Which immunoglobulin is primarily involved in allergic responses?

The immunoglobulin primarily involved in allergic responses is IgE. This antibody plays a crucial role in the body's immune response to allergens. When an individual is exposed to an allergen, IgE antibodies bind to the allergen and trigger the activation of mast cells and basophils, which release histamine and other inflammatory mediators. This process leads to the symptoms associated with allergies, such as itching, sneezing, and inflammation.

IgE is unique among immunoglobulins due to its low concentration in the serum compared to others, yet it is highly potent in mediating allergic reactions. This specificity and sensitivity make IgE the key player in the immediate hypersensitivity response that characterizes allergic disorders like asthma, hay fever, and anaphylaxis.

In contrast, the other immunoglobulins listed play different roles in the immune response. IgA is primarily involved in mucosal immunity, found in secretions such as saliva, tears, and breast milk. IgD has a role in initiating B cell activation but is present in very low levels in the serum. IgM is the first antibody produced in response to an infection and plays a key role in the early stages of immune responses but is not specifically linked to allergic reactions.