IgE-mediated reactions are associated with which type of hypersensitivity?

• A. Type I
• B. Type II
• C. Type III
• D. Type IV

Answer: (A)

IgE-mediated reactions are associated with immediate hypersensitivity, also known as type I hypersensitivity. In this process, IgE antibodies bind allergens and attach to mast cells and basophils. When the allergen is encountered again, it cross-links the IgE on these cells, triggering rapid degranulation and release of mediators like histamine, leukotrienes, and prostaglandins. This leads to quick-onset symptoms such as itching, hives, nasal congestion, bronchoconstriction, and in severe cases anaphylaxis.

The other hypersensitivity types involve different mechanisms: cytotoxic reactions are driven by IgG or IgM targeting cells, immune complexes form and deposit in tissues causing inflammation, and delayed-type hypersensitivity is mediated by sensitized T cells releasing cytokines.