[Origin and development of B1 lymphocytes. A cell population involved in defence and autoimmunity].

B1 lymphocytes are an anatomically, phenotypically, and functionally distinct subset of B cells producing the bulk of natural serum IgM in the absence of any apparent stimulation by specific antigens. These cells are a dominant population of B cells in peritoneal and pleural cavities and they have characteristics of activated cells and higher cell size and cytoplasmic complexity than conventional B cells. B1 cells spontaneously secrete antibodies and operate under a differentiation program that is unique and differs from the paradigm associated with Ig-secreting B-2 cells. The antibodies produced by B1 cells may participate in a variety of physiological activities since they are involve in immune regulation, clearance of senescent and apoptotic cells and resistance to infection. However, it has been suggested that they are also involved in autoimmunity. Many advances have been made to describe the origin, development and differentiation of B1 cells, which will be examined here.