Anaphylaxis Alert Wristband. Core Pathology Question


A young boy with known peanut allergy presents with an anaphylactic reaction after eating Thai food. Which one of the following statements is most true of the pathophysiology of this condition in this boy?

a. Antigen binding to surface IgM has triggered mast cell degranulation

b. Antigen binding to surface IgE has triggered mast cell degranulation

c. Antigen has directly stimulated neutrophil mediated inflammation

d. Antigen has directly stimulated mast cell degranulation

e. Antigen binding to surface Ig has triggered neutrophil degranulation




The answer is b.


NICE Defines anaphylaxis as “a severe, life-threatening, generalised or systemic hypersensitivity reaction. It is characterised by rapidly developing, life-threatening problems involving: the airway (pharyngeal or laryngeal oedema) and/or breathing (bronchospasm with tachypnoea) and/or circulation (hypotension and/or tachycardia). In most cases, there are associated skin and mucosal changes.” It is a type I hypersensitivity reaction.

Anaphylaxis requires pre-sensitisation. During the initial exposure to an antigen, antigen specific IgE is produced and attached to the surface of mast cells. During  subsequent exposure(s), the antigen binds and crosslinks surface IgE triggering  mast cell degranulation and release of inflammatory mediators most notably histamine but also serotonin, bradykinin and others. This may occur locally and cause a local inflammatory condition (allergic rhinitis for example) or systemically where the inflammatory response causes the life threatening features of anaphylaxis.

Mast cells are produced by the bone marrow from where they migrate to many different body tissues. They are found in high number in sub-epithelial (sub-cutaneous and sub-mucosal) tissues and around blood vessels and nerves.  Hence, skin rashes (hives), swelling (angioedema), bronchospasm and vascular changes are prominent.

In many cases of anaphylaxis, an initial immediate reaction is followed by a late phase reaction, usually 2-8 hours after the initial exposure (rarely up to 24 hours). This late phase reaction happens due to the infiltration of tissues with eosinophils, basophils, neutrophils, monocytes and CD4+ T cells.



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