What are the types of B cells that contribute to immune responses?

Plasma cells - antibody secretion Memory cells- IgG expressing B cells - isotope switching High affinity ig-expressing B cells- affinity maturation B-1 cells -localized in mucosal tissues and peritoneum. Express receptors of limited diversity and secrete IgM that can be produced without stimulation with antigen (natural antibodies). IgM+IgD+ lymphocytes are mature B cells that can respond to antigens. Why both classes of Ig are needed is unknown.