What immunoglobulin type is primarily found on the surface of B-lymphocytes and assists in B cell activation?

The correct answer is IgD, which plays a crucial role in the immune system, particularly in the function of B-lymphocytes. IgD is primarily expressed on the surface of B cells and acts as a receptor for antigens. This binding of antigens to IgD triggers B cell activation, leading to the proliferation and differentiation of B cells into plasma cells, which produce antibodies.

IgD's structure and location allow it to effectively recognize and respond to specific antigens, which is essential for initiating the adaptive immune response. While other immunoglobulins like IgM or IgG are involved in later stages of the immune response, their roles differ significantly from that of IgD, highlighting its importance in the early activation and regulation of B-lymphocyte responses.