A precipitin is an antibody which can precipitate out of a solution upon antigen binding.[1]
Precipitin reaction
editThe precipitin reaction provided the first quantitative assay for antibody. The precipitin reaction is based upon the interaction of antigen 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 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 epitopes. This allows for the formation of large antigen:antibody complexes.
Medical diagnosis using precipitin tests
edit- 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.[2] For example, precipitin tests can be used to detect antigens of infectious bronchitis caused by the infectious bronchitis virus (IBV).[2]
- Allergy testing
Precipitin assays are used in allergy testing to identify allergen-specific antibodies (IgE) in patient serum samples.[3] 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.[3]
References
edit- ^ Heidelberger, Michael; Kendall, Forrest E. (30 November 1929). "A Quantitative Study of the Precipitin Reaction Between Type III Pneumococcus Polysaccharide and Purified Homologous Antibody". Journal of Experimental Medicine. 50 (6): 809–823. doi:10.1084/jem.50.6.809. ISSN 1540-9538. PMC 2131658. PMID 19869667.
- ^ a b Witter, Richard L. (1962). "The Diagnosis of Infectious Bronchitis of Chickens by the Agar Gel Precipitin Test". Avian Diseases. 6 (4): 478–492. doi:10.2307/1587924. ISSN 0005-2086. JSTOR 1587924.
- ^ a b Lau, Kevin S. K.; Yeung, Chantane; Carlsten, Chris (2020-09-03). "Stability of serum precipitins to Aspergillus fumigatus for the diagnosis of allergic bronchopulmonary aspergillosis". Allergy, Asthma & Clinical Immunology. 16 (1): 78. doi:10.1186/s13223-020-00476-4. ISSN 1710-1492. PMC 7491339. PMID 32944032.
External links
edit- Precipitins at the U.S. National Library of Medicine Medical Subject Headings (MeSH)
- Precipitin+tests at the U.S. National Library of Medicine Medical Subject Headings (MeSH)