Sites of B Lymphocyte Selection, Activation, and Tolerance in Spleen

The immune system appears to be rigid, restricting one lymphocyte to make one antibody (1) and the peripheral B cell pool to a constant number (10⁸ in mice) (2– 4). To make a rapid immune response to an unlimited number of antigens at any anatomical site, it has developed at least three major strategies: (a) continuous production of 2 × 10⁷ lymphocytes/d from bone marrow (mice; 5), displaying a part of the 10¹¹ potential immunoglobulin repertoire (6); (b) the establishment of a long-lived B cell pool (10⁸), under the influence of environmental antigens (7) or an idiotypic network (8, 9); and (c) the ability of long-lived B cells to migrate between different lymphoid tissues (10, 11), thus monitoring sites of antigen invasion. Since the 10^8...