<P> B cells, also known as B lymphocytes, are a type of white blood cell of the lymphocyte subtype . They function in the humoral immunity component of the adaptive immune system by secreting antibodies . Additionally, B cells present antigen (they are also classified as professional antigen - presenting cells (APCs)) and secrete cytokines . In mammals, B cells mature in the bone marrow, which is at the core of most bones . In birds, B cells mature in the bursa of Fabricius, a lymphoid organ . (The "B" from B cells comes from the name of this organ, where it was first discovered by Chang and Glick, and not from bone marrow as commonly believed .) </P> <P> B cells, unlike the other two classes of lymphocytes, T cells and natural killer cells, express B cell receptors (BCRs) on their cell membrane . BCRs allow the B cell to bind to a specific antigen, against which it will initiate an antibody response . </P>

The differentiated b cells that produce and secrete large amounts of antibodies are called