A patient undergoing allergen immunotherapy experiences a localized skin reaction, despite gradually increasing allergen doses. Why does this localized reaction persist during desensitization?

💡 Explanation

Localized reactions persist because mast cells, already sensitized with IgE, degranulate and release histamine upon encountering the allergen, therefore causing inflammation and itching at the injection site, rather than systemic anaphylaxis, due to the localized nature of the exposure and limited allergen diffusion.

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