Which class of antibody is mainly found on the B cell surface as an antigen receptor?

• A. IgG
• B. IgE
• C. IgA
• D. IgD

Answer: (D)

The class of antibody primarily found on the surface of B cells as an antigen receptor is IgD. This antibody plays a crucial role in the immune response by serving as a receptor for antigens. When the IgD on the B cell binds to its specific antigen, it triggers the activation and proliferation of the B cell, leading to the production of antibodies.

While other classes of antibodies, such as IgG, IgE, and IgA, have crucial functions in immune response and protection, they do not primarily serve as antigen receptors on the surface of B cells. IgG is the main antibody in blood and tissue, providing long-term immunity; IgE is involved in allergic reactions and response to parasites; and IgA is predominantly found in mucosal areas and secretions. Therefore, IgD's specific role and location as an antigen receptor on B cells make it the correct answer in this context.