View source for Immunology

'''Immunology''' is a broad branch of [[biomedical science|biomedical]] [[science]] that covers the study of all aspects of the [[immune system]] in all [[organism]]s.<ref>[http://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=imm.TOC&depth=2 Janeway's Immunobiology textbook] Searchable free online version at the [[National Center for Biotechnology Information]]</ref> It deals with the [[physiology|physiological]] functioning of the immune system in states of both health and disease; malfunctions of the immune system in immunological disorders ([[autoimmune diseases]], [[hypersensitivity|hypersensitivities]], [[immune deficiency]], [[transplant rejection]]); the physical, chemical and physiological characteristics of the components of the immune system [[in vitro]], [[in situ]], and [[in vivo]]. Immunology has applications in several disciplines of science, and as such is further divided.

==Histological examination of the immune system==
Even before the concept of [[immunity (medical)|immunity]] (from ''immunis'', [[Latin]] for "exempt") was developed, numerous early physicians characterized organs that would later prove to be part of the immune system. The key primary lymphoid organs of the immune system are like [[thymus]] and [[bone marrow]],  and secondary lymphatic tissues such as [[spleen]], [[tonsil]]s, [[lymphatic system|lymph vessels]], [[lymph node]]s, [[adenoid]]s, and [[skin]]. When health conditions warrant, immune system organs including the thymus, spleen, portions of bone marrow, lymph nodes and secondary lymphatic tissues can be [[surgery|surgically]] excised for examination while patients are still alive.

Many components of the immune system are actually [[cell (biology)|cell]]ular in nature and not associated with any specific organ but rather are embedded or circulating in various [[tissue (anatomy)|tissues]] located throughout the body.

==Classical immunology==
Classical immunology ties in with the fields of [[epidemiology]] and [[medicine]]. It studies the relationship between the body systems, [[pathogen]]s, and immunity. The earliest written mention of immunity can be traced back to the [[Pandemic|plague]] of [[Athens]] in 430 BCE. [[Thucydides]] noted that people who had recovered from a previous bout of the disease could [[nurse]] the sick without contracting the illness a second time. Many other ancient societies have references to this phenomenon, but it was not until the 19th and 20th centuries before the concept developed into scientific theory.

The study of the molecular and cellular components that comprise the immune system, including their function and interaction, is the central science of immunology. The immune system has been divided into a more primitive [[innate immunity|innate immune system]], and [[adaptive immunity|acquired or adaptive immune system]] of vertebrates, the latter of which is further divided into [[humoral immunity|humoral]] and [[cell-mediated immunity|cellular components]]. 

The humoral (antibody) response is defined as the interaction between [[antibody|antibodies]] and [[antigen]]s. Antibodies are specific proteins released from a certain class of immune cells (B lymphocytes).  Antigens are defined as anything that elicits generation of antibodies, hence they are '''Anti'''body '''Gen'''erators.  Immunology itself rests on an understanding of the properties of these two biological entities. However, equally important is the cellular response, which can not only kill infected cells in its own right, but is also crucial in controlling the antibody response. Put simply, both systems are highly interdependent.

In the 21st century, immunology has broadened its horizons with much research being performed in the more specialized niches of immunology. This includes the immunological function of cells, organs and systems not normally associated with the immune system, as well as the function of the immune system outside classical models of immunity (Yemeserach 2010).

==Clinical immunology== <!--Clinical immunology redirects here-->
Clinical immunology is the study of [[disease]]s caused by disorders of the immune system (failure, aberrant action, and malignant growth of the cellular elements of the system). It also involves diseases of other systems, where immune reactions play a part in the pathology and clinical features. 

The diseases caused by disorders of the immune system fall into two broad categories: [[immunodeficiency]], in which parts of the immune system fail to provide an adequate response (examples include [[chronic granulomatous disease]]), and [[autoimmunity]], in which the immune system attacks its own host's body (examples include [[systemic lupus erythematosus]], [[rheumatoid arthritis]], [[Hashimoto's disease]] and [[myasthenia gravis]]). Other immune system disorders include different [[hypersensitivity|hypersensitivities]], in which the system responds inappropriately to harmless compounds ([[asthma]] and other [[allergy|allergies]]) or responds too intensely.

The most well-known disease that affects the immune system itself is [[Acquired Immunodeficiency Syndrome|AIDS]], caused by [[HIV]]. AIDS is an immunodeficiency characterized by the lack of CD4+ ("helper") [[T cells]] and [[macrophages]], which are destroyed by HIV.

Clinical immunologists also study ways to prevent [[transplant rejection]], in which the immune system attempts to destroy [[allograft]]s or [[xenograft]]s.

