Final answer:
Plasma cells are activated B cells that secrete antibodies. They do not normally circulate in peripheral blood.
Step-by-step explanation:
Plasma cells are activated B cells that secrete antibodies. They are like antibody factories, producing many copies of a single type of antibody. The antibodies travel throughout the body in blood and lymph. However, unlike memory cells, plasma cells do not normally circulate in peripheral blood. They often leave the secondary lymphoid organs and migrate back to the bone marrow, where the differentiation process started.