B-Cell Development and Differentiation

The establishment of the mature B-cell pool involves a delicate balance that ensures a broad spectrum of specificities and at the same time avoids self-reactivity. B lymphocytes develop from hematopoietic stem cells and their progeny are characterized by a specific B-cell receptor (BCR), which is generated in a somatic rearrangement process. Only when B cells are activated and differentiate into plasma cells will the BCR be secreted in the form of antibodies into the body's fluids. If T-cell help is provided, B cells expressing an immunoglobulin M (IgM) BCR may switch in a germinal center reaction to the Ig classes IgG, IgA, or IgE. In addition, the genes encoding the BCR can be further diversified through hypermutation. Those B cells with a high-affinity receptor are selected to differentiate into long-lived memory B and plasma cells. This B-cell differentiation requires organized immune structures. In inflamed tissues, ectopic lymphoid tissue may develop to support local B-cell differentiation.