Which antibody is primarily involved in Type 1 hypersensitivity reactions?

Type 1 hypersensitivity reactions, also known as immediate hypersensitivity reactions, are primarily mediated by the antibody IgE. This type of hypersensitivity occurs when an individual is exposed to an allergen, leading to the activation of B cells that produce IgE.

IgE antibodies bind to allergens and mediate the degranulation of mast cells and basophils, resulting in the release of histamine and other inflammatory mediators. These substances lead to the symptoms commonly associated with allergic reactions, such as itching, bronchoconstriction, and vasodilation. In contrast, other immunoglobulins like IgG, IgA, and IgM are involved in different immune responses but do not play a significant role in the immediate manifestations of Type 1 hypersensitivity.

Therefore, the involvement of IgE is critical in the pathophysiology of allergic reactions, making it the correct answer for this question.