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.</p> | 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.</p> |