A patient undergoing allergy testing experiences a severe reaction post-injection. Which mechanism explains why localized wheal formation occurs at the allergen injection site?

💡 Explanation

Wheal formation in allergy testing results from localized mast cell degranulation. The mechanism involves crosslinking of IgE antibodies bound to mast cell surfaces upon allergen exposure, which then triggers histamine release. Because histamine increases vascular permeability, fluid leaks into the tissue, therefore causing the characteristic wheal, rather than complement lysis or T-cell activation.

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