A precipitin is an
antibody
An antibody (Ab) or immunoglobulin (Ig) is a large, Y-shaped protein belonging to the immunoglobulin superfamily which is used by the immune system to identify and neutralize antigens such as pathogenic bacteria, bacteria and viruses, includin ...
which can
precipitate
In an aqueous solution, precipitation is the "sedimentation of a solid material (a precipitate) from a liquid solution". The solid formed is called the precipitate. In case of an inorganic chemical reaction leading to precipitation, the chemic ...
out of a solution upon antigen binding.
Precipitin reaction
The precipitin reaction provided the first
quantitative
Quantitative may refer to:
* Quantitative research, scientific investigation of quantitative properties
* Quantitative analysis (disambiguation)
* Quantitative verse, a metrical system in poetry
* Statistics, also known as quantitative analysis
...
assay
An assay is an investigative (analytic) procedure in laboratory medicine, mining, pharmacology, environmental biology and molecular biology for qualitatively assessing or quantitatively measuring the presence, amount, or functional activity ...
for antibody. The precipitin reaction is based upon the interaction of
antigen
In immunology, an antigen (Ag) is a molecule, moiety, foreign particulate matter, or an allergen, such as pollen, that can bind to a specific antibody or T-cell receptor. The presence of antigens in the body may trigger an immune response.
...
with antibody leading to the production of
antigen-antibody complexes.
To produce a precipitin reaction, varying amounts of soluble antigen are added to a fixed amount of serum containing antibody. As the amount of antigen added:
* In the zone of antibody excess, each molecule of antigen is bound extensively by antibody and crosslinked to other molecules of antigen. The average size of antibody-antigen complex is small; cross-linking between antigen molecules by antibody is rare.
* In the zone of equivalence, the formation of precipitin complexes is optimal. Extensive lattices of antigen and antibody are formed by cross-linking.
* At high concentrations of antigen, the average size of antibody-antigen complexes is once again small because few antibody molecules are available to cross-link antigen molecules together.
The small, soluble immune complexes formed ''
in vivo
Studies that are ''in vivo'' (Latin for "within the living"; often not italicized in English) are those in which the effects of various biological entities are tested on whole, living organisms or cells, usually animals, including humans, an ...
'' in the zone of antigen excess can cause a variety of pathological syndromes.
Antibody can only precipitate antigenic substrates that are multivalent—that is, only antigens that have multiple antibody-binding sites
epitope
An epitope, also known as antigenic determinant, is the part of an antigen that is recognized by the immune system, specifically by antibodies, B cells, or T cells. The part of an antibody that binds to the epitope is called a paratope. Although e ...
s. This allows for the formation of large antigen:antibody complexes.
Medical diagnosis using precipitin tests
;Infectious disease diagnosis
Precipitin assays are commonly used in the diagnosis of infectious diseases caused by bacteria, viruses, fungi, and parasites. By detecting the presence of pathogen-specific antigens in patient samples, healthcare professionals can identify the causing agent of an infection and initiate appropriate treatment.
For example, precipitin tests can be used to detect antigens of infectious bronchitis caused by the
infectious bronchitis virus
Infectious bronchitis virus (IBV) is a species of virus from the genus ''Gammacoronavirus'' that infects birds. It causes avian infectious bronchitis, a highly infectious disease that affects the respiratory tract, gut, kidney and reproductive ...
(IBV).
;Allergy testing
Precipitin assays are used in allergy testing to identify allergen-specific antibodies (IgE) in patient serum samples.
By exposing the serum to a panel of common allergens, such as pollen, dust mites, pet dander, and food proteins, healthcare professionals can determine the specific allergens triggering an individual's allergic reactions.
References
External links
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* {{MeshName, Precipitin+tests
Biochemistry detection reactions
Immune system