Which immunoglobulin class is most associated with immediate allergic reactions (Type I hypersensitivity) and binds to receptors on mast cells and basophils?

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Immediate allergic reactions are driven by IgE antibodies that sensitize mast cells and basophils by binding to high-affinity Fc receptors on their surfaces. When an allergen reappears and cross-links these bound IgE molecules, it triggers rapid degranulation of the cells, releasing histamine and other mediators that produce the sudden symptoms of Type I hypersensitivity. Although other antibody classes exist (IgG, IgA, IgM), they do not mediate this classic immediate allergic pathway: IgG primarily handles opsonization and some inflammation via complement, IgA protects mucosal surfaces, and IgM is the initial antibody of an immune response and also activates complement but does not drive mast cell/basophil degranulation in the same way.