What antibody class is primarily involved in anaphylaxis (immediate hypersensitivity)?

• A. IgA
• B. IgG
• C. Immunoglobulin E (IgE)
• D. IgM

Answer: (C)

Immediate hypersensitivity reactions are driven by immunoglobulin E. IgE binds to high-affinity receptors on mast cells and basophils; when an allergen cross-links these IgE molecules, the cells degranulate and release histamine and other mediators within minutes. This rapid mediator release causes the symptoms of anaphylaxis: sudden vasodilation, increased vascular permeability, airway constriction, and edema. Other antibody classes have different roles—IgG and IgM are involved in other immune responses and do not mediate this classic rapid, systemic reaction, while IgA mainly protects mucosal surfaces and does not initiate anaphylaxis.