Mechanisms of urticaria
- mechanisms of urticaria can be either:
- immune-mediated - IgE located on the mast cells an basophils cross-links with the allergen and activates the cells e.g.- urticaria induced by medication (penicillin), foods
- complement-mediated - mast cells are activated directly by compliments ( mainly by C3a, C4a, and C5a) e.g.- serum sickness and transfusion reactions which cause the activation complement cascade leading to urticaria
- non-immune mediated - mast cells are activated by non IgE mechanisms e.g.- physical stimuli, alcohol, radiocontrast dye, and medications (opiates, vancomycin, aspirin)
- autoimmune-mediated - circulating auto-antibodies activates the mast cells (1)
- all of the above mentioned mechanisms lead to dermal mast cells degranulation in response to a variety of stimuli releasing mediators which produce vasodilatation, dermal oedema, and a perivascular infiltrate of lymphocytes and eosinophils (1). When deep dermis / subcutaneous tissues involved = angioedema
- vasoactive mediators commonly released during urticaria include:
- histamine
- prostaglandin D 2
- leukotrienes C 4 and D 4
- platelet activating factor
- cytokines (1)
Reference:
1. Zuberbier T, Abdul Latiff AH, Abuzakouk M, et al. The international EAACI/GA²LEN/EuroGuiDerm/APAAACI guideline for the definition, classification, diagnosis, and management of urticaria. Allergy. 2022 Mar;77(3):734-66.