ABSTRACT
B lymphocytes originate in the primary lymphoid organs, which in mice and humans include primarily the fetal liver and the bone marrow, where they assemble antibody genes unique to each cell. The cells undergo a rather complex set of ordered maturation steps guided by, and in turn controlling, the expression of the cell’s immunoglobulin chains. The cell surface-bound IgM antibody molecules that are ultimately formed are specialized to act as cell surface antigen receptors and are not secreted, linking the specificity of the antigen receptor to the antibody that may eventually be produced.
