Type I hypersensitivity is primarily mediated by IgE antibodies, which bind to allergens and trigger mast cell degranulation and release of histamine, leading to immediate allergic reactions. This mechanism is distinct from other hypersensitivity types that involve different antibodies or immune cells. IgE's role in rapid onset reactions such as anaphylaxis and allergic asthma defines Type I hypersensitivity as immediate and antibody-dependent.

Reference: Abbas AK, Lichtman AH, Pillai S. Cellular and Molecular Immunology, 9th Edition, Chapter 11: Hypersensitivity Reactions, p. 406-410.