What are superantigens?
A superantigen belongs to the group of antigens. These antigens are structures of carbohydrates, fats, proteins or combinations thereof that can be produced by bacteria or viruses. The antigens enable the human body’s immune system to initiate an immune response by binding to an antibody. Unlike normal antigens, superantigens are not dependent on an intermediate stage of the immune response. Superantigens can therefore immediately trigger a very strong, unspecific and excessive immune response, such as Toxic Shock Syndrome (TSS).
What does a superantigen do?
The effect of a superantigen can be partially compared to the effect of normal antigens. In both cases the immune system is activated and responds with an immune response. While normal antigens induce a controlled immune reaction, which usually results in an adequate fight against the pathogen, a superantigen leads to a massive activation of immune cells, which can lead to a circulatory failure via mediators.
The massive effect of the superantigens is due to the fact that, compared to normal antigens, they are not taken up by so-called antigen-presenting cells and split into small fragments. Rather, they have a very high affinity to several receptors on the surface of immune cells such as the T-lymphocytes, thus bypassing a regulatory step of the immune system. A superantigen can also bind several receptors at once, which further enhances its effect.
This activates up to twenty times the number of immune cells compared to normal immune responses. However, as with any process in the body, an increased response of immune cells can also cause damage with the strong release of mediators or cytokines such as interleukins. Besides its effect as a superantigen, it can also trigger an adequate immune response as a normal antigen.
Structure of a superantigen
Superantigens belong to the group of globular proteins. This means that they have several domains that fold in the same way each time the protein is produced and perform specific tasks. In the case of superantigens, there are four domains with different functions such as binding of receptors and regulation of the activity of a receptor.
On the one hand, a receptor can be bound on the antigen-presenting cells. On the other hand, the so-called T cell receptor is bound on T lymphocytes. After binding of the two cells, the superantigen releases the inflammation mediators.
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