B lymphocytes, also known as B cells, are one of the five types of white blood cells, or leukocytes, that circulate throughout the blood. They and T lymphocytes are the most abundant types of white blood cells. B lymphocytes are a vital part of the body's immune system. They function to specifically recognize a foreign protein, designated as an antigen, and to aid in destroying the invader.

B lymphocytes are produced and mature in the bone marrow. The mature form of the cell is extremely diverse, with a particular B cell being tailored to recognize just a single antigen. This recognition is via a molecule on the surface of the B cell, called a B cell receptor. There are thousands of copies of the identical receptor scattered over the entire surface of a B cell. Moreover, there are many thousands of B cells, each differing in...