Mast cell mediators: relevant to chronic urticaria.
Mediator
Effect in chronic urticaria
Preformed mediators
Histamine
Direct potent vasoactive and smooth muscle spasmogenic effects Principal mediator of vascular changes [70, 71]
Newly synthesised mediators
Lipid mediators
LTC4 LT B4 PGD2
Actions similar to histamine Potentiate vasodilatation, vascular permeability, and smooth muscle contraction Chemotactic for neutrophils and eosinophils [72]
Cytokines and chemokines
Tumour necrosis factor-alpha
Newly synthesised as well as preformed
Upregulates expression of adhesion molecules on endothelial cells Promotes leukocyte rolling and adhesion Chemotactic for neutrophils [73]
Interleukin-1
Proinflammatory cytokine Lymphocyte activator [74] Activates mast cells after release from leukocyte [75]
Interleukin-4
Chemotactic for neutrophils Recruits eosinophils [76]
Member of C X C chemokines Potent neutrophil chemoattractant Involved in neutrophil degranulation, respiratory burst, and adhesion to endothelial cells [79]