USA Biology Olympiad (USABO) Practice Exam

What type of immunoglobulin is responsible for causing allergic reactions?

1. IgM

2. IgA

3. IgD

4. IgE

The correct answer is: IgE

The immunoglobulin that plays a key role in allergic reactions is IgE. This antibody is specifically involved in the body's immune response to allergens, such as pollen, pet dander, and certain foods. When an individual is exposed to an allergen for the first time, IgE antibodies are produced. These antibodies bind to specialized cells called mast cells and basophils. Upon subsequent exposure to the same allergen, the IgE antibodies trigger these mast cells and basophils to release histamine and other inflammatory mediators. This histamine release is what leads to the symptoms commonly associated with allergic reactions, such as itching, swelling, and other inflammatory responses. In contrast, other immunoglobulins like IgM, IgA, and IgD have different primary functions. IgM is generally the first antibody produced in response to an infection, providing an initial immune defense. IgA is vital for mucosal immunity and is often found in secretions such as saliva and tears. IgD is primarily involved in the activation and regulation of B cells during an immune response. Thus, IgE is uniquely identified with the hypersensitivity reactions characteristic of allergies.