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.

Effect of iron status on reticulocyte mean channel fluorescence

Flow cytometric reticulocyte enumeration measures the fluorescence intensity of the reticulocyte population, the reticulocyte mean channel fluorescence. Reticulocyte mean channel fluorescence, used as an indicator of reticulocyte maturation, is directly proportional to the amount of intracellular RNA. Other factors, such as iron stores, may affect reticulocyte mean channel fluorescence. Iron status in normal controls, patients with anemia of chronic disease, and pregnant women was evaluated by hemoglobin, hematocrit, red blood cell indices, iron, total iron-binding capacity, and ferritin. Reticulocyte mean channel fluorescence was significantly elevated (P less than 0.0001) to 85.6 +/- 4.6 (mean +/- 1 standard deviation) in iron-deficient anemic patients and to 81.1 +/- 8.4 in iron-depleted patients compared to healthy individuals (69.7 +/- 2.6). The reticulocyte mean channel fluorescence in anemia of chronic disease was 71.3 +/- 5.8 and was not significantly different from that of normal controls. Reticulocyte mean channel fluorescence showed significant correlations with total iron-binding capacity (P less than 0.0001, r = 0.62) and ferritin (P less than 0.0001, r = 0.40). A possible explanation for these findings, describing differences in cytoplasmic levels of transferrin receptor mRNA, is discussed.

Deletion in erythrocyte band 3 gene in malaria-resistant Southeast Asian ovalocytosis

Southeast Asian ovalocytosis (SAO) is a hereditary condition that is widespread in parts of Southeast Asia. The ovalocytic erythrocytes are rigid and resistant to invasion by various malarial parasites. We have previously found that the underlying defect in SAO involves band 3 protein, the major transmembrane protein, which has abnormal structure and function. We now report two linked mutations in the erythrocyte band 3 gene in SAO: (i) a deletion of codons 400-408 and (ii) a substitution, A----G, in the first base of codon 56 leading to substitution of Lys-56 by Glu-56. The first defect leads to a deletion of nine amino acids in the boundary of cytoplasmic and membrane domains of band 3. This defect has been detected in all 30 ovalocytic subjects from Malaysia, the Philippines, and two unrelated coastal regions of Papua New Guinea, whereas it was absent in all 30 controls from Southeast Asia and 20 subjects of different ethnic origin from the United States. The Lys-56----Glu substitution has likewise been found in all SAO subjects. However, it has also been detected in 5 of the 50 control subjects, suggesting that it represents a linked polymorphism. We conclude that the deletion of codons 400-408 in the band 3 gene constitutes the underlying molecular defect in SAO.

Reticulocyte rigidity and passage through endothelial-like pores

The importance of cell rigidity in regulating the release of reticulocytes from the bone marrow has been investigated in a model system. Reticulocytes were obtained from phlebotomized rabbits and separated from whole blood by discontinuous density gradient centrifugation. The mechanical properties of the cells were tested. Using single-cell micromechanical techniques, the membrane elastic rigidity and the viscoelastic response of reticulocyte and mature cell populations were measured. The reticulocyte membranes were more rigid than the mature membranes, but the reticulocyte properties were heterogeneous, and some cells exhibited behavior indistinguishable from the mature cells. The mean time constant for viscoelastic recovery was the same for reticulocytes as for mature cells, but the variability within the reticulocyte population was greater. The possible influence of this increased rigidity on cell egress from the bone marrow was tested using an in vitro model of the thin endothelial pores found within the marrow. A silicon wafer approximately 0.1 microns in thickness and containing a small (1.2-microns diameter) pore in its center was cemented over the tip of a large (15.0-microns ID) micropipette. The passage of cells through the pore was observed as a function of the pressure across the pore. Consistent with the difference in mechanical properties, the reticulocytes required greater pressures (as great as 4.0 mm Hg compared with less than 1.0 mm Hg) and took longer to traverse the pore. These measurements support the postulate that deformability is important in the regulation of the release of cells from bone marrow.

Purkinje cell degeneration associated with erythroid ankyrin deficiency in nb/nb mice

Mice homozygous for the nb mutation (Chromosome 8) have a severe hemolytic anemia and develop a psychomotor disorder at 6 mo of age. The nb/nb mice are deficient in erythroid ankyrin (Ank-1) but, until the present study, the role of Ank-1 and of Ank-2 (brain ankyrin) in disease genesis was unknown. In normal erythroid tissues, we show that two major transcripts are expressed from Ank-1, and one of these is also present at high levels in the cerebellum. By in situ hybridization and immunocytochemistry, Ank-1 localizes to the cerebellar Purkinje cells and, to a lesser extent, the granule cells. In nb/nb mice, Ank-1 transcripts are markedly reduced in both erythroid and neural tissue, and nb/nb Purkinje cells and granule cells are nearly devoid of Ank-1. The neurological syndrome appears concurrently with a dramatic loss of Purkinje cells. Ank-2 maps to Chromosome 3 and its expression is unaffected by the nb mutation. We conclude that Ank-1 is specifically required for Purkinje cell stability and, in its absence, Purkinje cell loss and neurological symptoms appear.

