## Toxic Shock Syndrome Toxin-1 (TSST-1) **Key Point:** TSST-1 is the primary exotoxin responsible for toxic shock syndrome (TSS) in S. aureus. It functions as a superantigen, bypassing normal antigen processing and causing massive T-cell activation and cytokine release. ### Superantigen Mechanism **Mnemonic:** SAG = **S**uperantigen = **A**ntigen-presenting cell + **G**erm-line T-cell receptor TSST-1 and other S. aureus superantigens: 1. Bind directly to MHC class II molecules on antigen-presenting cells 2. Bind to the variable region of the T-cell receptor (TCR Vβ chain) 3. Bypass normal peptide processing and presentation 4. Activate 5–30% of T cells (vs. 0.01% for conventional antigens) 5. Trigger massive release of IL-2, TNF-α, and IFN-γ 6. Lead to systemic inflammatory response, shock, and multi-organ failure ### S. aureus Superantigens | Toxin | Type | TSS Association | Notes | |---|---|---|---| | **TSST-1** | Exotoxin | Primary cause | Found in ~50% of TSS cases; phage-encoded | | **Enterotoxin A (SEA)** | Exotoxin | Secondary cause | Food poisoning + TSS | | **Enterotoxin B (SEB)** | Exotoxin | Secondary cause | Food poisoning + TSS | | **Enterotoxin C (SEC)** | Exotoxin | Secondary cause | Food poisoning + TSS | | **PVL** | Two-component toxin | Not superantigen | Causes leukocyte lysis | | **Alpha-hemolysin** | Pore-forming toxin | Not superantigen | Non-specific cell lysis | **High-Yield:** TSST-1 is the MOST COMMON cause of menstrual TSS (associated with tampon use). Enterotoxins are more common in food poisoning. **Clinical Pearl:** TSS can occur with non-invasive S. aureus infection (e.g., skin/soft tissue or vaginal colonization) because the toxin is released locally and absorbed systemically, causing systemic effects without bacteremia.
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