What happens during an IgE-mediated reaction?

• A. IgE antibodies trigger inflammation and histamine release, leading to vasodilation and capillary permeability
• B. They are mediated by T helper 1 cells only
• C. They cause immediate cytotoxic destruction of bacteria
• D. They involve formation of immune complexes in joints

Answer: (A)

The main idea is IgE-mediated immediate hypersensitivity. In this type of reaction, exposure to an allergen prompts B cells to produce IgE that binds to high-affinity receptors on mast cells and basophils. When the allergen is encountered again, it cross-links these bound IgE molecules, causing rapid degranulation and release of histamine and other mediators. Histamine then drives vasodilation and increased capillary permeability, leading to redness, swelling, and itchiness and, in more severe cases, anaphylaxis.

This is distinct from other immune pathways: T helper 1 cells are more involved in cell-mediated responses (not the classic IgE-driven allergy), immediate cytotoxic destruction of bacteria isn’t the mechanism of IgE allergies, and immune complex formation in joints describes a different hypersensitivity (type III).