Within seconds to minutes (histamine, tryptase, leukotrienes)
High-YieldNEET PG
The hallmark of Type I is IgE-mediated, immediate-onset response. Sensitization occurs on first exposure; clinical reaction on re-exposure.
Why Option 3 Is Incorrect
IgG is NOT the predominant immunoglobulin in Type I hypersensitivity. IgG plays a role in:
Type II cytotoxic hypersensitivity (antibody-mediated cell destruction)
Type III immune complex disease (IgG + antigen → circulating immune complexes)
Type IV delayed-type hypersensitivity (IgG does NOT participate; this is T-cell mediated)
Clinical Pearl
While IgG antibodies can form against allergens (e.g., in chronic allergen exposure), they do NOT trigger the acute degranulation characteristic of Type I reactions. IgE is the sole mediator of immediate hypersensitivity.
