Final answer:
A plasma cell secretes antibodies of a single specificity, identical to the parent B-cell's receptors. These cells are specialized to produce large amounts of antibodies, targeting a specific antigen for the immune response.
Step-by-step explanation:
A plasma cell secretes antibodies of a single specificity that are related to that on the surface of the parent B-cell. Once a B-cell is activated by an antigen, it undergoes clonal proliferation, and the daughter cells differentiate into plasma cells. These plasma cells act as antibody factories, producing large quantities of antibodies. Specifically, they secrete pentameric IgM molecules that have the same antigen specificity as the B-cell receptors (BCRs) they originated from. The singular specificity of the antibodies ensures that each antibody can bind to only one kind of antigen, marking it for destruction.