What does IgD primarily function as in the immune response?

IgD primarily functions as a receptor for B cell activation. It plays a crucial role in the early stages of the immune response. When antigens bind to the IgD found on the surface of B cells, it triggers those B cells to become activated. This activation leads to clonal expansion and differentiation into plasma cells or memory B cells, which are essential for producing specific antibodies in response to pathogens.

While other immunoglobulin classes have specific roles—like IgE in mediating allergic responses or IgG in neutralizing toxins—IgD's primary role is associated with B cell maturation and immune signaling rather than directly engaging in pathogen neutralization or allergic reactions. Its presence on naive B cells serves as a marker for their readiness to respond to specific antigens once exposed. This makes understanding IgD's role vital for comprehending the broader immune response mechanism and the functionality of B cells in adaptive immunity.