Flow cytometric reticulocyte analysis. Multiinstitutional interlaboratory correlation study

Reticulocyte analysis by flow cytometry offers precision and sensitivity greater than those of conventional morphologic methods and permits derivation of a reticulocyte maturity index. However, interlaboratory variability has not yet been reported. The authors analyzed 310 samples at eight sites using 11 instruments over a 4-month period to examine intermethod and interlaboratory variabilities. Stains included thiazole orange, ethidium bromide, and auramine O. Instruments included models by Coulter, Becton Dickinson, TOA Medical Electronics, and Ortho Diagnostics. The coefficient of variation (CV) among all sites and methods on these samples varied as a function of the reticulocyte percentage, ranging from a mean CV of 69% for samples with < .5% reticulocytes to 24.1% for those with > 2.5% reticulocytes. The best performance was observed with the TOA R-1000 dedicated reticulocyte analyzers, with a mean CV of 18.4% for samples with < .5% reticulocytes and 4.6% for samples with > 2.5% reticulocytes. The reticulocyte maturity index showed comparable intersite precision, with a mean CV of 16% for samples with > 2.5% reticulocytes with multipurpose flow cytometers and a mean CV of 7.3% with the TOA R-1000 instruments. Interclass correlations among all sites ranged from .79 to .99 for the reticulocyte counts and .41 to .88 for the reticulocyte maturity index. The authors conclude that flow cytometric reticulocyte analysis is more precise than manual reticulocyte analysis. With greater automation of this methodology, further interlaboratory standardization of reticulocyte counts and the reticulocyte maturity index can be achieved.

Cyclic haemopoiesis at 7- or 8-day intervals

We report a patient with severe anaemia and cyclic oscillations of reticulocyte and leucocyte counts, as well as serum iron (Fe), unsaturated iron-binding capacity (UIBC), ferritin, C-reactive protein (CRP) levels and temperature, at regular intervals of 7 or 8 d. After treatment with prednisolone, anaemia was corrected and the cyclic oscillations of these parameters ceased; whereas treatment with indomethacin, recombinant granulocyte-colony stimulating factor (G-CSF) and erythropoietin (Epo) were unsuccessful.

Early detection of hematopoietic engraftment after bone marrow and peripheral blood stem cell transplantation by highly fluorescent reticulocyte counts

At present, the appearance of neutrophils in the peripheral blood is considered to be the earliest sign of hematopoietic regeneration after myeloablative chemoradiotherapy. We studied erythroid regeneration in 27 allogeneic and 21 autologous marrow recipients using an automated reticulocyte counter employing a flow cytometric technique. Thereby, reticulocytes can be divided into a high, moderate and low fluorescent fraction according to RNA content. Marrow ablation caused an immediate and rapid fall in highly fluorescent reticulocytes (HFR) to zero in all patients. HFR reappeared after a median time of 7 days after allogeneic and 11 days after autologous marrow grafting. This was 7 and 2 days earlier than the appearance of first neutrophils. In allogeneic marrow recipients given erythropoetin after marrow infusion the median time to reach HFR of 0.2 and 0.5 x 10(9)/l was significantly shorter than time to reach similar absolute neutrophil counts (ANC). In allogeneic marrow recipients treated with G-CSF time to rise of HFR and ANC was almost exactly the same. Thus, automated flow cytometric reticulocyte counting allows early detection of hematopoietic regeneration and may be of clinical value for the early diagnosis of inadequate marrow function after marrow transplantation and the monitoring of erythroid regeneration under cytokine administration.

