An antigen is a substance that is capable of inducing a specific immune response in the host into which it is introduced. The immune response is mediated via an immunoglobulin (protein) molecule, called an antibody, which is formed by B-lymphocytes and T-helper cells that are the basic ingredients of the host's immune system. "Antibody" is the generic name for any immunoglobulin thus produced, no matter how this occurs. Humans can produce many specific antibodies. This may be an active process by a healthy host in response to the challenge of exposure to a foreign antigen transmitted via the placenta or in maternal milk from mother to offspring, or it may be artificially induced by immunization with live attenuated organisms, killed organisms, or a protein derivative.
An antigen is an organic compound—a protein, polysaccharide or glycolipid. Sometimes it is an entire organ or tissue that has been transplanted into the host, which rejects it and attempts to destroy it. An antibody has the capacity to bind specifically to the (foreign) antigen and thereby neutralize it so it can be destroyed by the host's phagocytes.
The antibody is the basic ingredient of the host's defenses against infection. By measuring the concentration of specific antibodies in individuals and populations it is possible to determine levels of susceptibility and resistance to infection by specific pathogens. At the population level, this is called "sero-epidemiology."
An antigen is produced by living organisms, which evolve over generations and can therefore undergo subtle changes in protein composition, a process known as "antigen drift." A more sudden evolutionary change can lead to an abrupt change in protein structure, known as "antigen shift." Antigen drift renders an antibody less effective, and antigen shift makes an antibody ineffective in combating an antigen to which the host was immunized by exposure to the previous form of the antigen. Antigen drift and antigen shift account for recurrences of infection with viruses, such as those of the common cold and influenza.
John M. Last
(see also: Epidemiology; Immunizations )
"Antibody, Antigen." Encyclopedia of Public Health. . Encyclopedia.com. (February 19, 2019). https://www.encyclopedia.com/education/encyclopedias-almanacs-transcripts-and-maps/antibody-antigen
"Antibody, Antigen." Encyclopedia of Public Health. . Retrieved February 19, 2019 from Encyclopedia.com: https://www.encyclopedia.com/education/encyclopedias-almanacs-transcripts-and-maps/antibody-antigen
Encyclopedia.com gives you the ability to cite reference entries and articles according to common styles from the Modern Language Association (MLA), The Chicago Manual of Style, and the American Psychological Association (APA).
Within the “Cite this article” tool, pick a style to see how all available information looks when formatted according to that style. Then, copy and paste the text into your bibliography or works cited list.
Because each style has its own formatting nuances that evolve over time and not all information is available for every reference entry or article, Encyclopedia.com cannot guarantee each citation it generates. Therefore, it’s best to use Encyclopedia.com citations as a starting point before checking the style against your school or publication’s requirements and the most-recent information available at these sites:
Modern Language Association
The Chicago Manual of Style
American Psychological Association
- Most online reference entries and articles do not have page numbers. Therefore, that information is unavailable for most Encyclopedia.com content. However, the date of retrieval is often important. Refer to each style’s convention regarding the best way to format page numbers and retrieval dates.
- In addition to the MLA, Chicago, and APA styles, your school, university, publication, or institution may have its own requirements for citations. Therefore, be sure to refer to those guidelines when editing your bibliography or works cited list.