Biol. 1. Also called B lymphocyte. a type of lymphocyte, developed in bone marrow, that circulates in the blood and lymph and, upon encountering a particular foreign antigen, differentiates into a clone of plasma cells that secrete a specific antibody and a clone of memory cells that make the antibody on subsequent encounters.
2. Also called beta cell. a cell in the islet of Langerhans that produces and secretes insulin.