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G Zauli, L Valvassori and S Capitani
Institute of Human Anatomy, University of Ferrara, Italy.
The in vitro growth of early (burst-forming unit-megakaryocyte [BFU- meg])
and late (colony-forming unit-megakaryocyte [CFU-meg]) megakaryocyte
progenitors was investigated in midtrimester human fetal blood and compared
with adult bone marrow. Most of the experiments were performed in a
serum-free fibrin-clot assay, using purified hematopoietic progenitor
(CD34+) cells. High BFU-meg and CFU-meg levels were found in human fetal
blood, with a clear prevalence of BFU-meg (BFU-meg:CFU-meg ratio, 2.5:1),
at variance with adult bone marrow, in which mature CFU-meg predominate
(BFU-meg:CFU-meg ratio, 0.6:1). Fetal and adult megakaryocyte progenitors
had a similar phenotypic profile for the expression of CD34, HLA-DR, and
glycoprotein-complex IIB-IIIA. However, fetal BFU-meg were larger in size
(number of megakaryocytic elements per colony) than adult BFU-meg, but were
usually composed by only one or two foci of development. On the other hand,
fetal and adult CFU-meg were similar in both morphology and size. Fetal
megakaryocyte progenitors appeared earlier in culture and had an increased
proliferative activity as demonstrated by the higher number of
megakaryocyte progenitors in S phase with respect to adult CFU-meg and
BFU-meg. Finally, fetal megakaryocyte progenitors displayed a higher
sensitivity to stimulatory cytokines, in particular recombinant
interleukin-3, than adult megakaryocyte progenitors, whereas they were
inhibited by purified transforming growth factor-beta 1 in a similar
fashion to adult megakaryocyte progenitors.
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| Copyright © 1993 by American Society of Hematology Online ISSN: 1528-0020 | |||||||||