==Developmental immunology==
The body’s capability to react to antigen depends on a person's age, antigen type, maternal factors and the area where the antigen is presented.<ref>Goldsby RA, Kindt TK, Osborne BA and Kuby J (2003) '''Immunology''', 5th Edition, W.H. Freeman and Company, New York, New York, ISBN 0-7167-4947-5</ref>  [[Neonate]]s are said to be in a state of physiological immunodeficiency, because both their innate and adaptive immunological responses are greatly suppressed.  Once born, a child’s immune system responds favorably to protein antigens while not as well to glycoproteins and polysaccharies. In fact, many of the infections acquired by neonates are caused by low virulence organisms like [[Staphylococcus]] and [[Pseudomonas]].  In neonates, opsonic activity and the ability to activate the [[complement cascade]] is very limited.  For example, the mean level of C3 in a newborn is approximately 65% of that found in the adult. Phagocytic activity is also greatly impaired in newborns. This is due to lower opsonic activity, as well as diminished up-regulation of [[integrin]] and [[selectin]] receptors, which limit the ability of neutrophils to interact with adhesion molecules in the endothelium. Their monocytes are slow and have a reduced ATP production, which also limits the newborns phagocitic activity.  Although, the number of total lymphocytes is significantly higher than in adults, the cellular and humoral immunity is also impaired.  Antigen presenting cells in newborns have a reduced capability to activate T cells.  Also, T cells of a newborn proliferate poorly and produce very small amounts of [[cytokine]]s like IL-2, IL-4, IL-5, IL-12, and IFN-g which limits their capacity to activate the humoral response as well as the phagocitic activity of macrophage.  B cells develop early in gestation but are not fully active.<ref name= Jaspan>Jaspan Heather, S.D Lawn; et al. "The maturing immune system: implications for development and testing HIV-1 vaccines for children and adolescents" AIDS21 Mar. 2006, Vol 20 p.p 483-494.</ref>
[[File:Monocyte.png|thumb|Monocytes: An Artist's Impression]]

Maternal factors also play a role in the body’s immune response.  At birth most of the immunoglobulin is present is maternal IgG.  Because IgM, IgD, IgE and IgA don’t cross the placenta, they are almost undetectable at birth.  Although some IgA is provided in breast milk.  These passively acquired antibodies can protect the newborn up to 18 months, but their response is usually short-live and of low affinity.<ref name= Jaspan/>  These antibodies can also produce a negative response.  If a child is exposed to the antibody for a particular antigen before being exposed to the antigen itself then the child will produce a dampened response. [[Passive immunity|Passively acquired maternal antibodies]] can suppress the antibody response to active immunization. Similarly the response of T-cells to vaccination differs in children compared to adults, and vaccines that induce Th1 responses in adults do not readily elicit these same responses in neonates.<ref name= Jaspan/> By 6-9 months after birth, a child’s immune system begins to respond more strongly to glycoproteins.  Not until 12-24 months of age is there a marked improvement in the body’s response to polysaccharides.  This can be the reason for the specific time frames found in vaccination schedules.<ref>Glezen WP. Maternal vaccines. Prim Care 2001(28):791.</ref><ref>Holt PG, Macaubas C, Cooper D, Nelson DJ, McWilliam AS. Th-1/Th-2 switch regulation in immune responses to inhaled antigens - role of dendritic cells in the aetiology of allergic respiratory disease. Dendritic Cells in Fundamental and Clinical Immunology 1997; (3) (417) 301–306.</ref>

During adolescence the human body undergoes several physical, physiological and immunological changes. These changes are started and mediated by different [[hormone]]s. Depending on the sex either [[testosterone]] or [[Estradiol|17-β-oestradiol]], act on male and female bodies accordingly, start acting at ages of 12 and 10 years.<ref>Sizonenko PC, Paunier L. Hormonal changes in puberty III: Correlation of plasma dehydroepiandrosterone, testosterone, FSH, and LH with stages of puberty and bone age in normal boys and girls and in patients with Addison's disease or hypogonadism or with premature or late adrenarche. J Clin Endocrinol Metab 1975; 41:894–904.</ref> There is evidence that these steroids act directly not only on the primary and secondary sexual characteristics, but also have an effect on the development and regulation of the immune system.<ref>Verthelyi D. Sex hormones as immunomodulators in health and disease. Int Immunopharmacol 2001; 1:983–993.</ref>  There is an increased risk in developing autoimmunity for pubescent and post pubescent females and males.<ref>Stimson WH. Oestrogen and human T lymphocytes: presence of specific receptors in the T-suppressor/cytotoxic subset. Scand J Immunol 1998; 28:345–350.</ref>  There is also some evidence that cell surface receptors on B cells and macrophages may detect sex hormones in the system.<ref>  Benten WPM, Stephan C, Wunderlich F. B cells express intracellular but not surface receptors for testosterone and estradiol. Steroids 2002; 67:647–654.</ref>  The female sex hormone 17-β-oestradiol has been shown to regulate the level of immunological response.<ref>Beagley K, Gockel CM. Regulation of innate and adaptive immunity by the female sex hormones oestradiol and progesterone. FEMS Immunol Med Microbiol 2003; 38:13–22.</ref>  Similarly, some male [[androgen]]s, like testosterone, seem to suppress the stress response to infection; but other androgens like DHEA have the opposite effect, as it increases the immune response instead of down playing it.<ref>Kanda N, Tamaki K. Estrogen enhances immunoglobulin production by human PBMCs. J Allergy Clin Immunol 1999; 103:282–288.</ref> As in females, the male sex hormones seem to have more control of the immune system during puberty and the time right after than in fully developed adults. Other than hormonal changes physical changes like the involution of the Thymus during puberty will also affect the immunological response of the subject or patient.<ref>McFarland RD, Douek DC, Koup RA, Picker LJ. Identification of a human recent thymic emigrant phenotype. Proc Natl Acad Sci USA 2000; 97:4215–4220.</ref>

