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:4/17/2014)... German . ... demanded of him, he can expect his premises to be ... of the consequences is enough to make restaurant owners pay ... lay their eggs in other birds, nests. If the host ... their revenge by destroying the entire nest. Consequently, it is ...
(Date:4/17/2014)... in many serious conditions such as heart disease, epilepsy ... drug therapies. Unfortunately, there is still much scientists do ... fresh and unexpected insight into the structure of sodium ... molecules - which are responsible for ,fine-tuning, the activity ... most recent edition of the Journal of Biological ...
(Date:4/17/2014)... genetic information of DNA is used to manufacture ... different functions in living organisms. Messenger RNA (mRNA) ... by relating the genetic information of DNA to ... , By examining the different types and amounts ... a given time, researchers can determine which specific ...
Breaking Biology News(10 mins):Fear of the cuckoo mafia 2Fear of the cuckoo mafia 3Structure of sodium channels different than previously believed 2Rapid and accurate mRNA detection in plant tissues 2
... position paper by researchers at the European Centre for ... Peninsula College of Medicine and Dentistry) and the University of ... virtual natural environments and concluded that the development of accurate ... interact with nature because of infirmity or other limitations: ...
... 2011 A new study from University of Miami ... Chris Langdon, Remy Okazaki and Nancy Muehllehner and colleagues ... Max-Planck Institute for Marine Microbiology in Germany concludes that ... severely reduce the diversity and resilience of coral reef ...
... researcher Elias Tomaras says the idea came to him while ... "If you watch sprinters, short distance speed skaters or cyclists ... two hours, including several brief bouts of high intensity exercise. ... it might be pretty tiring." Many coaches and physiologists ...
Cached Biology News:Virtual natural environments and benefits to health 2Virtual natural environments and benefits to health 3Virtual natural environments and benefits to health 4Tiny bubbles signal severe impacts to coral reefs worldwide 2When it comes to warm-up, less is more 2
Other biology definitionOther Tags