Specific antibodies to human fetal hemoglobin were prepared and, after conjugation with a fluorescent dye, were used to determine the distribution of Hb F-containing cells in blood smears from normal adults and individuals with hereditary and acquired conditions associated with abnormal levels of Hb F. The mean proportion of F-cells in normal persons was 2.7% +/- 1.4%, with a range of 0.5%-7.0%. Proportions of F-cells were increased in persons with several acquired and inherited disorders that are associated with an increased percentage of Hb F in hemolysates. A strong linear correlation between the amount of Hb F and proportion of F-cells was observed. This technique may prove useful in studies of a variety of disorders associated with Hb F elevations and also in investigations of the mechanisms controlling the transition from fetal to adult hemoglobin during the course of human development.
A new form of hereditary persistence of fetal hemoglobin (HPFH) producing 3%-8% Hb F in heterozygotes and an elevation of F-cell counts as measured by both the Kleihauer test and an antibody fluorescent procedure was found during the study of a black family. Individuals with this anomaly also had sickle cell trait. A sickle cell homozygote who had apparently inherited the HPFH determinant had 20.3% Hb F. Both types of gamma-chains were present in equal proportions in the Hb F of these individuals. A population study revealed other AS individuals with increased Hb F synthesis, three of whom were sibs. The presence of this previously unrecognized form of HPFH might explain the mild clinical manifestations and the hemoglobin phenotypes of sickle cell homozygotes with unusual elevations of Hb F.
The production of fetal hemoglobin was investigated in plasma clot cultures of adult bone marrow cells from normal donors and from individuals with homozygous HbS or HbC disease. Synthesis of gamma and beta chains was assessed either by 35S-methionine labeling of cultures and measurement of the radioactivity incorporated into the methionine- containing tryptic peptides of the gamma and beta subunits or by 3H- leucine labeling and measurement of the radioactivity incorporated into the globin chains of Hbs F0 and A0 isolated by ion-exchange chromatography. The cultures from all individuals responded with increased production of HbF. Cultured cells from subjects without a hemoglobinopathy produced an average of 8.2% gamma chains (range 3.1%– 20.3%), while cultured cells from subjects homozygous for HbS or HbC produced an average of 16.6% gamma chains (range 12.2%–20.4%). These findings indicate that fetal Hb production was regularly enhanced in adult bone marrow cells triggered in vitro to clonal growth in the plasma clot culture system.
Six monoclonal antibodies specific for human globin chains are described. They are produced by stable clones obtained by raising hybridomas using cells of mice immunized with either adult or fetal hemoglobin. Characterization of the antibodies included testing against tetrameric human and other animal hemoglobins, isolated hemoglobin chains, and when indicated, cyanogen bromide fragments. Monoclonals 16- 2 and 37–8 are beta-chain specific. Antibody 31–2 recognizes an antigenic determinant common to the alpha and beta subunits. Monoclonal 30–3 recognizes determinants best expressed in the alpha 2 beta 2 tetramer. Antibody 45–1 recognizes a determinant common to beta and gamma subunits, while antibody 51–7 is gamma-chain specific. None of the monoclonal antibodies recognizes mouse hemoglobin, and they display significant differences in binding to hemoglobins of various species. The species-specific reactions and the knowledge of the primary structures of globins allowed deductions about the antigenic sites recognized by two of the monoclonals (16–2 and 45–1). These antihemoglobin monoclonal antibodies will provide useful probes for studying hemoglobin expression in vivo and in vitro.
Fetal hemoglobin was studied in endogenous colonies produced in plasma clot and methylcellulose cultures of circulating progenitors from patients with polycythemia vera (PV). Analysis of globin chain synthesis showed that gamma chains constituted from 13% to 42% of the non-alpha chains produced in cultured cells, whereas from 27% to over 50% of the endogenous colonies contained Hb F, as indicated by the fluorescent antibody probe. Since the endogenous colonies in PV cultures originate from the abnormal PV clone, the findings provide direct evidence that a single pluripotent stem cell can have committed progeny that differ in their expressions of the Hb F production program.
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