Staphylococcal toxic shock syndrome toxin-1 (TSST-1) acts as a superantigen. Its unique mechanism of T-cell activation, compared to conventional antigens, is:
- A It requires processing and presentation by MHC class I molecules to CD8+ T cells
- B It cross-links MHC class II on APCs with TCR Vβ regions outside the conventional antigen-binding groove, activating up to 20% of T cells simultaneously ✓
- C It directly ligates CD28 co-stimulatory receptor, bypassing TCR signaling
- D It activates only NK cells and gamma-delta T cells
Correct answer: B. It cross-links MHC class II on APCs with TCR Vβ regions outside the conventional antigen-binding groove, activating up to 20% of T cells simultaneously
Explanation
Superantigens such as TSST-1 bypass normal MHC-restricted antigen processing. They bind simultaneously to the alpha-1 domain of MHC class II (outside the peptide groove) and to the variable beta (Vβ) chain of the TCR, irrespective of conventional specificity. This cross-linking activates all T cells bearing particular Vβ families — up to 20% of the T-cell repertoire — causing a cytokine storm (TNF-α, IL-1, IL-6, IFN-γ) that manifests as toxic shock.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.