B cell

B cells, also known as B lymphocytes, are a type of white blood cell of the lymphocyte subtype. They play a crucial role in the adaptive immune system by mediating humoral immunity. The primary function of B cells is to produce antibodies against specific antigens.

B cell development begins in the bone marrow (hence "B" cell), where they undergo V(D)J recombination to generate a diverse repertoire of antigen receptors, called B cell receptors (BCRs). Each B cell expresses a unique BCR on its surface. This receptor is essentially a membrane-bound antibody molecule.

When a B cell encounters an antigen that binds to its BCR, it becomes activated. This activation process often requires T cell help, particularly from helper T cells (specifically, T follicular helper cells). Activated B cells undergo clonal expansion, proliferating and differentiating into either plasma cells or memory B cells.

Plasma cells are short-lived, antibody-secreting cells that produce large quantities of antibodies specific to the triggering antigen. These antibodies circulate in the blood and lymph, neutralizing pathogens, marking them for destruction by other immune cells (e.g., through opsonization), or activating the complement system.

Memory B cells are long-lived cells that remain in the body after the infection has cleared. If the same antigen is encountered again in the future, these memory B cells can quickly differentiate into plasma cells, leading to a faster and more effective antibody response – this is the basis of immunological memory and vaccination.

Different subtypes of B cells exist, each with specialized functions. Examples include marginal zone B cells, follicular B cells, and B1 cells. These subtypes contribute to different aspects of humoral immunity and respond to different types of antigens.

Dysregulation of B cell function can lead to various autoimmune diseases and B cell malignancies, such as lymphomas and multiple myeloma. The study of B cells is therefore essential for understanding immune function and developing treatments for immune-related disorders.