Final answer:
IgM and IgD are co-expressed on naive B cells through a process called 'allelic exclusion', which enables B cells to express a single species of BCR. Following antigen recognition and helper T cell interaction, naive B cells can differentiate into plasma cells, a process involving DNA rearrangement known as 'V(D)J recombination' to produce specific immunoglobulins.
Step-by-step explanation:
IgM and IgD are co-expressed on naive B cells by a process called 'allelic exclusion'. This ensures that each B cell expresses a single species of the B cell receptor (BCR) and hence a specificity for a single antigen. Naive B cells express membrane-bound IgM and IgD, which act as receptors for antigens. Upon encountering an antigen, the B cells can undergo clonal selection, differentiating into plasma cells that secrete various antibodies, including IgM, and further maturing into memory B cells.
The IgM receptors on the B cells recognize and bind to antigens, leading to phagocytosis and antigen degradation. These presented antigen fragments in combination with MHC-II are recognized by helper T cells, which facilitate B cell differentiation into antibody-secreting plasma cells through cytokine signaling. This differentiation occurs by DNA rearrangement in a process known as 'V(D)J recombination', which produces a protein immunoglobulin that binds specifically to the antigen, inactivating it.