Navigation Links

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:7/29/2014)... As the climate warms and sea ice retreats, the ... season of increasingly open water which is predicted to ... of this century. Storms thus have the potential to ... a new and unpredictable element to the region. , A ... waves in the middle of the Arctic Ocean, and ...
(Date:7/29/2014)... a restaurant, don,t blame yourself; blame the menu. What ... want and more to do with a menu,s layout and ... over 300 diners, the Cornell study published this month in ... when it comes to what you order for dinner, two ... how you imagine it will taste. , First, any food ...
(Date:7/29/2014)... Scale plays a major role in locomotion. Swimming microorganisms, ... small inertial forces compared to the viscous forces exerted ... self-propulsion a major challenge. Now, scientists have found that ... is opposite to that induced by a viscoelastic fluid. ... by Franois Nadal from the Alternative Energies and ...
Breaking Biology News(10 mins):Huge waves measured for first time in Arctic Ocean 2Huge waves measured for first time in Arctic Ocean 3Menu secrets that can make you slim by design 2Optimum inertial self-propulsion design for snowman-like nanorobot 2
... Scripps Health announced today it has launched an innovative ... help determine the causes of idiopathic human diseases -- those ... or are unresponsive to standard treatments. The use of ... and treating rare medical cases. Whole genome sequencing provides ...
... identified and mapped the chemical structure of molecules used by ... growth of reef-building coral. Chemicals found on the surfaces ... coral, suggesting that competition with these macroalgae could be a ... of coral reefs. Seaweed growth on coral reefs ...
... difficult to measure accurately each nation,s contribution of carbon dioxide ... ground as coal, gas, and oil, and these fuels are ... generate the energy that is used to make products. In ... where they are consumed. A team led by Carnegie,s Steven ...
Cached Biology News:Scripps launches whole genome sequencing study to find root causes of idiopathic diseases 2Scripps launches whole genome sequencing study to find root causes of idiopathic diseases 3Study identifies molecules used by certain species of seaweed to harm corals 2Study identifies molecules used by certain species of seaweed to harm corals 3Study identifies molecules used by certain species of seaweed to harm corals 4Links in the chain: Global carbon emissions and consumption 2
Other biology definitionOther Tags