Which immunoglobulin class is involved in immediate hypersensitivity reactions?

The immunoglobulin class specifically involved in immediate hypersensitivity reactions is IgE. This type of antibody plays a critical role in allergic responses and is associated with the activation of mast cells and basophils. When an individual is exposed to an allergen, IgE antibodies bind to specific receptors on these cells. Upon subsequent exposure to the same allergen, it triggers the release of mediators such as histamine, leading to the symptoms associated with immediate hypersensitivity, like asthma, hay fever, and anaphylaxis.

In contrast, other immunoglobulin classes serve different functions. IgA is primarily found in mucosal areas and protects mucosal surfaces. IgM is the first antibody produced in response to an infection and is involved in the initial stages of the immune response. IgG is the most abundant immunoglobulin in serum and plays a significant role in long-term immunity and in opsonization of pathogens. These roles do not pertain to the immediate hypersensitivity reactions that IgE is specifically designed to mediate.