Abstract
We have used a panel of monoclonal antibodies to examine the development of lymphoid and myeloid sub-populations of cells in thymus, bone marrow, and liver of 16 fetuses from 12 to 16 weeks of gestational age. Pre-B and IgM+ B cells were present at a ratio of approximately 2:1 in all of the fetal bone marrow and liver samples; cells of both phenotypes were HLA-DR+ but did not express the mature B-cell antigen, HB-2. Cells expressing the myelomonocytic antigen, MMA or Leu-M1, were more frequent in bone marrow (40%) than in fetal liver (10%), and cells expressing the HNK-1 or Leu-7 antigen were rare (+ cells were never seen in these hemopoietic tissues. These results suggest that fetal liver and bone marrow precursors in humans do not express these T-cell antigens prior to thymic entry and the onset of thymocyte differentiation.