An evaluation of the effects of a recombinant, soluble form of the c-kitligand alone and in combination with either granulocyte-macrophage colony-stimulating factor (GM-CSF) or interleukin-3 (IL-3) ...on the regulation of human megakaryocytopoiesis was performed using a serum-depleted clonal assay system and a long-term bone marrow culture system. The effects of thec-kitligand on the primitive megakaryocyte (MK) progenitor cell, the burst-forming unit-megakaryocyte (BFU-MK), and the more differentiated colony-forming unit-megakaryocyte (CFU-MK) were determined. Thec-kitligand alone had no megakaryocyte colony-stimulating activity (MK-CSA) but was capable of augmenting the MK-CSA of both GM-CSF and IL-3. The range of synergistic interactions ofc-kitligand varied with the class of MK progenitor cell assayed. In the case of the BFU-MK, thec-kitligand synergistically augmented the numbers of colonies formed in the presence of IL-3, but not GM-CSF, but increased the size of BFU-MK–derived colonies cloned in the presence of both of these cytokines. However, at the level of the CFU-MK,c-kitligand synergized with both GM-CSF and IL-3 by increasing both colony numbers and size. Although thec-kitligand alone exhibited limited potential in sustaining long-term megakaryocytopoiesis in vitro, it syngeristically augmented the ability of IL-3, but not GM-CSF, to promote long-term megakaryocytopoiesis. These data indicate that multiple cytokines are necessary to optimally stimulate the proliferation of both classes of MK progenitor cells and that thec-kit ligand plays a significant role in this process by amplifying the MK-CSA of both GM-CSF and IL-3.
Parvovirus B19 infection leads to transient aplastic crises in individuals with chronic hemolytic anemias or immunodeficiency states. An additional unexplained sequela of B19 infection is ...thrombocytopenia. Because B19 is known to have a remarkable tropism for human erythropoietic elements, and is not known to replicate in nonerythroid cells, the etiology of this thrombocytopenia is uncertain. We sought to define the pathobiology of B19-associated thrombocytopenia by examining the role of B19 on in vitro megakaryocytopoiesis. B19 infection of normal human bone marrow cells significantly suppressed megakaryocyte (MK) colony formation compared with mock-infected cells. No such inhibition was observed with a nonpathogenic human parvovirus, the adeno-associated virus 2 (AAV). The B19-MK cell interaction was also studied at the molecular level. Whereas low-density bone marrow cells containing erythroid precursor cells supported B19 DNA replication, no viral DNA replication was observed in B19-infected MK-enriched fractions as determined by the presence of viral DNA replicative intermediates on Southern blots. However, analysis of total cytoplasmic RNA isolated from B19-infected MK fractions showed a low-level expression of the B19 genome as detected by quantitative RNA dot blots as well as by Northern analysis. Furthermore, a frame-shift mutation in a recombinant AAV-B19 hybrid genome segment that encodes the viral nonstructural (NS1) protein significantly reduced the observed inhibition of MK colony formation. These studies indicate tissue-tropism of B19 beyond the erythroid progenitor cell, and lend support to the hypothesis that B19 genome expression may be toxic to cell populations that are nonpermissive for viral DNA replication.
Human marrow cells positive for the CD34 antigen but not expressing HLA-DR, CD15, or CD71 antigens were isolated. In a liquid culture system supplemented with 48-hourly additions of recombinant ...interleukins IL-1 alpha, IL-3, IL-6, or granulocyte/macrophage colony-stimulating factor (GM-CSF), these cells were capable of sustaining in vitro hematopoiesis for up to eight weeks. The establishment of an adherent cell layer was never observed. Cultures containing no exogenous cytokine produced clonogenic cells for only 1 wk. IL-1 alpha and IL-6 were alone able to support hematopoiesis for 2 or 3 wk. Cells maintained with GM-CSF proliferated and contained assayable colony-forming cells for 3 or 4 wk, while maximal cellular expansion and generation of assayable progenitor cells occurred in the presence of IL-3 for 4-5 wk. When IL-3 was combined with IL-1 alpha or IL-6, hematopoiesis was sustained for 8 wks. Basophil numbers were markedly increased in the presence of IL-3. These studies indicate that marrow subpopulations can sustain hematopoiesis in vitro in the presence of repeated additions of cytokines. We conclude that a major function of marrow adherent cells in long-term cultures is that of providing cytokines which promote the proliferation and differentiation of primitive hematopoietic cells.