Estrogen modulates phospholipid acylation in red blood cells: relationship to cell aging

Ethinyl estradiol administered in vivo to female rats resulted in a mild anemia with a 120% increase in reticulocytosis. Consistent with a previous study, the red blood cell cholesterol-to-phospholipid molar ratio was decreased by 25%, whereas fatty acyl incorporation was significantly increased into phosphatidylethanolamine (PE) and not into phosphatidylcholine (PC), the major acyl acceptor in red blood cells. Analysis of this estrogen-dependent acylation increase as a function of cell age indicated that it was not expressed in reticulocytes but in erythrocytes and was associated with cell aging. Estrogen was further shown to increase the red blood cell susceptibility to peroxidation generated by incubation with H2O2. Altogether, the results suggest that estrogen indirectly increases phospholipid acylation in red blood cells by decreasing protection against oxidative damage, thereby favoring the action of endogenous phospholipases against oxidized substrates. This occurs predominantly in PE of oldest cells because 1) PE, being more unsaturated than PC, is more sensitive to oxidation, and 2) susceptibility to oxidation increases with cell age.

Rapid increase in red blood cell density driven by K:Cl cotransport in a subset of sickle cell anemia reticulocytes and discocytes

We have previously demonstrated that young normal (AA) and sickle cell anemia (SS) red blood cells are capable of a volume regulatory decrease response (VRD) driven by a K:Cl cotransporter that is activated by low pH or hypotonic conditions. We now report on the characteristics of young SS cells (SS2, discocytes) capable of rapid increase in density in response to swelling. We have isolated cells with high VRD response (H-VRD) and low VRD response (L-VRD) cells by incubation and density-gradient centrifugation under hypotonic conditions. Comparison of these cells in patients homozygous for hemoglobin (Hb)S indicated that H-VRD cells have 91% more reticulocytes (P less than 9 x 10(-9) than L-VRD cells, 25% less HbF (P less than 5.5 x 10(-5), 106% more NEM (N-methylmaleimide)-stimulated K:Cl cotransport activity (P less than 2 x 10(-4), and 86% more volume-stimulated K:Cl cotransport activity (P less than 1.8 x 10(-3). H-VRD and L-VRD cells have similar G-6-PD and Na+/H+ antiport activity. In agreement with the reduced percent HbF in H-VRD cells, F cells (red blood cells that contain fetal Hb) are depleted from the H-VRD population; however, F reticulocytes are enriched in the H-VRD population to the same extent as non-F reticulocytes, which suggests that both F and non-F reticulocytes have a similar initial distribution of volume-sensitive K:Cl cotransport activity but that it may be more rapidly inactivated in F than in S reticulocytes. We find that H-VRD cells consist of 20% reticulocytes (or 79% of all reticulocytes in SS2) and 80% more mature cells. This study demonstrates the role of K:Cl cotransport in determining red blood cell density, the heterogeneity of K:Cl cotransport activity in reticulocytes, and the capacity for rapid change in the density of reticulocytes with high K:Cl cotransport activity. We speculate that the H-VRD population may be more susceptible to generation of dense and irreversibly sickled cells.

Human alpha-globin genes demonstrate autonomous developmental regulation in transgenic mice

Recent studies have demonstrated that transcriptional activation of the human adult beta-globin transgene in mice by coinsertion of the beta-globin cluster locus control region (beta-LCR) results in loss of its adult restricted pattern of expression. Normal developmental control is reestablished by coinsertion of the fetal gamma-globin transgene in cis to the adult beta-globin gene. To test the generality of this interdependence of two globin genes for their proper developmental control, we generated transgenic mice in which the human adult alpha-globin genes are transcriptionally activated by the beta-LCR either alone or in cis to their corresponding embryonic zeta-globin gene. In both cases, the human globin transgenes were expressed at the appropriate developmental period. In contrast to the beta-globin gene, developmental control of the human adult alpha-globin transgenes appears to be autonomous and maintained even when activated by an adjacent locus control region.

