title: Murine fetal liver macrophages bind developing erythroblasts by a divalent cation-dependent hemagglutinin.
abstract: During mammalian development the fetal liver plays an important role in hematopoiesis. Studies with the macrophage (M phi)-specific mAb F4/80 have revealed an extensive network of M phi plasma membranes interspersed between developing erythroid cells in fetal liver. To investigate the interactions between erythroid cells and stromal M phi, we isolated hematopoietic cell clusters from embryonic day-14 murine fetal liver by collagenase digestion and adherence. Clusters of erythroid cells adhered to glass mainly via M phi, 94% of which bound 19 +/- 11 erythroblasts (Eb) per cell. Bound Eb proliferated vigorously on the surface of fetal liver M phi, with little evidence of ingestion. The M phi could be stripped of their associated Eb and the clusters then reconstituted by incubation with Eb in the presence of divalent cations. The interaction required less Ca++ than Mg++, 100 vs. 250 microM for half-maximal binding, and was mediated by a trypsin-sensitive hemagglutinin on the M phi surface. After trypsin treatment fetal liver M phi recovered the ability to bind Eb and this process could be selectively inhibited by cycloheximide. Inhibition tests showed that the Eb receptor differs from known M phi plasma membrane receptors and fetal liver M phi did not bind sheep erythrocytes, a ligand for a distinct M phi hemagglutinin. We propose that fetal liver M phi interact with developing erythroid cells by a novel nonphagocytic surface hemagglutinin which is specific for a ligand found on Eb and not on mature red cells.
authors.affiliation: Sir William Dunn School of Pathology, University of Oxford, United Kingdom.
authors.forename: L
authors.initials: L
authors.lastname: Morris
authors.forename: P R
authors.initials: PR
authors.lastname: Crocker
authors.forename: S
authors.initials: S
authors.lastname: Gordon
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D002448:Cell Adhesion; D002478:Cells, Cultured; D003513:Cycloheximide / Q000494:pharmacology; D004900:Erythroblasts / Q000378:metabolism* / Q000648:ultrastructure; D005333:Fetus; D006388:Hemagglutinins / Q000378:metabolism*; D006410:Hematopoiesis; D008024:Ligands; D008099:Liver / Q000166:cytology* / Q000196:embryology; D008264:Macrophages / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D008274:Magnesium / Q000378:metabolism; D051379:Mice; D003012:Microbial Collagenase; D008855:Microscopy, Electron, Scanning; D014357:Trypsin / Q000494:pharmacology
chemical_list: D006388:Hemagglutinins; D008024:Ligands; D003513:Cycloheximide; D014357:Trypsin; D003012:Microbial Collagenase; D008274:Magnesium; D002118:Calcium