Final answer:
An example of a superantigen is Staph enterotoxin, which binds to MHC class II molecules and stimulates a large number of T cells, leading to a cytokine storm and severe inflammatory responses.
Step-by-step explanation:
An example of a superantigen is the Staph enterotoxin. Superantigens have a unique binding mode to MHC class II molecules which allows them to activate a large number of T cells non-specifically. This is opposed to normal antigen presentation, where only T cells with a specific receptor for the presented antigen are activated. Superantigens bind outside of the antigen-binding cleft, bridging MHC II and the TCR (T cell receptor) ß chain without specific foreign epitope recognition.
The binding of superantigens to MHC class II molecules and TCRs leads to massive production and secretion of cytokines by CD4 T cells, often termed a 'cytokine storm,' causing an excessive inflammatory response. This can have serious, potentially fatal, implications such as shock and multi-organ failure. Unlike a controlled T cell response, superantigens elicit a massive and unregulated response that can be detrimental to the host.
Additional examples of bacterial superantigens include toxic shock syndrome toxin (TSST), streptococcal pyrogenic toxins, and streptococcal superantigen. Certain viruses such as the Epstein-Barr virus and cytomegalovirus are also known to produce superantigens.