposure to these specific agents confers lasting immunity (although he does not use this term).<ref name=Silverstein/> However, it was with [[Louis Pasteur]]’s [[Germ theory of disease]] that the fledgling science of [[immunology]] began to explain how bacteria caused disease, and how, following infection, the human body gained the ability to resist further insults.<ref name= Gheradi/>
[[Image:Tableau Louis Pasteur.jpg|thumb|left|200px|Louis Pasteur in his laboratory, 1885.]]
The birth of passive immunotherapy may have begun with [[Mithridates VI of Pontus]], who sought to harden himself against poison, and took daily sub-lethal doses of poison to build tolerance. Mithridates is also said to have fashioned a 'universal antidote' to protect him from all earthly poisons.<ref name=Silverstein/> For nearly 2000 years, poisons were thought to be the [[Proximate causation|proximate cause]] of disease, and a complicated mixture of ingredients, called [[Mithridate]], was used to cure poisoning during the [[Renaissance]].<ref name=Silverstein/> An updated version of this cure, [[Theriacum Andromachi]], was used well into the 19th century.<ref>{{note label|1728|1|^}}{{1728}} "[http://digicoll.library.wisc.edu/cgi-bin/HistSciTech/HistSciTech-idx?type=turn&entity=HistSciTech000900250210&isize=L Mithridate]".</ref>
In 1888 [[Emile Roux]] and [[Alexandre Yersin]] isolated [[diphtheria toxin]], and following the 1890 discovery by [[Emil Adolf von Behring|Behring]] and [[Shibasaburo Kitasato|Kitasato]] of antitoxin based immunity to [[diphtheria]] and [[tetanus]], the [[antitoxin]] became the first major success of modern therapeutic Immunology.<ref name=Silverstein/>
In [[Europe]], the induction of active immunity emerged in an attempt to contain [[smallpox]]. Immunization, however, had existed in various forms for at least a thousand years.<ref name= Gheradi/> The earliest use of immunization is unknown, however, around 1000 A.D., the [[Chinese people|Chinese]] began practicing a form of immunization by drying and inhaling powders derived from the crusts of smallpox lesions.<ref name= Gheradi/> Around the fifteenth century in [[India]], the [[Ottoman Empire]], and [[east Africa]], the practice of [[variolation]] (poking the skin with powdered material derived from smallpox crusts) became quite common.<ref name= Gheradi/> Variolation was introduced to the west in the early 18th century by [[Lady Mary Wortley Montagu]].<ref name= Gheradi/> In 1796, [[Edward Jenner]] introduced the far safer method of [[inoculation]] with the [[cowpox]] virus, a non-fatal virus that also induced immunity to smallpox. The success and general acceptance of Jenner's procedure would later drive the general nature of [[vaccination]] developed by Pasteur and others towards the end of the 19th century.<ref name=Silverstein/>
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==Passive immunity==
{{main|Passive immunity}}
Passive immunity is the transfer of active immunity, in the form of readymade antibodies, from one individual to another. Passive immunity can occur naturally, when maternal antibodies are transferred to the fetus through the placenta, and can also be induced artificially, when high levels of [[human]] (or [[horse]]) [[antibodies]] specific for a [[pathogen]] or [[toxin]] are transferred to non-[[immune system|immune]] individuals. Passive immunization is used when there is a high risk of infection and insufficient time for the body to develop its own immune response, or to reduce the symptoms of ongoing or [[immunosuppression|immunosuppressive]] diseases.<ref name=USC>[http://pathmicro.med.sc.edu/ghaffar/immunization.htm Microbiology and Immunology On-Line Textbook]: USC School of Medicine</ref> Passive immunity provides immediate protection, but the body does not develop memory, therefore the patient is at risk of being infected by the same pathogen later.<ref name=Janeway>{{cite book | last = Janeway | first = Charles | authorlink = Charles Janeway | coauthors = Paul Travers, Mark Walport, and Mark Shlomchik | title = Immunobiology; Fifth Edition | publisher = Garland Science | date = 2001 | location = New York and London| pages = | url = http://www.ncbi.nlm.nih.gov/books/bv.fcgi?call=bv.View..ShowTOC&rid=imm.TOC&depth=10| doi = | id = ISBN 0-8153-4101-6}}.</ref>
