Superantigen

A superantigen is a type of antigen that activates a very large proportion of T cells, regardless of their antigen specificity. Unlike conventional antigens, which require specific processing and presentation by antigen-presenting cells to T cell receptors (TCRs), superantigens can bind directly to the outer surfaces of both antigen-presenting cells and T cells. This interaction bypasses the normal antigen recognition pathway.

Superantigens are typically bacterial or viral proteins. They bind to the Vβ region of the T cell receptor and simultaneously to the major histocompatibility complex (MHC) class II molecules on antigen-presenting cells. This cross-linking bridges the T cell and the antigen-presenting cell, leading to the activation of a large number of T cells, often up to 20% of the total T cell population. This widespread activation can result in a massive release of cytokines, a phenomenon known as a cytokine storm.

The consequences of this hyperactivation can be severe and include symptoms such as fever, rash, shock, and organ failure. Some well-known examples of superantigens are produced by bacteria like Staphylococcus aureus (e.g., toxic shock syndrome toxin-1) and Streptococcus pyogenes. Viral superantigens have also been identified. The ability of superantigens to induce such a potent and non-specific immune response makes them significant contributors to certain infectious diseases and autoimmune conditions. Research into superantigens continues to provide insights into T cell activation mechanisms and the pathogenesis of immune-mediated disorders.