B lymphocytes (B cells) are an essential component of the humoral immune response. Produced in the bone marrow, B cells migrate to the spleen and other secondary lymphoid tissues where they mature and differentiate into immunocompetent B cells. Part of the adaptive immune system, B cells are responsible for generating antibodies to specific antigens, which they bind via B cell receptors (BCR).
Activation of B cells occurs via antigen recognition by BCRs and a required co-stimulatory, secondary activation signal provided by either helper T cells or the antigen itself. This results in stimulation of B cell proliferation and the formation of germinal centers where B cells differentiate into plasma cells or memory B cells. Importantly, all B cells derived from a specific progenitor B cell are clones that recognize the same antigen epitope.
Plasma cells are found in the spleen and lymph nodes and are responsible for secreting different classes of clonally unique antibodies that are found in the blood. Following the primary response, a small number of B cells develop into memory B cells, which express high-affinity surface immunoglobulins (mainly IgG), survive for a longer period of time, and enable a rapid secondary response.