Barrier cells: stromal regulation of hematopoiesis and blood cell release
in normal and stressed murine bone marrow
L Weiss and U Geduldig
Laboratory of Experimental Hematology and Cell Biology, School of
Veterinary Medicine, University of Pennsylvania, Philadelphia 19104- 6046.
Murine hematopoietic bone marrow is heterogenous in respect to bone- lining
cells, hematopoiesis, and release of blood cells. In diaphyseal femoral
marrow, bone-lining cells are largely osteoblasts, indifferent endosteum,
blood cells, and reticular cells. Hematopoiesis is sustained by rather
differentiated progenitors, as myelocytes and polychromatophilic
erythroblasts. But in sharply restricted loci within trabeculated bone in
the distal medial femoral metaphysis, bone-lining cells are dominated by
newly discovered fibroblastic, contractile, stromal barrier cells;
activated, multilaminar and branched, enveloping putative stem cells; and
extending into the marrow, where they enclose hematopoietic clusters of
rather early progenitors, as promyelocytes; and basophilic erythroblasts.
Barrier cells may endocytize granules released individually by vicinal
differentiating granulocytes, preventing tissue damage. Barrier cells
envelope blood vessels and insinuate processes into their wall, augmenting
blood-marrow barriers, preventing release of immature cells. Further,
extensions of venous sinuses made of extraordinarily thin barrier cell
processes receive released blood cells. With heightened hematopoiesis due
to mutant hemolytic anemias or after administration of interleukin-1,
barrier cells and their associated structures are greatly increased,
spreading beyond normally restricted loci. But in
microenvironment-deficient mutants, barrier cells are fewer, less
activated, and less granulated. Barrier cells thus appear important in
hematopoiesis and in the release of blood cells from bone marrow.
Volume 78,
Issue 4,
pp. 975-990,
08/15/1991
Copyright © 1991 by The American Society of Hematology
