What is the mechanism of anaphylaxis during subsequent exposures to allergens?

Anaphylaxis is a severe allergic reaction that occurs upon subsequent exposure to an allergen. The mechanism that underlies this reaction involves the binding of antigens (allergens) to IgE antibodies that are already bound to mast cells. When an individual is exposed to an allergen for the first time, their immune system produces IgE antibodies specific to that allergen. These antibodies attach to mast cells and basophils, sensitizing them to future exposures.

Upon re-exposure to the same allergen, the antigen binds to these IgE antibodies already present on the mast cells. This cross-linking of the IgE antibodies triggers mast cell degranulation, leading to the release of a variety of mediators, including histamine, leukotrienes, and prostaglandins, which contribute to the symptoms of anaphylaxis such as vasodilation, increased vascular permeability, bronchoconstriction, and tissue swelling.

This mechanism is what differentiates anaphylaxis from other types of allergic reactions and highlights the role of IgE and mast cells in the rapid and severe response seen during anaphylactic events.