Development of B-lymphocyte colony-forming cells in foetal mouse tissues

In CBA and (CBA X C57B1)F1 mice, cells forming B-lymphocyte colonies in agar culture were first detected in the 17-day foetal liver and the following day in the spleen, bone marrow and peripheral blood. Colony-forming cells were not detected in the yolk sac or foetal thymus. Adult levels of colony-forming cells were achieved within 3 days of birth. In organ cultures of 15-day foetal liver or spleen, B-lymphocyte colony-forming cells developed during a 5-day incubation period, indicating that both organs can function as bursal analogues. Foetal liver colony-forming cells were of small size and generated colonies of cells with a pattern of membrane immunoglobulin similar to colony cells generated by cells from adult animals.