"Superantigens" cause damage by which mechanism?

• A. Molecular mimicry
• B. Polyclonal T cell activation
• C. Lysing white blood cells and platelets
• D. Lysing red blood cells

Answer: (B)

Superantigens trigger widespread, nonspecific T cell activation. They bind outside the normal peptide groove by attaching to MHC class II on antigen-presenting cells and to the variable region of the T cell receptor beta chain, effectively cross-linking these two cells without antigen processing. This bypasses specific antigen recognition and activates a large fraction of T cells, causing a massive release of cytokines (like IL-2, IFN-γ, TNF-α, IL-1). The resulting cytokine storm drives fever, shock, and tissue damage seen in diseases such as toxic shock syndrome. This differs from molecular mimicry, which involves autoimmunity due to cross-reactive antigens, and from direct lysis of cells by toxins such as leukocidins, platelets, or red blood cell–lysing agents.