Inhomogeneity of the circulating BFU-E regulation in sickle cell anaemia: accessory cells properties and BFU-E growth factor response pattern.
Sickle cell anaemia (SS) patients with low (< 9%) HbF levels (LFSS) are characterized by an increased number of circulating BFU-E in active DNA synthesis, and release of burst promoting activity (BPA) by unstimulated low density (LD) adherent cells. In contrast, circulating BFU-E from SS patients with high (> 9%) HbF levels (HFSS) are normal in number, largely in resting phase, and their LD cells do not release BPA-like activity. We report now that in LFSS patients, adherent cell depletion decreases BFU-E growth in culture and apparent BFU-E cycling. Furthermore, addition of conditioned media (CM) from LD cells of LFSS patients restored cycling BFU-E expression in culture. Neutralization analysis with anti-GM-CSF antibody demonstrated that GM-CSF is, at least, one factor responsible for BPA activity present in this CM. Thus, GM-CSF is constitutively produced by unstimulated monocytes in LFSS patients. In contrast, HFSS patients' adherent cell depletion increases cycling of BFU-E in culture. CM from HFSS patients inhibits BFU-E expression in culture. Hence, LD adherent cells from HFSS patients may release a yet unknown inhibitor factor(s). In addition, we report a distinct response pattern in SS patients' BFU-E to growth factor (GM-CSF, IL-3): (a) LFSS patients have a BFU-E population, equally responsive to GM-CSF and IL-3; (b) HFSS patients, have a subset of BFU-E exclusively dependent on IL-3 (20-40% of the circulating BFU-E). This pattern is very similar to that of normal BFU-E. In conclusion, BFU-E from LFSS patients represent an actively proliferating population, equally responsive to GM-CSF and IL-3, controlled by constitutively produced GM-CSF, suggesting a unique BFU-E behaviour in SS patients with low HbF levels and high haemopoietic stress. The heterogeneous regulation of BFU-E in SS disease seems to be the epiphenomenon of HbF levels, and not vice versa.
Croizat
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Division of Hematology, Albert Einstein College of Medicine, Bronx, New York 10461.
Nagel
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D000328:Adult; D000755:Anemia, Sickle Cell / Q000097:blood*; D002448:Cell Adhesion / Q000502:physiology; D002478:Cells, Cultured; D003470:Culture Media; D004305:Dose-Response Relationship, Drug; D015672:Erythroid Precursor Cells / Q000187:drug effects / Q000473:pathology*; D005319:Fetal Hemoglobin / Q000032:analysis; D016178:Granulocyte-Macrophage Colony-Stimulating Factor / Q000276:immunology / Q000494:pharmacology*; D006801:Humans; D007106:Immune Sera; D007377:Interleukin-3 / Q000494:pharmacology*; D008875:Middle Aged; D011994:Recombinant Proteins / Q000494:pharmacology
D003470:Culture Media; D007106:Immune Sera; D007377:Interleukin-3; D011994:Recombinant Proteins; D016178:Granulocyte-Macrophage Colony-Stimulating Factor; D005319:Fetal Hemoglobin