Final answer:
Plasma cells, differentiated from B cells, are specialized to secrete antibodies. They initially secrete pentameric IgM, followed by other types such as IgG, IgA, and IgE, due to class switching.
Step-by-step explanation:
Plasma Cells and Antibody Secretion
Plasma cells do not have surface immunoglobulins (Ig) or B cell receptors (BCRs) but instead secrete antibodies as their function. Once a B cell is activated and differentiates into a plasma cell, it turns into an antibody-producing factory, primarily secreting pentameric IgM. This is followed by class switching under the influence of cytokines secreted by T-helper cells, leading to the production of other types of immunoglobulins such as IgG, IgA, and IgE, all of which have the same antigen specificity as the original BCRs.
Different immunoglobulins serve specific roles in the immune response. IgM, which makes up about ten percent of all antibodies, is able to bind ten identical antigens due to its pentameric structure. IgG is the most common antibody, ideal for secondary immune responses. IgA is found in mucosal areas and body secretions such as tears, saliva, and breast milk, and provides local protection. IgE is mainly involved in allergic responses and parasitic infections. Lastly, IgD, which is present in small amounts, plays a role in B cell maturation.