Sequence analysis of cDNA derived from reticulocyte mRNAs coding for Rh polypeptides and demonstration of E/e and C/c polymorphisms

RNA derived from enriched reticulocytes of Rh-phenotyped donors was isolated, reversely transcribed into cDNA and amplified with Rh-specific primers by polymerase chain reaction. Nucleotide sequence analysis of the entire coding region of the Rh cDNAs was carried out. Four types of cDNAs were identified, tentatively designated as RhSCI, RhSCII, RhSCIII and RhSCIV. Comparison of RhSCII with RhSCI (identical to the previously reported RhIXb/30A cDNA), showed single base pair difference. Since RhSCI and RhSCII were found to be related to the presence of E or e antigen, respectively, the P226A amino acid polymorphism appears to be the genetic basis of the E/e polymorphism. RhSCIII was demonstrated to be a transcript derived from the RhD gene, with 35 amino acid substitutions as compared to RhSCI. RhSCIV was found to be present only in RhC-positive individuals, indicating that RhSCIV encodes a polypeptide carrying the C antigen. Six nucleotide changes, resulting in four amino acid substitutions W16C, L60I, N68S and P103S, were observed between RhSCII and RhSCIV, probably representing the C/c polymorphism.

Reticulocyte response to endogenous erythropoietin after renal transplantation

We determined in a prospective study reticulocyte counts and serum erythropoietin concentrations after renal transplantation in 37 recipients of renal allografts. Erythropoietin decreased in 35 patients out of 37 during surgery. Results concerning reticulocyte counts allowed us to define two groups of patients. Group 1: 33 patients had a reticulocyte peak before d29. Among them the reticulocyte peak followed the first Epo peak in 22 patients (1a) and occurred after several Epo peaks in 11 patients (1b). Patients of groups 1b had a serum creatinine level above 300 mumol/l at the time of the first Epo peak. Group 2: 4 patients with acute tubular necrosis had no reticulocytes peak before d29 despite one or several erythropoietin peaks. Post-operative erythropoietin reduction was not entirely explained by hemodilution or by per-operative blood transfusions. The erythropoietin peak appeared to be efficient only when creatinine at the time of the peak was under 200 mumol/l according to the inhibition of erythropoiesis during renal failure.

rh-erythropoietin stimulates immature reticulocyte release in man

The pharmacodynamics of single intravenous dosing with recombinant human erthropoietin (rhEPO) was investigated in eight healthy volunteers (150 U/kg, n = 2; 300 U/kg, n = 6) with respect to reticulocyte subdivisions (by fluorescence flow cytometry) and serum ferritin over 6.5 d. The present study shows that bolus rhEPO injection produces an immediate release of high and middle fluorescence (immature) reticulocytes with a high RNA content from the marrow into the circulation, whereas the low fluorescence (more mature) reticulocytes were at first not affected. Serum ferritin decreased markedly within 24 h, reaching a nadir 50% of baseline after 120 h (5 d), with no increase in haemoglobin. Our data suggests that rhEPO triggers premature expulsion of immature reticulocytes from the bone marrow into the circulation independent of its effect in stimulating erythropoiesis and that rhEPO has an effect on serum ferritin concentration which in this dynamic situation is dependent not only on the iron stores.

Role of membrane surface potential and other factors in the uptake of non-transferrin-bound iron by reticulocytes

Reticulocytes suspended in low ionic strength media such as isotonic sucrose solution efficiently take up non-transferrin-bound iron and utilize it for heme synthesis. The present study was undertaken to determine how such media facilitate iron utilization by the cells. The effects of changes in membrane surface potential, membrane permeability, cell size, transmembrane potential difference, oxidation state of the iron, and lipid peroxidation were investigated. Iron uptake to heme, cytosol, and stromal fractions of cells was measured using rabbit reticulocytes incubated with 59Fe-labelled Fe(II) in 0.27 M sucrose, pH 6.5. Suspension of the cells in sucrose led to increased membrane permeability, loss of intracellular K+, decreased cell size, and increased transmembrane potential difference. However, none of these changes could account for the high efficiency of iron uptake which was observed. The large negative membrane surface potential which occurs in sucrose was modified by the addition of mono-, di-, tri-, and polyvalent cations to the solution. This inhibited iron uptake to a degree which for many cations varied with their valency. Other cations (Mn2+, Co2+, Ni2+, Zn2+) were also very potent inhibitors, probably due to direct action on the transport process. Ferricyanide inhibited iron uptake, while ferrocyanide and ascorbate increased the uptake of Fe(III) but not Fe(II). It is concluded that the high negative surface potential of reticulocytes suspended in sucrose solution facilitates iron uptake by aiding the approach of iron to the transport site on the cell membrane. The iron is probably transported into the cell in the ferrous form.

