Table 2

Major mediators of anaphylaxis9 13 18 44 50–52 57

Mediators / cellsAction
Histamine (via H1–H4 histaminergic receptors)
  • Pruritus, tachycardia, rhinorrhoea, bronchospasm (H1)

  • Endothelial release of nitric oxide (NO) leading to vasodilatation and hypotension (H1)

  • Hypotension, flushing and headache (H1, 2)

  • Inhibitory presynaptic (H3)—release endogenous epinephrine

  • Chemotaxis and mast cell cytokine release (H4)

  • Activates: complement, coagulation and kalikrein–kinin system leading to angioedema, hypotension, and disseminated intravascular coagulation

  • Respiratory and gastrointestinal tract mast cells contain less tryptase than connective tissue mast cells (tryptase may not increase in food anaphylaxis)

Platelet activating factor (PAF)
  • Responsible for systemic mast cell activation; high concentration of PAF and low concentrations of PAF-acetylhydrolase may predispose to severe reaction

  • Low serum ACE concentrations may also contribute to severe anaphylaxis

  • Pro-inflammatory (release mediators from their granules)

  • Anti-inflammatory (metabolise vasoactive substances)