Superantigen

Superantigens (SAG) are a complex of toxins with antigenic properties that are among the most potent activators of human T lymphocytes. Well known are bacterial and viral superantigens. Especially gram-positive bacteria are important producers of superantigens, here especially staphylococci and streptococci. Known superantigens are the erythrogenic scarlet toxins (see scarlet fever below) of the beta-hemolytic streptococci of the Lancefield group.

Among the gram-negative microorganisms, the toxins MAM and YPM of Mycoplasma arthritidis and Yersinia pseudotuberculosis are known as superantigens.

The Epstein-Barr-Virus (EBV) as well as HIV-1 (see below HIV infection) are also producers of superantigens.

• SAG lead to a stimulation of T cells by cross-linking of MHC II (histocompatibility II complex of antigen presenting cells APC) and T cell receptor (superantigens bind to monomorphic, i.e. conserved sequences of the hypervariable regions of the beta chains of T cell receptors - TCR V beta region) without the need for specific recognition of an antigen presented by the MHCII complex. Independent of the antigen specificity of the T lymphocytes, this leads to a fulminant and completely uncoordinated activation and release of cytokines and thus to an excessive inflammatory reaction of the organism (e.g. shock syndrome, toxic).
• SAG also act to a lesser extent than conventional antigens (see Antigen). Detection of IgE and IgG antibodies against SAG, whereby an IgE-mediated histamine release takes place (amplification of the inflammatory reaction).
• After superantigen-induced activation of the T cells, massive systemic lymphokine release occurs within a short time. Especially the cytokines TNF-alpha as well as the interleukins IL-1, 2, 6 and IFN-gamma. The abnormal release of lymphokines seems to be a cause of toxic shock syndrome and a number of other diseases.
• SAGs have an influence in some skin diseases, such as scarlet fever, atopic eczema, psoriasis vulgaris and mycosis fungoides.