B cells
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Also called B lymphocytes
So named as they were initially found in the Bursa of Fabricius. They produce antibodies (Ig’s) and are associated with humoral immunity. They represent 20-30% of circulating lymphocytes. B cells have B cell receptors (BCR), or antigen binding sites. This is IgM when the B cell is immature, changing to IgD when the cell is mature. B cells also express MHC II, CD9, CD,19, CD20 and CD24.
Under antigenic stimulation they differentiate into plasma cells and memory cells.
B-cells also act as Antigen-Presenting Cells (APCs) by presenting digested fragments to T-cells on MHC II.
For more on B cell differentiation, see here.