Severe reductions in transcripts for cytochrome c oxidase during erythropoiesis in vitro do not lead to inactive mitochondria in reticulocytes

At some stage during erythroid cell differentiation proliferation of the cell stops and its organelles are removed and degraded. We wanted to know how mitochondrial function correlated with the synthesis of products necessary for functional mitochondria. We studied the time course of the presence of a nuclear and a mitochondrial transcript for the mitochondrial enzyme cytochrome c oxidase as well as that of the enzyme activity itself in differentiating murine splenic erythroid progenitors (erythroid colony-forming units, CFU-E) in vitro. Whereas the amount of total RNA as well as the transcripts for subunits II and IV of cytochrome c oxidase (COX II and COX IV) per cell decreased to low levels, the amount of globin mRNA increased from zero in CFU-E (t = 0) to high levels in late erythroblasts (21 h). Thus, RNA synthesis as such was not inhibited. The cytochrome c oxidase activity also declined. In the total culture, total RNA as well as the mRNAs for COX II and IV decreased after 7 h. The enzyme activity increased until 21 h and decreased after that. The early decrease of the transcripts, followed after a lag phase of 14 h by a decrease in enzyme activity, ultimately does not result in inactive mitochondria in the reticulocyte stage, as was shown with a mitochondria-specific fluorescent probe.

Analysis by cell hybridization of mechanisms that regulate beta-adrenergic responses in reticulocytes and in differentiating erythroid cells

In intact reticulocytes, but not in fragmented membranes, the loss of adenylate cyclase activity during cell maturation followed a biphasic time course. A rapid phase (t1/2 approximately 2 h) during which the initial activity was reduced by 40-50% was followed by a slow phase with t1/2 close to 3 days. The fast decay seemed to occur on the adenylate cyclase level since (-)isoprenaline- or forskolin-stimulated activities behaved similarly and bacterial toxin-monitored Gs and Gi proteins remained stable. The mechanism of the initial decrease in hormonal responsiveness was further analysed in hybrid cells prepared by fusing reticulocytes with Friend erythroleukemia (MEL) cells. The hybrids contained reticulocyte-derived beta-adrenoceptors and MEL cell-derived adenylate cyclase and G proteins. Fusion of reticulocytes to native MEL cells caused adenylate cyclase activity to drop by 30% at 2 h and 45% at 18 h after fusion. By contrast, hybrids prepared after dimethylsulfoxide-induced differentiation of MEL cells showed stable or increasing rates of receptor-coupled cAMP formation between 2 and 18 h after fusion, concomitant with the enhanced activity of the Gs protein in these cells. A cyclase-stimulating factor present in the cytosol of MEL cells and of reticulocytes appeared not to be involved in short-term regulation of hormonal responsiveness. We conclude that the strength of beta-adrenergic responses in erythroid progenitor cells is primarily regulated by modulating G protein-mediated receptor cyclase coupling while reticulocytes, during early maturation, seem to rely on direct inactivation of adenylate cyclase, probably via a cytosolic proteolytic pathway.

CD4+ and CD8+ T lymphocytes both contribute to acquired immunity to blood-stage Plasmodium chabaudi AS

In the present study, the contribution of CD4+ and CD8+ T lymphocytes to acquired immunity to blood-stage infection with the murine malaria species Plasmodium chabaudi AS was investigated. C57BL/6 mice, which are genetically resistant to infection with this hemoprotozoan parasite and exhibit a transient course of infection, were treated intraperitoneally with monoclonal antibodies to T-cell epitopes, either anti-Thy-1, anti-CD4, or anti-CD8. After intraperitoneal infection with 10(6) parasitized erythrocytes, control C57BL/6 mice exhibited a peak parasitemia on day 9 of approximately 35% parasitized erythrocytes and eliminated the infection within 4 weeks. Mice depleted of Thy-1+ or CD4+ T cells had significantly higher parasitemias on day 7 as well as significantly higher peak parasitemias. These mice were unable to control the infection and developed a persistent, high parasitemia that fluctuated between 40 and 60% until the experiment was terminated on day 56 postinfection. Depletion of CD8+ T lymphocytes was found to have no effect on the early course of parasitemia or on the level of peak parasitemia. However, mice depleted of CD8+ T cells experienced two recurrent bouts of parasitemia during the later stage of the infection and required more than 5 weeks to eliminate the parasites. After the peak parasitemia, which occurred in control and experimental animals on day 9, there was a sharp drop in parasitemia coinciding with a wave of reticulocytosis. Therefore, the contribution of the influx of reticulocytes, which are not the preferred host cell of this hemoprotozoan parasite, to limiting the parasitemia was also examined by determining the course of reticulocytosis during infection in control and T cell-depleted animals. Early in infection, there was a marked and comparable reticulocytosis in the peripheral blood of control and T cell-depleted mice; the reticulocytosis peaked on day 12 and coincided with the dramatic and sudden reduction in parasitemia occurring in all groups. In both control and CD8-depleted mice the percentage of reticulocytes decreased as the infection was resolved, whereas in CD4-depleted mice marked reticulocytosis correlated with high, persistent parasitemia. These results thus demonstrate that both CD4+ and CD8+ T cells are involved in acquired immunity to blood-stage P. chabaudi AS and that the influx of reticulocytes into the blood that occurs just after the peak parasitemia may contribute temporarily to limiting the parasitemia.