===Naturally acquired passive immunity===
Maternal passive immunity is a type of naturally acquired passive immunity, and refers to [[antibody]]-mediated immunity conveyed to a [[fetus]] by its mother during pregnancy. Maternal antibodies (MatAb) are passed through the [[placenta]] to the fetus by an [[FcRn]] receptor on placental cells. This occurs around the third month of [[gestation]].<ref name=Coico>Coico, R., Sunshine, G., and Benjamin, E. (2003). “Immunology: A Short Course.” Pg. 48.</ref> IgG is the only antibody [[Isotype (immunology)|isotype]] that can pass through the placenta.<ref name=Coico/> Passive immunity is also provided through the transfer of [[IgA]] antibodies found in [[breast milk]] that are transferred to the gut of the infant, protecting against bacterial infections, until the newborn can synthesize its own antibodies.<ref name=Janeway/>
[[Image:Antitoxin diphtheria.jpg|thumb|120px|right|One of the first bottles of [[diphtheria]] antitoxin produced (Dated 1895).]]
===Artificially acquired passive immunity===
''see also: [[artificial induction of immunity#Temporarily-induced immunity|Temporarily-induced immunity]]''
Artificially acquired passive immunity is a short-term immunization induced by the transfer of antibodies, which can be administered in several forms; as human or animal blood plasma, as pooled human immunoglobulin for intravenous ([[IVIG]]) or intramuscular (IG) use, and in the form of [[monoclonal antibodies]] (MAb). Passive transfer is used [[prophylactic]]ally in the case of [[immunodeficiency]] diseases, such as [[hypogammaglobulinemia]].<ref name= Keller>{{cite journal | author = Keller, Margaret A. and E. Richard Stiehm | title = Passive Immunity in Prevention and Treatment of Infectious Diseases | url=http://cmr.asm.org/cgi/content/full/13/4/602 | journal = Clinical Microbiology Reviews| volume = 13 | issue = 4 | pages = 602–614 | year = 2000 | pmid = 11023960 | doi = 10.1128/CMR.13.4.602-614.2000}}</ref> It is also used in the treatment of several types of acute infection, and to treat [[poison]]ing.<ref name=USC/> Immunity derived from passive immunization lasts for only a short period of time, and there is also a potential risk for [[hypersensitivity]] reactions, and [[serum sickness]], especially from [[gamma globulin]] of non-human origin.<ref name=Janeway/>
The artificial induction of passive immunity has been used for over a century to treat infectious disease, and prior to the advent of [[antibiotics]], was often the only specific treatment for certain infections. Immunoglobulin therapy continued to be a first line therapy in the treatment of severe [[respiratory disease]]s until the 1930’s, even after [[sulfonamide (medicine)|sulfonamide]] antibiotics were introduced.<ref name= Keller/>
===Passive transfer of cell-mediated immunity===
Passive or "adoptive transfer" of cell-mediated immunity, is conferred by the transfer of "sensitized" or activated T-cells from one individual into another. It is rarely used in humans because it requires [[histocompatibility|histocompatible]] (matched) donors, which are often difficult to find. In unmatched donors this type of transfer carries severe risks of [[graft versus host disease]].<ref name=USC/> It has, however, been used to treat certain diseases including some types of [[cancer]] and [[immunodeficiency]]. This type of transfer differs from a [[bone marrow transplant]], in which (undifferentiated) [[hematopoietic stem cell]]s are transferred.
==Active Immunity==
[[Image:Immune response.jpg|thumb|350px|The time course of an immune response. Due to the formation of immunological memory, reinfection at later time points leads to a rapid increase in antibody production and effector T cell activity. These later infections can be mild or even inapparent.]]
