AEMCA Practice Exam

Which immune response mediator is most likely to trigger an anaphylactic reaction?

1. IgA

2. IgM

3. IgG

4. IgE

The correct answer is: IgE

The mediator most likely to trigger an anaphylactic reaction is IgE. This immunoglobulin plays a critical role in allergic responses and is specifically associated with hypersensitivity reactions, particularly type I hypersensitivity. When an individual is exposed to an allergen for the first time, IgE antibodies are produced and bind to mast cells and basophils. Upon subsequent exposures to the same allergen, the allergen cross-links the bound IgE on these cells, leading to their degranulation. This release of mediators such as histamine and other inflammatory chemicals can result in the rapid onset of symptoms associated with anaphylaxis, including swelling, difficulty breathing, and a rapid drop in blood pressure. In contrast, IgA, IgM, and IgG are involved in different aspects of the immune response. IgA primarily protects mucosal surfaces, IgM is the first antibody produced in response to an infection, and IgG is associated with long-term immunity and memory responses but does not typically mediate anaphylaxis. Understanding the role of each immunoglobulin helps clarify why IgE is the primary mediator linked to anaphylactic reactions.