Staphylococcus aureus producing toxic shock syndrome toxin-1 (TSST-1) causes fever, rash, and multi-organ dysfunction. TSST-1 acts as a superantigen. Which immunological mechanism explains its ability to cause massive cytokine release?

• A It activates toll-like receptor 4 on macrophages like endotoxin
• B It binds IgE on mast cells triggering degranulation
• C It activates the alternative complement pathway leading to C5a release
• D It cross-links MHC class II outside the peptide groove with specific Vβ TCR regions, activating up to 20% of all T cells ✓

Explanation

Superantigens like TSST-1 bind simultaneously to MHC class II molecules (outside the antigen-binding groove) and to the Vβ chain of T-cell receptors in a non-antigen-specific manner, bypassing conventional antigen processing. This activates all T cells bearing a particular Vβ segment — up to 20% of the total T-cell pool — producing massive cytokine storm (IL-1, IL-2, TNF-α, IFN-γ). This dwarfs antigen-specific responses where only 1 in 10,000 T cells is activated. TSST-1 does not activate TLR4, IgE, or complement.

Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.