When [[B cells]] and [[T cells]] are activated by a pathogen, memory B-cells and T- cells develop. Throughout the lifetime of an animal these memory cells will “remember” each specific pathogen encountered, and are able to mount a strong response if the pathogen is detected again. This type of immunity is both ''active'' and ''adaptive'' because the body's immune system prepares itself for future challenges. Active immunity often involves both the cell-mediated and humoral aspects of immunity as well as input from the [[innate immune system]]. The ''innate system'' is present from birth and protects an individual from pathogens regardless of experiences, whereas [[adaptive immunity]] arises only after an infection or immunization and hence is "acquired" during life.
=== Naturally acquired active immunity===
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Naturally acquired active immunity occurs when a person is exposed to a live pathogen, and develops a primary [[immune response]], which leads to immunological memory.<ref name=USC/> This type of immunity is “natural” because it is not induced by man. Many disorders of immune system function can affect the formation of active immunity such as [[immunodeficiency]] (both acquired and congenital forms) and [[immunosuppression]].
=== Artificially acquired active immunity===
{{main|artificial induction of immunity|vaccination}}
Artificially acquired active immunity can be induced by a [[vaccine]], a substance that contains antigen. A vaccine stimulates a primary response against the antigen without causing symptoms of the disease.<ref name=USC/>The term vaccination was coined by [[Edward Jenner]] and adapted by [[Louis Pasteur]] for his pioneering work in vaccination. The method Pasteur used entailed treating the infectious agents for those diseases so they lost the ability to cause serious disease. Pasteur adopted the name vaccine as a generic term in honor of Jenner's discovery, which Pasteur's work built upon.[[Image:Poster for vaccination against smallpox.jpg|thumb|200px|Poster from before the 1979 eradication of smallpox, promoting vaccination.]]
In 1807, the [[Bavarians]] became the first group to require that their military recruits be vaccinated against smallpox, as the spread of smallpox was linked to combat.<ref name="NIH-Variolation">[[National Institutes of Health]] "Smallpox - A Great and Terrible Scourge" [http://www.nlm.nih.gov/exhibition/smallpox/sp_variolation.html Variolation]</ref> Subsequently the practice of vaccination would increase with the spread of war.
There are four types of traditional [[vaccine]]s:<ref>[http://www2.cdc.gov/nip/isd/ycts/mod1/courses/genrec/10300.asp?student_id= ''Immunization: You call the shots.''] The National Immunization Program at the Centers for Disease
Control and Prevention</ref>
* Inactivated vaccines are composed of micro-organisms that have been killed with chemicals and/or heat and are no longer infectious. Examples are vaccines against [[Influenza vaccine|flu]], [[cholera]], [[bubonic plague]], and [[hepatitis A]]. Most vaccines of this type are likely to require booster shots.
* Live, [[Attenuator (genetics)|attenuated]] vaccines are composed of micro-organisms that have been cultivated under conditions which disable their ability to induce disease. These responses are more durable and do not generally require booster shots. Examples include [[yellow fever]], [[measles]], [[rubella]], and [[mumps]].
* [[Toxoid]]s are inactivated toxic compounds from micro-organisms in cases where these (rather than the micro-organism itself) cause illness, used prior to an encounter with the toxiod. Examples of toxoid-based vaccines include [[tetanus]] and [[diphtheria]].
* [[Subunit]] -vaccines are composed of small fragments of disease causing organisms. A characteristic example is the subunit vaccine against [[Hepatitis B virus]].
Most vaccines are given by [[hypodermic]] injection as they are not absorbed reliably through the gut. Live attenuated [[Polio]] and some [[Typhoid]] and [[Cholera]] vaccines are given [[Mouth|oral]]ly in order to produce immunity based in the [[bowel]].
==See also==
*[[Antiserum]]
*[[Antivenin]]
*[[Immunology]]
*[[Inoculation]]
== References ==
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[[Category:Immune system]]
[[Category:Immunology]]
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