Erythrocyte maturation in neonatal dwarf and landrace kids

The morphology of the erythrocyte cell series was investigated in external jugular vein blood samples from Dwarf and Danish Landrace goats aged from one day to 12 months. Three erythrocytic cell types were observed in neonates after supravital staining with new methylene blue. The first type were macrocytes which were stained uniformly dark to muddy blue. They formed the majority of the erythrocytic cells at birth and were categorized as diffusely basophilic chromatophilic erythrocytes. The second type were punctate and aggregated reticulocytes, and the third type were mature erythrocytes. The size ranges of the three erythrocytic cells were 4.2-5.6, 4.9-6.3 and 2.8-3.5 microns diameter respectively in the Dwarf kids and 5.6-9.7, 4.2-9.0 and 3.8-4.2 microns respectively in the Landrace kids during the first week of life. Romanowsky-stained blood smears from neonatal kids were characterized by anisocytosis and poikilocytosis in which polychromatophilic macrocytes were numerous, but reticulocytes were not clearly identifiable. The ranges of erythrocyte diameters in Romanowsky-stained neonatal blood films were 4.4-5.8 (5.2 +/- 0.39) and 4.1-6.7 (5.1 +/- 0.67) microns in Dwarf and Landrace kids respectively, decreasing to 3.0 +/- 0.15 and 3.3 +/- 0.13 microns in the two broods respectively by 12 months of age. The numbers of diffusely basophilic polychromatophilic erythrocytes and punctate/aggregated reticulocytes diminished with age and they were not observed in 1-2-month-old kids.

Prednisolone and danazol for treatment of immune-mediated anemia, thrombocytopenia, and ineffective erythroid regeneration in a dog

Immune-mediated anemia and thrombocytopenia were diagnosed in an 8-year-old spayed Miniature Schnauzer. The initial CBC indicated poor erythroid regeneration and concurrent leukopenia. The results of a Coombs test and ANA titer were strongly positive. Examination of a bone marrow specimen revealed erythrophagocytosis and a maturation arrest in the RBC series. Treatment with transfusion plus prednisolone and an attenuated androgen (danazol) resulted in stabilization of the PCV and the development of reticulocytosis.

The spleen in malaria: the role of barrier cells

I believe that my laboratory has developed a construct of the spleen useful in understanding its range of normal and pathologic functions. The elements in the construct include recognition of an anatomically open vasculature with the interposition of reticular cell-reticular fiber filtration beds between terminal arterial vessels and proximal venules. The central function of the spleen, moreover--selective clearance of cells, microbes and other particles from the blood--depends upon these filtration beds. Such functions of the spleen as phagocytosis, immunologic reactivity, hematopoiesis, and blood cell storage derive from its clearance capacities. The reticular filtration beds offer but modest levels of basal clearance. The wide ranges of filtration that characterize the stressed spleen depend upon arming or augmenting the basic reticular filtration beds with responsive cells which can rapidly appear, and rapidly disappear. These include macrophages, salient phagocytic cells of rich repertoire, which have been accorded the major, even exclusive, role in splenic clearance. But other stromal cells participate in splenic clearance. I have identified a system of fibroblastic, contractile, granulated cells which fuse to form complex, branched syncytial sheets which, deployed as diverse barriers, augment the basic reticular filtration beds. Hence, I term these cells barrier cells. Barrier cells effectively interact with macrophages, reticular cells, other stromal and blood cells, contributing to the extraordinary range of splenic clearance capacities. Barrier cells may be elicited by a variety of infectious processes, damaged blood cells and hematopoietic factors. Interleukin-1-alpha evokes a strong barrier cell response, and may be the common denominator in splenic stress, stimulated by activated macrophages.(ABSTRACT TRUNCATED AT 250 WORDS)

