Educational resource · Not a medical device · Infectious diseases review in progress · Does not replace clinical judgement

Diagram — Exotoxins and superantigens — SeptiMap

distinguish the superantigen, which massively activates T cells, from A-B and pore-forming toxins, which act on a target cell. Educational resource, not a medical device.

Diagrams: mechanisms and principles

17 sourced diagrams · for medical students and practice

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Preclinical · clinical years

Exotoxins and superantigens

Objective: distinguish the superantigen, which massively activates T cells, from A-B and pore-forming toxins, which act on a target cell.

Step 6 / 6
Exotoxins and superantigens1. The bridge — The superantigen bridges the MHC II of the presenting cell and the Vβ region of the T-cell receptor, without antigen processing. 2. Massive activation — Up to 50% of T cells are activated, versus about 1 in 10,000 for a conventional antigen. 3. Toxic shock — Massive cytokine release (IL-2, TNF, IFN-γ) leads to toxic shock. 4. Examples — TSST-1 and enterotoxins of S. aureus; SpeA and SpeC of group A streptococcus. 5. A-B toxins — The B subunit binds a receptor; the A subunit is the toxic enzyme (cholera toxin, E. coli LT, Shiga toxin, pertussis toxin). 6. Pore-forming toxins — They pierce the target cell membrane and lyse it (S. aureus alpha-toxin, streptolysin O).SuperantigenAntigen-presenting cellMHC IIT cellTCR (Vβ)SAgUp to 50% of T cells activated(conventional antigen: 1 in 10,000)Massive IL-2, TNF, IFN-γ→ toxic shockTSST-1, enterotoxins (S. aureus);SpeA, SpeC (group A streptococcus)Other exotoxinsA-B toxinB: bindingA: enzymePore-formingtoxinLysis
  • Toxin, damage
  • Host (cells, tissues)
  • Immunity
  • Clinical consequence
  • Pathogen

Key points

  • Superantigen: MHC II–Vβ bridge, up to 50% of T cells activated.
  • Cytokine storm and toxic shock: TSST-1, enterotoxins, SpeA, SpeC.
  • Other toxins target a cell: A-B (enzyme) or pore-forming (lysis).

Classic pitfall

Lumping all exotoxins together: only the superantigen massively activates T cells.

Related pathogen pages (6)

Sources

Educational content · Illustrative mechanisms · Not applicable to individual clinical decisions · MDR 2017/745

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