Ontogeny of the antibody-forming cell line in mice. I. Kinetics of appearance of mature B cells.

The development of functionally mature B cells in the liver and spleen of fetal and neonatal CBA mice has been followed. A mature B cell is defined as one giving rise to antibody-producing progeny within 2 days in culture. Very few such B cells are found during fetal life. After birth there is a rapid rise in the numbers reaching 1/3 of adult levels in the 7-day-old spleen.