HEMATOPOIESIS IN HUMAN FETAL AND EMBRYONIC LIVER

In this review, we describe the topographic distribution of hemopoieti c cells of the lymphoid, myeloid, and erythroid lineages in the human fetal and embryonic liver. The data are based on studies of frozen tis sue, allowing the determination of a broad range of hemopoietic antige ns, 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 immunophenoty pe and distribution; intercellular and microenvironmental relationship s were easily determined. In a few cases, some scarce CD34-positive ea rly progenitor cells were seen. The number of proliferating cells, ide ntified by monoclonal antibody (MAb) Ki-67, varied from 350 to 2500 (m edian = 1,500) per square millimeter of tissue. Erythroid cells reacte d with antisera to glycophorin A, CDw75, and CD43 and partly surround a central macrophage, whereas the myelomonocytic cells reacted with CD 45, CD43, CD74, and antilysozyme serum, and with LN3 from 14 weeks onw ard. Myelopoietic (CD15 positive) cells were localized mainly around p ortal triad vessels and increased in number with gestational age. The lymphoid cells showed CD45, CD43, CD45RA/MT2, CD45RA/MB1, MB2, and CD7 4 reactivity. B cells and their precursors were scattered among the he patocytes without any sign of focal development in the age range studi ed. We seldom found cells positive for delta-H chain or C3bR (CD35); C 3dR (CD21)-positive cells were even more scarce. Cells reactive with M Ab WT1 (CD7) were present in a scattered single pattern (less than or equal to 20/mm(2)) among the parenchymal cells; cells expressing matur e T-cell markers (CD2, CD3, CD5) were rare. Large (>15 mu) CD43-positi ve hemopoietic cells in the fetal liver were distinguished that Exclus ively expressed CD43, probably representing early hemopoietic progenit or cells. (C) 1997 Wiley-Liss, Inc.