How does a superantigen activate the immune system?

A superantigen can activate the T-lymphocytes after binding to the T-cell receptor. In addition, superantigens can activate immune cells after binding of two different cells. Each domain of the superantigen has a task.

Like most globular proteins, superantigens have binding domains that help bind a structure on the surface of cells. Furthermore, they possess so-called regulatory domains, which can change the affinity and activity of the protein or target cell to a domain. Overall, an interaction of all domains of the superantigens leads to an activation of the immune cells.

Consequences of activation

After activation of immune cells, especially T lymphocytes, by binding of the T cell receptor by the superantigen, an excessive immune reaction occurs. Compared to a normal immune response, it can be increased by up to twenty times the highest normal immune response. This results in an activation of up to 20% of the T lymphocytes.

This leads to a massive release of so-called cytokines, which act systemically, i.e. in the entire organism. These cytokines also have a variety of mechanisms of action, which is why the symptoms of the affected person can be relatively complicated. In most cases, however, this leads to a failure of the circulation. There is also a connection between superantigens and diseases like

Diabetes mellitus,
Rheumatoid arthritis,
Multiple sclerosis and
Of endocarditis is discussed.

Examples of a superantigen

The superantigens are usually of bacterial or viral origin. The best known is probably the superantigen of the bacterium Staphylococcus aureus.This antigen is called Toxic shock syndrome toxin (TSST-1) and is responsible for toxic shock syndrome (TSS). This bacterium can also form a so-called exofoliative toxin, which is also considered a superantigen.

TSST-1 can also be produced by the bacterium Streptococcus pyogenes. The scarlet toxins Spe-A, Spe-B and Spe-C are also produced by this bacterium and are considered to be superantigens. Gram-negative bacteria can form the superantigens MAM and YPM. Other superantigens are SPEH, SPEJ or also SMEZ.