B cells develop in bone marrow and undergo antigen-induced activation and terminal differentiation in germinal centres of secondary lymphoid organs. Each B cell is a clone which means that an individual B cell has a unique genetic code and produces only one type of antibody when stimulated by antigen being able to multiply itself and originate several B cells with the same antigen specificity (clonal selection theory). However their important role in adaptive immune responses is supported by the remarkable capacity of recognizing an unlimited array of antigens due to mechanisms of antibody diversity such as V(D)J recombination class switching and somatic hypermutation. B cells can also function as antigen presenting cells that can activate T cells improving the effectiveness of the immune response. Immune B cell tolerance surveillance through clonal deletion anergy and receptor editing is also necessary to avoid pathological conditions like autoimmune diseases. B cells can contribute to autoimmunity by autoantibody production cytokine synthesis antigen presentation T cell activation and ectopic lymphogenesis.