B lymphocyte subpopulation defined by a rat monoclonal antibody, 14G8

14G8 is monoclonal rat antibody that recognizes an antigen found on 30 to 40% of B lymphocytes from normal mice and on approximately 65% of B lymphocytes from mice with the xid-determined immune defect. 14G8+ B cells from normal mice resemble B cells from mice with the xid-determined defect in that the median amount of membrane IgM expressed per cell is much larger than that of 14G8- B cells. The frequency of 14G8+ cells is highest in neonatal mice (approximately 55% of all spleen cells) and falls with age to approximately 25% of all spleen cells in adult mice. Relatively few lymph node or bone marrow B cells express the antigen recognized by 14G8. 14G8 also reacts with 50% of resident peritoneal cells and with red blood cells. 14G8+ and 14G8- B cell preparations were obtained by fluorescence-activated cell sorting and by adherence to 14G8 coated dishes. 14G8+ cells responded with in vitro proliferation to both anti-mu and to LPS. Cell cycle analysis indicated that approximately 33% of these cells entered S phase in response to LPS and 38% in response to anti-mu. In contrast, 14G8- cells responded poorly to LPS (7% of cells entered S phase) although they showed good responses to anti-mu (40% of cells entered S phase). Thus, 14G8+ B cells, despite their similarity to B cells from mice with the xid defect, can proliferate to anti-mu, which B cells from defective mice fail to do. 14G8 provides a monoclonal antibody valuable in the description of functional B cell subpopulations.