Allergic Response

Allergic anaphylaxis is an example of immediate type 1 hypersensitivity. The patient becomes sensitised to an allergen. On a further exposure to that allergen, the responsible allergenic antigen binds to an antigen-specific IgE antibody, leading to mast cell degranulation. The response is caused by the binding of an antigen to an antigen-specific antibody leading to mast cell degranulation. Histamine and other mediators, including leukotrienes, tumour necrosis factor and various cytokines, are released from mast cells and basophils following exposure to this antigen. This causes:

• Increased bronchial smooth muscle tone causing wheeze and shortness of breath
• Decreased vascular tone
• Increased capillary permeability leading to hypotension and an urticarial rash

The response is usually uniphasic, reported biphasic response varies from 1-20%.