B cell differentiation B cell differentiation B cells are about 6um in diameter, and have a thin rim of cytoplasm around the nucleus. They look very much like other lymphocytes, especially T cells. Plasma cells, on the other hand are unique. They are about 15 um in diameter and contain abundant endoplasmic reticulum in the cytoplasm. This ER is of course necessary for the production of antibodies - the purpose of the plasma cell.
B cells start their life in the bone marrow as pre-B cells.
These cells do not have antibody on their surface. An encounter with antigen, along with help from T cell cytokines, stimulates B cell activation and differentiation into a plasma cell. The differentiation of B cells into plasma cells occurs as the cell continues to divide in the presence of cytokines. Different cytokines are known to stimulate B cells to become plasma cells secreting different classes of antibodies such as IgG, IgA or IgM etc. Ask Dr. Lee .