Navigation Links
Antigen


An antigen is any molecule that is recognized by antibodies. Usually, an antigen is a protein or a polysaccharide, but it can be any type of molecule, even small molecules if coupled to a large carrier (haptens).


There are several kinds of antigens:

  • Immunogen - Any substance that provokes an immune response (provokes immunity) when introduced into the body. An immunogen is always a macromolecule (protein, polysaccharide). Its ability to provoke the immune response depends on its foreignness to the host, molecular size, chemical composition and heterogeneity (e.g. different amino acids in a protein).
  • Tolerogen - An antigen that invokes a specific immune unresponsiveness due to its molecular form . A tolerogen can become an immunogen if its molecular form is changed.
  • Allergen - An allergen is any substance that causes an allergic reaction. It can be eaten, inhaled, injected or comes into contact with skin.

Antigens are presented by a cell to its environment via a histocompatibility molecule. Depending on the antigen presented and the histocompatibility molecule used, several types of immune cells can leap into action.

We can also classify antigens according to where they come from:

  • Exogenous antigens

Exogenous antigens are antigens that have entered the body, e.g., by inhalation, ingestion, or injection. These antigens are taken up by endocytosis or phagocytosis into the antigen presenting cells (APCs), and degraded into fragments. The fragments are then presented on the surface of APCs by class II histocompatibility molecules to T helper cells (CD4+). Those that are specific for them, get activated, so they start to secrete cytokines. The cytokines then activate cytotoxic lymphocytes T (CTL), antibodies secreting lymphocytes B , macrophages and other cells.

  • Endogenous antigens

Endogenous antigens are antigens that have been generated within the cell, as a result of normal cell metabolism, or because of viral or intracellular bacterial infection. The fragments are then presented on the cell surface in the complex with class I histocompatibility molecules. If cytotoxic CD8+ T cells recognize them, they begin to secrete different toxins that cause the lysis or apoptosis of the infected cell. In order to keep the cytotoxic cells from killing cells just for presenting normal proteins, they run through a test cycle (negative control in the thymus) just after their production. Only those CTL that do not react to normal body protein fragments are allowed to enter the bloodstream.


'"/>


(Date:9/30/2014)... 2014  Spectra Automation, a trusted supplier ... and power generation industries, announced today the ... an easy-to-use and cost-effective data collection, analysis ... laboratories. Most upstream process ... systems. Accessing and consolidating data from these ...
(Date:9/29/2014)... Clostridium ramosum , coupled with a high-fat diet, may ... week in mBio , the online open-access journal of ... from the German Institute of Human Nutrition Potsdam-Rehbruecke in Nuthetal ... ramosum gained weight when fed a high-fat diet. Mice ... obese even when consuming a high-fat diet, and mice that ...
(Date:9/29/2014)... "human activities in this area of the world have contributed ... grown for use as a cooking oil and biofuel, while ... the most widely produced edible oil in the world, and ... soybean oil. , The environmental effects of such growth have ... crop, and the preferred method is fire. The clearing often ...
Breaking Biology News(10 mins):Spectra Automation Introduces RECONN Bioprocess Manager 2Gut bacteria promote obesity in mice 2
... food meal is never good for you, but washing that ... a new University of Guelph study. Researcher Marie-Soleil Beaudoin ... levels spike after eating a high-fat meal, but that the ... coffee jumping to levels similar to those of people ...
... leaves influence the sunlight reaching inner canopy leaves by changing ... physiology of leaves within the tree canopy is not constant, ... crown. This phenomenon is expected to have important consequences for ... A new study describes how the leaves in the outer ...
... ARBOR, Mich.Getting older doesn,t mean giving up muscle strength. ... loss that comes with age, but the Golden Years can be ... Michigan Health System. "Resistance exercise is a great ... people can function more readily in daily life," says Mark Peterson, ...
Cached Biology News:Got a craving for fast food? Skip the coffee, study says 2Older and stronger: Progressive resistance training can build muscle, increase strength as we age 2Older and stronger: Progressive resistance training can build muscle, increase strength as we age 3Older and stronger: Progressive resistance training can build muscle, increase strength as we age 4
Other biology definitionOther Tags