[Patterns of erythropoietic reconstruction in the erythroblastic islands]

A decrease in the erythroid cell number in the erythroblastic island's crown seems to be an important factor for involvement of early erythroid cells in the contact with macrophages of maturing erythroblastic islands. The erythropoietin stimulation increases the affinity of these macrophages to the erythroid progenitor cells.

Estimation of effective and total erythropoiesis in myelodysplasia using serum transferrin receptor and erythropoietin concentrations, with automated reticulocyte parameters

The erythroid abnormality in patients with myelodysplasia (MDS) is multifactorial, with ineffective erythropoiesis and poor in vitro progenitor response to erythropoietin (EPO). Serum EPO concentration is variable among patients for a given haemoglobin concentration. We studied 19 non-transfusion-dependent patients with MDS, and 13 healthy elderly control subjects in an attempt to define the factors governing variability in serum EPO and to further characterise the anaemia of MDS. Serum EPO concentration was appropriate for the degree of anaemia in 15/19 MDS patients, and was positively related to mean cell volume (MCV), mean cell haemoglobin (MCH), and percentage highly fluorescent reticulocytes (% HFR), but not to absolute or percentage reticulocyte count. Although the observed/predicted ratio for serum transferrin receptor (TfR) concentration was low in 12 of 19 MDS subjects, no relationship to haemoglobin concentration, reticulocytes or serum EPO was seen. Serum TfR was positively correlated with WBC and platelet counts. Serum TfR was higher in patients with sideroblastic anaemia than refractory anaemia. Standardized in vivo p50 was positively correlated to red cell 2,3 diphosphoglycerate concentration, although this was not the only factor influencing the oxygen dissociation curve. We conclude that effective erythroid output responsive to endogenous EPO drive in MDS is positively related to MCV, MCH and % HFR. Serum TfR may not represent effective output as precisely as % HFR, but may be proportional to total marrow erythropoietic activity.

Cloning of human erythroid dematin reveals another member of the villin family

Dematin is an actin-bundling protein originally identified in the human erythroid membrane skeleton. Its actin-bundling activity is abolished upon phosphorylation by the cAMP-dependent protein kinase and is restored after dephosphorylation. Here we report the complete primary structure of human erythroid dematin, whose sequence includes a homologue of the "headpiece" sequence found at the C terminus of villin. This headpiece is essential for villin function in inducing microvillar development and actin redistribution. The widespread expression of dematin transcripts in human tissues suggests that dematin and its homologues may substitute for villin in villin-negative tissues to regulate actin reorganization by a phosphorylation-regulated mechanism.

Molecular analysis of glycophorin C deficiency in human erythrocytes

Human erythrocyte glycophorin C plays a functionally important role in maintaining erythrocyte shape and regulating membrane mechanical stability. We report here the characterization of the glycophorins C and D deficiency in erythrocytes of the Leach phenotype. Glycophorin C gene is encoded by 4 exons. Amplification of reticulocyte cDNA from Leach phenotype and normal individuals generated a 140-bp fragment when using primers spanning exons 1 and 2. However, no polymerase chain reaction (PCR) products were detected in the Leach phenotype using primers flanking either exons 1 and 3 or exons 1 and 4, suggesting that the 3' end of the mRNA was missing or altered. Exon 4 also appeared to be missing from Leach genomic DNA, based on both Southern hybridization and PCR. These results indicate that an absence of glycophorin C and glycophorin D in erythrocytes from these Leach phenotype individuals is a consequence of a deletion or marked alteration of exon 3 and exon 4 of their glycophorin C gene. Surprisingly, the mutant gene encodes an mRNA stable enough to be detected in circulating reticulocytes. Although this mRNA could encode an N-terminal fragment of glycophorin C, these protein isoform(s) would not be expressed in the membrane because they lack the transmembrane and cytoplasmic domains.

