Type I Hypersensitivity corresponds to which of the following?

• A. Autoimmune disorder causing tissue damage
• B. Immediate allergic reaction
• C. Delayed-type cell-mediated response
• D. Immunodeficiency causing decreased antibody production

Answer: (B)

Type I hypersensitivity is an IgE-mediated immediate allergic reaction driven by mast cell degranulation. After first exposure, B cells produce IgE that binds to mast cells and basophils; at a subsequent encounter with the same antigen, cross-linking of surface-bound IgE triggers rapid release of histamine and other mediators, causing symptoms within minutes. This immediacy explains why it’s described as an immediate allergic reaction and why conditions like allergic rhinitis, hives, and anaphylaxis can occur so quickly after exposure. Autoimmune tissue damage involves antibodies or cells acting against self in other hypersensitivity types; delayed-type hypersensitivity is a T-cell–mediated response that peaks after 24–72 hours; and immunodeficiency with decreased antibody production reflects a deficiency rather than an overactive hypersensitivity reaction.