Which antibody is primarily involved in allergic reactions and infections?

The antibody primarily involved in allergic reactions and responses to parasitic infections is Immunoglobulin E (IgE). It plays a critical role in the immune system's response by binding to allergens, which can trigger the release of histamines and other chemicals from mast cells and basophils. This release leads to the symptoms typically associated with allergic reactions, such as swelling, itching, and mucus production.

In the context of infections, IgE is particularly important in defending against certain types of pathogens, especially helminths (worms). When the immune system encounters these parasites, it ramps up IgE production to help expel them from the body.

While other antibodies like IgA, IgG, and IgM serve significant functions in the immune response, they do not primarily facilitate the allergic response in the same manner that IgE does. IgA is mainly found in mucosal areas and protects surfaces like the gut and respiratory tract, IgG is the most abundant antibody in circulation and is vital for long-term immunity and neutralizing toxins, and IgM is typically the first antibody produced in response to an infection. Thus, IgE's specific role in allergic reactions and parasitic infections distinguishes it as the correct answer.