Complex patterns of sequence variation and multiple 5' and 3' ends are found among transcripts of the erythroid ankyrin gene

The structural protein ankyrin functions in red blood cells to link the spectrin-based membrane skeleton to the plasma membrane. Ankyrin proteins are now known to occur in most cell types, and two distinct ankyrin genes have been identified (erythroid (Ank-1) and brain (Ank-2)). We have characterized transcripts of the mouse erythroid ankyrin gene by cDNA cloning and DNA sequencing. Ank-1 transcripts of 7.5 and 9.0 kilobases are found in erythroid tissues, and a 9.0-kilobase transcript is found in cerebellum. RNA hybridization blot analysis of 13 additional mouse tissues has detected four novel Ank-1 transcripts (5.0, 3.5, 2.0, and 1.6 kilobases in size). Sequencing of Ank-1 cDNA clones isolated from mouse reticulocyte, spleen, and cerebellar libraries has identified (i) multiple 5' ends that indicate possible multiple promoters; (ii) alternative polyadenylation sites that probably account for the 7.5- and 9.0-kilobase size difference; (iii) a variety of small insertions and deletions that could produce transcripts (and ultimately proteins) of nearly identical size, but different functions; and (iv) clones with large deletions of coding sequence that account for the smaller transcripts seen in spleen, skeletal muscle, and heart.

Flow cytometric reticulocyte analysis and the reticulocyte maturity index

Reticulocyte analysis has evolved to one of the accepted and routinely practiced clinical applications of flow cytometry technology. Similar to CD4 measurements, FCM technology has contributed to documented improvements in reticulocyte counting precision over previous microscope-based techniques. The ability to FCM instruments to quantitate fluorescence intensity has been utilized to derive a parameter of reticulocyte maturity, which we have termed the reticulocyte maturity index. The FCM-derived RMI parameter offers an additional perspective to assess the erythropoietic response in anemic patients over reticulocyte counting alone and provides further insight into the differential diagnosis of anemia. Clinical utility of the RMI has been reported in monitoring expensive, new-technology therapies, such as bone marrow transplantation and erythropoietin therapy. FCM reticulocyte analysis is still not fully mature, but is in a state of continued evolution. Needs exist for (i) improved software for data analysis, (ii) newer automation techniques to improve interlaboratory correlations, and (iii) further validation and refinement of the reticulocyte maturity index parameter.

Differentiation-associated switches in protein 4.1 expression. Synthesis of multiple structural isoforms during normal human erythropoiesis

Erythroid differentiation is accompanied by dramatic alterations in morphology and membrane mechanical properties resulting, in large part, from reorganization of the membrane skeletal protein network. The 80-kD protein 4.1 is an important organizational component of this membrane skeleton. Recently, it has been recognized that multiple structural isoforms of 4.1 are encoded by a single gene via alternative pre-mRNA splicing, and that an upstream ATG can be spliced in and used for translation of high molecular weight 4.1. We are exploring the hypothesis that differentiation-associated switches in protein 4.1 structure play an important role in membrane reorganization. To study changes in 4.1 gene expression during normal human differentiation, we analyzed 4.1 protein and mRNA structure at various developmental stages. Using immunofluorescence microscopy, we observed high molecular weight 4.1 isoforms in preproerythroblasts producing punctate, predominantly cytoplasmic staining with a perinuclear area of intense fluorescence, while mature red cells expressed very little high molecular weight 4.1. Isoforms containing an alternatively expressed 102-nucleotide exon near the COOH terminus were abundant in both preproerythroblasts and mature cells but produced a punctate distribution of fluorescence over the entire preproerythroblast and intense membrane-associated fluorescence in the erythrocyte. Characterization of RNA by polymerase chain reaction and nuclease protection assays revealed a differentiation-associated switch in pre-mRNA splicing in the spectrin-actin binding domain. Since this domain plays a critical role in regulating membrane material properties, we speculate that this switch may be crucial to reorganization of the skeletal network during erythropoiesis. We conclude that 4.1 isoforms are differentially expressed and differentially localized during erythropoiesis, and that this isoform family is likely to have diverse functions during terminal differentiation.

