BZellen

BZellen, commonly written B-Zellen in German, denotes B lymphocytes, a class of white blood cells that form part of the humoral branch of the adaptive immune system. The name B is historically derived from the Bursa of Fabricius, an organ in birds where B cells were first described; in mammals these cells mature in the bone marrow, and the term B cell remains standard.

Development and activation: BZellen originate from hematopoietic stem cells in the bone marrow and differentiate into naive B cells. When their B cell receptor binds a specific antigen and, in most cases, with help from helper T cells, BZellen become activated and can differentiate into antibody-secreting plasma cells and into memory B cells for rapid responses upon re-exposure.

Function and processes: BZellen express B cell receptors that recognize a wide range of antigens. Upon activation, they proliferate and secrete antibodies that neutralize pathogens or mark them for destruction. BZellen also present antigen via MHC class II to T cells and, in germinal centers, undergo somatic hypermutation and class switch recombination, increasing antibody affinity and diversity.

Clinical relevance: BZellen are central to protective immunity against extracellular pathogens and to the effectiveness of most vaccines. Abnormal BZellen activity is linked to autoimmune diseases and to B cell–related cancers. Therapeutic strategies include antibodies that deplete BZellen and approaches to modulate B cell function.

See also: B lymphocytes; humoral immunity; immunoglobulins; germinal center; plasma cell.