Superantigen

Superantigens (SAgs) are a group of virulent toxinsthat indiscriminately activate T-cellsof the immune system causing system-wide inflammationand other serious, potentially fatal symptoms. They are not quite the same as antigens, though they almost all have antigenic properties, but rather receive their name from their powers to induce the production of antibodies.

Symptoms

Characteristic symptoms of superantigen-mediated diseases include:

• fever
• mucusprduction
• diarrhoea
• vomiting
• shockleading to death

Chronic infection can cause autoimmune diseasesand glomerulonephritis.

Pathophysiology

Superantigens are secreted as exotoxinsby bacteria, alternatively viruseshijack our own molecular machinery to generate endotoxinforms of superantigens. They are mainly associated with species of Streptococcus and Staphylococcus infections, and are the contributing cause of toxic shock syndrome. Superantigens are also the suspected cause of numerous diseases displaying characteristic symptoms with unknown causes.

Rather than typical presentation by major histocompatibility complextype II molecules (MHC II) of antigen-presenting cellsto T-cell receptors(TCRs) inside specialised clefts, superantigens bind externally to the Vβ domain of the TCR and to the complementary chain of MHC II, causing inappropriate, antigen-independent T-cell activation. In a typical infection, 0.01% of the body's T-cells are activated; superantigen-mediated infections commonly activate 5% and can reach levels of up to 25% T-cell activation. These T-cells are of all populations (helper T cells, cytotoxic T cells, suppressor T cells, and as-yet-unidentified T-cell populations), and leads to a mass activation of multiple, often contradictory, chemical mediators that contribute to the general unwellness of an individual.

Research into superantigen treatment focuses on the use of polyspecific immunologlobulin G, antagonistic peptides, and toxoidvaccines. There is concern that bacterial superantigens may be mass-produced and used as bioweapons (Staphylococcus aureusB enterotoxin, for example - [1]).

Interestingly, superantigens have been shown to prevent and heal autoimmune disorders in animal experiments if the timing of administration is "just right".

Clinical notes

Diseases associated with superantigen production

• Food poisoning(Staphylococcus and Staphlycoccus)
• Toxic shock syndrome(Staphylococcus)
• Wegener's granulomatosis(Staphylococcus)
• Scarlet fever(Streptococcus)
• Yersinia pseudotuberculosis
• Mycoplasma arthriditis

Diseases in which superantigen production is suspected

• Kawasaki disease
• Allergicsinusitis
• Cytomegalovirus(with HIV)
• Epstein-Barr Virus(with HIV)
• Type I diabetes mellitus
• vasculitisand other unexplained inflammatory diseases

External links

• Superantigen Web Databaseat Birbeck University
• List of Superantigen Proteinsfrom UniProt

This article is licensed under the GNU Free Documentation License.
It uses material from the http://en.wikipedia.org/wiki/Superantigen Wikipedia article Superantigen.