[Kinetics of erythropoietin blood levels from D-1 to D-29 in kidney transplantation]

This study of serum erythropoietin levels and reticulocytes counts in the first month after kidney transplantation shows that the erythropoietin peak is efficient only when serum creatinine level at the time of the peak is under 200 mumol/l.

Thrombospondin mediates adherence of CD36+ sickle reticulocytes to endothelial cells

Initiation of vasocclusion in sickle disease pathophysiology may involve abnormal red blood cell (RBC) adhesivity to endothelium, a phenomenon influenced by both RBC and plasma factors. Using human umbilical vein endothelial cells and a gravity sedimentation adherence assay, we have examined thrombospondin (TSP) as a plasma factor in this adhesive event. The already-abnormal adherence of sickle RBCs in buffer/albumin is significantly augmented (P < .001) by the addition of TSP, with half-maximal effect at about 0.3 microgram/mL. This effect is abolished by antibodies to either TSP or glycoprotein (GP) IV (CD36), as well as peptides RGDS and CSVTCG. The even greater adherence (P < .005) of sickle RBCs in autologous platelet-rich plasma (without added TSP) is dramatically inhibited by alpha CD36 antibodies (OKM5 and alpha GPIV) and significantly diminished by alpha TSP, by peptides RGDS and CSVTCG, and by two antibodies to the vitronectin receptor (7E3 and LM609). Studies of density-separated subpopulations and of RBC adhesion to immobilized proteins, as well as analysis of sickle RBCs using fluorescence-activated cell sorting and single cell microfluorometry, show that TSP responsiveness is a feature of the immature sickle "stress" reticulocytes, which carry CD36 (and not GPIIbIIIa-like receptors) as the TSP-receptive moiety. The endothelial cell's participation in this phenomenon appears to be more complex, and the data are consistent with the notion that it involves TSP interaction with other plasma proteins and/or multiple receptor structures. Other potential adhesogenic proteins (plasma von Willebrand factor, vitronectin, fibrinogen, and fibronectin) neither exhibited an affinity for reticulocytes nor supported increased sickle RBC adherence when added to buffer/albumin in these assay systems. In aggregate, our results indicate that TSP may be the major promoter of RBC adhesivity in plasma, and they suggest that therapeutic benefit might derive from interference with sickle reticulocyte CD36, as achieved by antibodies and CSVTCG in these studies.

Characteristics of phosphorylated and non-phosphorylated dentine phosphoprotein

Heterogeneity among the odontoblast-specific, highly phosphorylated acidic protein dentine phosphoprotein (DPP) obtained from different species has been reported by several investigators. In the present study, the apparent molecular-mass variations in rabbit and mouse DPP were investigated. Extracellular matrix (ECM) DPPs were isolated and characterized. Primary gene products, before post-translational phosphorylation, were analysed based upon translation products produced in a rabbit reticulocyte lysate cell-free system using a polyclonal mouse anti-DPP antibody. Nascent non-phosphorylated DPPs were also identified from intracellular protein extracts. Mouse and rabbit ECM phosphoproteins exhibited a 10 kDa difference in size. However, nascent intracellular or translation products from both species showed the same lower molecular mass (approx. 45 kDa). Furthermore, Northern-blot analysis showed a single mRNA of the same size in both species (approx. 1.6 kb) which contains information for a protein no larger than 50 kDa. Our results indicate that the difference in molecular mass (or electrophoretic behaviour) among DPPs from different species is due to post-translational modifications, in this case phosphorylation.

