Superantigen

Superantigen

Definition:
They are bacterial toxins or viral proteins that have the ability to bind to both MHC class II and TCR β chain outside the binding cleft.

Characters:

• They do not need to be processed.
• Able to activate all T cells irrespective of their antigen specificity.
• They interact with MHC molecules outside the peptide binding groove.
• Also bind with TCR β chain irrespective of antigen specificity.

Its effect:

• Polyclonal activation of T cells.
• They stimulate the release of abnormal large amounts of cytokines especially TNF.
• It can lead to shock.

Examples:

• Staphylococcal enterotoxin.
• Staphylococcal toxic shock syndrome toxins (TSST).
• Staphylococcal exfoliative toxin.
• Streptococcal pyrogenic exotoxins.