Hemopoiesis in human fetal and embryonic liver

In this review, we describe the topographic distribution of hemopoietic cells of the lymphoid, myeloid, and erythroid lineages in the human fetal and embryonic liver. The data are based on studies of frozen tissue, allowing the determination of a broad range of hemopoietic antigens, and studies on paraffin-embedded tissue, allowing the combination of optimal morphology and immunodetection of lineage-specific antigens. The different hemopoietic lineages each show their own immunophenotype and distribution; intercellular and microenvironmental relationships were easily determined. In a few cases, some scarce CD34-positive early progenitor cells were seen. The number of proliferating cells, identified by monoclonal antibody (MAb) Ki-67, varied from 350 to 2500 (median = 1,500) per square millimeter of tissue. Erythroid cells reacted with antisera to glycophorin A, CDw75, and CD43 and partly surround a central macrophage, whereas the myelomonocytic cells reacted with CD45, CD43, CD74, and antilysozyme serum, and with LN3 from 14 weeks onward. Myelopoietic (CD15 positive) cells were localized mainly around portal triad vessels and increased in number with gestational age. The lymphoid cells showed CD45, CD43, CD45RA/MT2, CD45RA/MB1, MB2, and CD74 reactivity. B cells and their precursors were scattered among the hepatocytes without any sign of focal development in the age range studied. We seldom found cells positive for delta-H chain or C3bR (CD35); C3dR (CD21)-positive cells were even more scarce. Cells reactive with MAb WT1 (CD7) were present in a scattered single pattern (< or = 20/mm2) among the parenchymal cells; cells expressing mature T-cell markers (CD2, CD3, CD5) were rare. Large (> 15 mu) CD43-positive hemopoietic cells in the fetal liver were distinguished that exclusively expressed CD43, probably representing early hemopoietic progenitor cells.