Cyclosporine and prednisone therapy for pure red cell aplasia in patients with chronic lymphocytic leukemia

We describe the characteristics of response to treatment with cyclosporine (CYA) plus prednisone in seven episodes of pure red cell aplasia (PRCA) in four patients with B cell chronic lymphocytic leukemia (CLL). Fourteen episodes of PRCA occurred in four patients with CLL. Eleven episodes were treated with conventional therapies which included an alkylating agent and prednisone. Four episodes that failed to respond to conventional therapies and an additional three episodes were treated with CYA and prednisone. Six of the seven episodes, including three of four which had failed conventional therapies, responded to CYA plus prednisone compared with six of eleven episodes treated with conventional therapies. Response to CYA and prednisone occurred without a reduction in leukemic mass. In contrast, PRCA remission did not occur until after leukemic mass reduction in three of four patients treated successfully with conventional therapies. Time to response was shorter (14 +/- 3 days) with CYA plus prednisone than with conventional therapies (154 +/- 97 days) in three of four patients. These results indicate that CYA plus prednisone is an effective therapy for the induction of remission from PRCA in patients with CLL.

Parathyroid stimulation after bleeding in man

A role for the PTH-calcium axis in the normal bone-marrow response to bleeding or erythropoietin administration has been demonstrated in rats. We studied 20 autologous blood donors, each donating two units of blood, who served as a human bleeding model. Fifteen patients completed the study. Blood donations were followed by a significant increase in serum intact PTH (2.15 +/- 0.67 to 2.81 +/- 0.84 pmol/l; p = 0.0003) and protein-corrected total calcium (2.43 +/- 0.09 to 2.49 +/- 0.08 mmol/l; p = 0.2). All the individual values remained within the normal range. PTH weakly correlated with the reticulocyte count, but not with the corrected serum calcium. We conclude that moderate bleeding in humans is followed by a physiological increase in serum PTH and calcium.

Neonatal erythropoiesis. I. Peripheral blood erythropoietic parameters: data suggest erythropoietin transfer via maternal milk

In this study peripheral blood erythropoietic parameters in 9 to 12-day-old neonatal rats suckled by experimentally-induced anemic mothers were examined. Stimulation of erythropoiesis in these pups was judged by increases in hematocrit, hemoglobin, mean corpuscular hemoglobin and mean corpuscular hemoglobin concentration. Failure to observe increases in reticulocytes may be, in part, the result of decreased maturation time, as indicated by reticulocyte Heilmeyer maturation indices in peripheral blood. The reticulocyte maturation curve was shifted to the left in neonates nursing from anemic mothers. These results suggest that erythropoietin (Ep) is transmitted to suckling rats via maternal milk, and by escaping inactivation in their gastrointestinal tract stimulates their erythropoiesis. These findings, in agreement with our previous work, are supportive of studies by others and further indicate a maternal-neonatal erythropoietic relation in rats.

Evaluation of erythropoiesis after bone marrow transplantation: quantitative reticulocyte counting

Erythroid regeneration is an important and separate element in the engraftment process in allogeneic and autologous bone marrow transplantation (alloBMT, autoBMT). Qualitative visual reticulocyte counting has proved inadequate in the evaluation of erythropoiesis after BMT but automated flow cytometry now allows the reliable quantitation of reticulocytes even to very low levels. Reticulocyte counts and highly fluorescent reticulocyte (HFR) counts (very early reticulocytes) were estimated daily in recipients of 22 autoBMT and 14 alloBMT using a Sysmex R-1000 automated reticulocyte counter. Marrow ablation caused an immediate and rapid fall in both the reticulocyte count and the HFR. Measurable numbers of reticulocytes persisted throughout the hypoplastic period, but HFR fell to zero in the majority of both the autoBMT and alloBMT. HFR rose significantly after a median time of 14 d post-autoBMT, and 12 d post-alloBMT. Attainment of 15 x 10(9)/l reticulocytes and 0.5 x 10(9)/l HFR at day 21 post-transplant was associated with ultimate engraftment in 100% cases. Inadequate engraftment was seen in the majority of patients whose responses fell below these levels. Graft-versus-host disease was associated with a transient slight reduction in reticulocyte count. Neither episodes of infection nor blood transfusions had any significant impact on trends of reticulocytes or HFR. Automated flow cytometric reticulocyte counting has been shown to provide an accessible measure of erythroid activity which may be of predictive value in the management of patients following bone marrow transplantation.

