Final answer:
IgD maintains the same specificity as IgM through isotype switching. This process involves rearrangement of gene segments encoding the antibody’s constant region while preserving the variable region responsible for antigen binding.
Step-by-step explanation:
IgD is able to become a surface receptor that has the same specificity as an IgM through the process known as isotype switching. This process occurs after initial secretion of IgM, where cytokines secreted by helper T cells stimulate the B cells to change from IgM production to other isotypes like IgG, IgA, or IgE while retaining the original epitope specificity. Class switching is achieved by genetic rearrangement of gene segments encoding the constant region (C region) of the antibody. However, this rearrangement does not alter the variable region (V region) that determines the antigen-binding specificity; hence IgD maintains the same specificity for the antigen as IgM.