==Immunotherapy==
{{Main|Immunotherapy}}
The use of immune system components to treat a disease or disorder is known as immunotherapy. Immunotherapy is most commonly used in the context of the treatment of [[cancer]]s together with [[chemotherapy]] ([[Medication|drug]]s) and [[radiotherapy]] ([[electromagnetic radiation|radiation]]). However, immunotherapy is also often used in the immunosuppressed (such as [[HIV]] patients) and people suffering from other immune deficiencies or autoimmune diseases.

==Diagnostic immunology==
{{Main|Diagnostic immunology}}
The specificity of the bond between antibody and antigen has made it an excellent tool in the detection of substances in a variety of diagnostic techniques. Antibodies specific for a desired [[antigen]] can be conjugated with a radiolabel, fluorescent label, or color-forming enzyme and are used as a "probe" to detect it. However, the similarity between some antigens can lead to false positives and other errors in such tests by antibodies cross-reacting with antigens that aren't exact matches.<ref>Miller JJ and Valdes R, Jr. Approaches to minimizing interference by cross-reacting molecules in immunoassays. Clin Chem 1991 37: 144-153.</ref>

==Evolutionary immunology==
Study of the immune system in extant and [[extinction|extinct]] species is capable of giving us a key understanding of the [[evolution]] of species and the immune system.

A development of complexity of the immune system can be seen from simple phagocytotic protection of single celled organisms, to circulating antimicrobial peptides in insects to lymphoid organs in vertebrates. Of course, like much of evolutionary observation, these physical properties are  often seen from the [[anthropocentric]] aspect.  It should be recognized that every organism living today has an immune system absolutely capable of protecting it from most forms of harm; those organisms that did not adapt their immune systems to external threats are no longer around to be observed.   

[[Insect]]s and other [[arthropod]]s, while not possessing true adaptive immunity, show highly evolved systems of innate immunity, and are additionally protected from external injury (and exposure to pathogens) by their [[chitin]]ous shells.

==Reproductive immunology==

{{Main|Reproductive immunology}}
This area of the immunology is devoted to the study of immunological aspects of the reproductive process including fetus acceptance. The term has also been used by fertility clinics to address fertility problems, recurrent miscarriages, premature deliveries, and dangerous complications such as pre-clampsia. 

==Immunologist==
{{Infobox Occupation
| name= Immunologist 
| image= 
| caption= 
| official_names= 
<!------------Details------------------->
| type= [[Profession]], [[Specialty (medicine)|Specialty]]
| activity_sector= [[Science]], [[Laboratory]], [[Medicine]]
| competencies= 
| formation= [[Doctor of Philosophy]], [[Medical Doctor]]
| employment_field= [[Hospital]]s, [[Clinic]]s, [[Academia]]
| related_occupation= [[Physician]], [[Research scientist]]
| average_salary= {{profit}} USD $74,000 - $132,000 (Ph.D.)<ref name=Profession/> {{profit}} $50,000- >$200,000 (M.D.)<ref>{{cite web |url=http://www.aboutbioscience.org/immunologist.html |title=Immunologist &#124; Bioscience Careers |format= |work= |accessdate=2009-09-10}}</ref>  
}}

According to the [[American Academy of Allergy, Asthma, and Immunology]] (AAAAI), "an immunologist is a [[research scientist]] who investigates the immune system of vertebrates (including the human immune system). Immunologists include research scientists ([[Ph.D.]]) who work in laboratories. Immunologists also include [[physicians]] who, for example, treat patients with immune system disorders. Some immunologists are physician-scientists who combine laboratory research with patient care."<ref name=Profession>{{cite web |url=http://science.education.nih.gov/LifeWorks.nsf/Alphabetical+List/Immunologist |title=Office of Science Education - LifeWorks - Immunologist |format= |work= |accessdate=2009-09-10}}</ref>

==See also==
* [[Outline of immunology]]
* [[List of immunologists]]
* [[History of immunology]]
* [[Osteoimmunology]]

== References ==
{{Reflist}}

== External links ==
{{WVD}}
* [http://www.aaaai.org/ American Academy of Allergy, Asthma & Immunology] 
* [http://arjournals.annualreviews.org/loi/immunol Annual Review of Immunology (journal)] 
* [http://www.biomedcentral.com/bmcimmunol/ BMC: Immunology]- [[BioMed Central]]:Immunology is an [[open access journal]] publishing original peer-reviewed research articles. 
* [http://www.nature.com/nri/index.html  journal home Nature Reviews Immunology]
* [http://www.immport.org The Immunology Database and Analysis Portal] - an NIAID-funded database resource of reference and experiment data covering the entire immunology domain
* [https://www.researchgate.net/group/Immunology  Current discussions on Immunology in a scientific community]

{{Medicine}}
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