Kinetics of erythrogenesis after bone marrow transplantation

To determine the kinetics of bone marrow erythrogenesis after bone marrow transplantation, the authors counted reticulocytes (by blood smear and flow cytometry) and compared those data with neutrophil and platelet recovery in 23 consecutive bone marrow transplant patients. The earliest indication of marrow recovery after allogeneic and autologous bone marrow transplantation was defined as the second increasing cell count after the lowest recorded count, provided that the trend continued upward. Recovery of marrow function was detected earlier in 10 of 23 patients using reticulocyte counts than by either neutrophil or platelet count alone. Specifically, in 8 of these 10 patients, recovery of erythropoiesis was determined earlier by flow cytometric examination than by the blood smear method. On the other hand, combining the data using the earliest value of platelet, neutrophil, and reticulocyte counts indicated that the mean day of recovery in our patient population was determined to be 12.1 +/- 4 days after marrow infusion. In patients undergoing autologous and allogeneic bone marrow transplantation, serial neutrophil and reticulocyte count determinations are complementary in early clinical detection of successful engraftment.

Application of 67Ga for the estimation of reticulocyte production

In order to estimate the production of reticulocytes, which have a larger number of transferrin receptors than erythrocytes, we used 67Ga which is exclusively bound to transferrin in the blood. The pattern of uptake of 67Ga by reticulocytes was quite similar to the time course of transglutaminase activity which might be involved in receptor-mediated endocytosis. The preinjection of Fe3+ decreased the uptake of 67Ga by reticulocytes. These results suggested that 67Ga in a transferrin-bound form was taken up by reticulocytes via receptor-mediated endocytosis. It was showed that the application of 67Ga is very easy and useful for the estimation of reticulocyte production.

Rapid molecular diagnosis of hemoglobin variants by RT-PCR of reticulocyte mRNA and direct sequencing

We have developed a rapid and simple approach for the molecular characterization of hemoglobin variants by a one-step reverse transcription-polymerase chain reaction of reticulocyte mRNA and direct sequencing of the product. This method can selectively amplify the alpha 1- or alpha 2-globin gene or the beta-globin gene transcript. The amino acid substitution of Hb G-Taichung is due to a G----C mutation at codon 74 of the alpha 1-globin gene, that of Hb J-Meinung to a G----A substitution at codon 56 of the beta-globin gene, and that of Hb Kaohsiung (or New York) to a T----A substitution at codon 113 of the beta-globin gene. The amplified segment encompassed the sequence from upstream of the initial codon behind the Cap site to downstream of the terminal codon before the polyadenylation addition signal. Hence, all hemoglobin variants should be able to be characterized by this approach.

Uptake of transferrin-bound and nontransferrin-bound iron by reticulocytes from the Belgrade laboratory rat: comparison with Wistar rat transferrin and reticulocytes

The mechanism underlying the impaired uptake of iron from transferrin by reticulocytes from the Belgrade laboratory rat was investigated using 125I- and 59Fe-labeled transferrin isolated from homozygous Belgrade rats and from Wistar rats, nontransferrin-bound Fe(II) in an isotonic sucrose solution, and reticulocytes from Belgrade and Wistar rats. The Belgrade rat transferrin had the same molecular weight and net charge as Wistar rat transferrin, donated iron equally well to both types of reticulocytes, and competed equally for transferrin binding sites on the cells. Hence, the defect in iron uptake by Belgrade rat reticulocytes could not be attributed to an abnormality of the transferrin molecule. The rate of uptake of Fe(II) from sucrose into the cytosolic and stromal fractions of Belgrade rat reticulocytes was only about 35% as great as that by Wistar rat reticulocytes. With both types of cells, the uptake process was saturable, suggesting the presence of a carrier-mediated process. It was therefore concluded that the defect in iron uptake by Belgrade rat erythroid cells is probably the consequence of a deficiency in a membrane carrier for iron.