We have previously reported the ability of uncharacterized human bone marrow (BM) cells to engraft into preimmune fetal sheep, thereby creating sheep-human chimera suitable for in vivo examination of ...the properties of human hematopoietic stem cells (HSC). Adult human bone marrow CD34+ HLA-DR– cells have been extensively characterized in vitro and have been demonstrated to contain a number of primitive hematopoietic progenitor cells (PHPC). However, the capacity of such highly purified populations of human marrow CD34+ HLA-DR– cells to undergo in vivo self-renewal and multipotential lymphohematopoietic differentiation has not been previously demonstrated. To achieve that, human CD34+ HLA-DR– cells were transplanted in utero into immunoincompetent fetal sheep to investigate the BM-populating potential of these cells. Long-term chimerism, sustained human hematopoiesis, and expression of human cells belonging to all human blood cell lineages were demonstrated in two animals for more than 7 months' posttransplantation. Chimeric BM contained erythroid, granulocytic/monocytic, and megakaryocytic hematopoietic progenitor cells, as well as the primitive high proliferative potential colony-forming cell (HPP-CFC). Under a variety of in vitro experimental conditions, chimeric BM cells gave rise to human T cells expressing T-lymphocyte–specific markers, human natural killer (NK) cells, and human IgG-producing B cells. In vivo expansion and possibly self-renewal of transplanted PHPC was confirmed by the detection in chimeric BM 130 days' posttransplantation of CD34+ HLA-DR– cells, the phenotype of human cells constituting the stem-cell graft. These studies demonstrate not only the BM-populating capacity, multipotential differentiation, and most likely self-renewal capabilities of human CD34+ HLA-DR– cells, but also that this BM population contains human HSC. Furthermore, it appears that this animal model of xenogeneic stem-cell transplantation is extremely useful for in vivo examination of human hematopoiesis and the behavioral and functional characteristics of human HSC.
Two patients with sideroblastic anemia secondary to zinc-induced copper deficiency absorbed excess zinc secondary to oral ingestion. The source of excess zinc was a zinc supplement in one case; in ...the other, ingested coins. In each case, the sideroblastic anemia was corrected promptly after removal of the source of excess zinc. These two cases emphasize the importance of recognizing this clinical entity, since the myelodysplastic features are completely reversible.
The SHP-1 phosphatase associates with the receptors for erythropoietin, stem cell factor, and interleukin-3, and negatively regulates the mitogenic signals generated during engagement by their ...respective ligands. The erythroid progenitors of patients with polycythemia vera are hypersensitive to the mitogenic effects of these growth factors despite the fact that the numbers and binding affinities for their receptors are not increased. To determine whether post-receptor signaling defects may account for growth factor-hypersensitivity in polycythemia vera, we determined the expression of SHP-1 in highly purified erythroid progenitors from polycythemia vera patients. Our data demonstrate that in approximately 60% of the patients, expression of SHP-1 in the colony forming unit-erythroid population is diminished. The decreased expression of the protein may result from a transcriptional defect, as suggested by the diminished SHP-1 mRNA expression in the erythroid progenitors of these patients. Studies to determine the level of maturation of polycythemia vera and normal cells indicated that there was no difference between the two at early colony forming unit-erythroid stage of differentiation although polycythemia vera cells showed retarded differentiation kinetics at late colony forming unit-erythroid stage of differentiation. Furthermore, SHP-1 expression in normal colony forming unit-erythroid demonstrated downregulation of mRNA and protein levels during terminal differentiation, suggesting that its function is required for growth control during the early stages of erythropoiesis. These results indicate an important role for SHP-1 in the regulation of normal human erythroid progenitors and suggest that defective expression of the protein may contribute to the pathogenesis of polycythemia vera.
Early cochlear implantation is desirable to effect maximal development of receptive and expressive language. Factors to consider in implanting before the age of 2 years include anatomic ...considerations, temporal bone growth and device extrusion or migration, the sequela of otitis media, and the accuracy of early diagnosis. Clinical experience and laboratory data indicate that cochlear implantation before the age of 2 years is possible.
Otosclerosis Hoffman, Ronald
The Volta review,
1997, Letnik:
99, Številka:
5
Journal Article
Recenzirano
This article discusses otosclerosis, a metabolic bone disease affecting the bones of the ear, but no other bones in the human body. It explains that otosclerosis results in progressive hearing loss ...that begins in the late twenties or early thirties and can be treated successfully with hearing aids or surgery. (Author/CR)
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, OILJ, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK, VSZLJ
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