Molecular analysis of insertion/deletion mutations in protein 4.1 in elliptocytosis. II. Determination of molecular genetic origins of rearrangements

Protein 4.1 is an approximately 80-kD structural protein in the membrane skeleton which underlies and supports the erythrocyte plasma membrane. The preceding companion paper presents a biochemical study of two abnormal protein 4.1 species from individuals with the red blood cell disorder, hereditary elliptocytosis. These variants, "protein 4.1(68/65)" and "protein 4.1(95)," have altered molecular weights due to internal deletions and duplications apparently localized around the spectrin-actin binding domain. Here we use polymerase chain reaction (PCR) techniques to clone and sequence the corresponding mutant reticulocyte mRNAs, and correlate the deletion/duplication end points with exon boundaries of the gene. Protein 4.1(68/65) mRNA lacks sequences encoding the functionally important spectrin-actin binding domain due to a 240 nucleotide (nt) deletion spanning the codons for Lys407-Gly486. Protein 4.1(95) mRNA encodes a protein with two spectrin-actin binding domains by virtue of a 369 nt duplication of codons for Lys407-Gln529. These deletions and duplications correspond to gene rearrangements involving three exons encoding 21, 59, and 43 amino acids, respectively. The duplicated 21 amino acid exon in the 4.1(95) gene retains its proper tissue-specific expression pattern, being spliced into reticulocyte 4.1 mRNA and out of lymphocyte 4.1 mRNA.

[Perioperative anemia and erythropoiesis]

50 consecutive patients with hip arthroplasty had acute normovolaemic haemodilution and intra- and postoperative autotransfusion using Autotrans, Dideco GmbH. 18 of 50 patients received homologous blood products additionally to autotransfusion (Hb less than 8 g/dl, hemodynamic instability). There was no evidence for coagulation disorders, hypoxia or hypovolaemia during the whole investigation period (until the 10th p.o. day) though in some cases haemoglobin-levels less than 7 g% were accepted. No variations of erythropoietin levels could be observed postoperatively, suggesting that acute anaemia alone does not affect erythropoiesis. Reticulocytes, however, increased significantly from the 4th postoperative day. There was no correlation between number of reticulocytes and erythropoietin levels. Lactate levels stayed within normal range during the whole investigation period thus indicating normal microcirculation. The present data demonstrate that postoperative anaemia can be tolerated even in elder patients if intravascular volume is kept constant (normovolaemia). In accordance with recent literature the course of erythropoietin levels seemed to prove that there was no functional reduction in oxygen-availability.

Analysis of the tetrahydrobiopterin synthesizing system during maturation of murine reticulocytes

The enzymes of tetrahydrobiopterin synthesis have been studied in murine bone marrow, in spleen, in erythrocytes, and in reticulocytes. Mice with chemically induced and with genetically conditioned reticulocytosis as found in the lactate dehydrogenase deficient strain (Ldh-1c/Ldh-1c) were used for analysis of reticulocytic enzyme activities. The activity of the biopterin synthesizing system is highest in bone marrow even though it amounts to only about 10% as compared with liver. The first enzyme of the biosynthetic pathway, GTP-cyclohydrolase, virtually disappears during the final maturation step of reticulocytes. In contrast, the activities of 6-pyruvoyltetrahydropterin synthase and of sepiapterin reductase of erythrocytes are only reduced to about one half of the reticulocyte level. The absence of biopterin in erythrocytes is therefore caused by the loss of the enzyme that initiates the pterin biosynthetic pathway.

Dynamic change of the vascular wall from transmural to intercellular passage of red blood cells observed in splenic regeneration

Rat splenic tissues were autotransplanted into the major omentum, and the operated animals were treated with phenylhydrazine to investigate the passage of erythrocytes through the vascular wall during splenic regeneration. Both ways of the passage were differentiated during regeneration. From day 1 to day 5 after transplantation, the pores were formed in the endothelial cells, through which erythrocytes (chiefly reticulocytes) migrated, and were closed by the basal lamina when erythrocytes did not penetrate. From day 7 to day 10, endothelial cells proliferated, and some of them were transformed into sinus endothelial cells containing condensed microfilaments and formed the interendothelial slit, but few erythrocytes passed there at this stage yet. On and after day 11, when the sinus endothelial cells exhibited well-developed microfilaments, reticular cells contained moderately developed microfilaments and the basal lamina developed well, the slits were opened, where a large number of erythrocytes passed. These results showed, concerning the passage of blood cells, that the vascular wall in the splenic autografts changed from the transmural pattern to the intercellular one after a marked proliferation of endothelial cells and that the effective passage of erythrocytes was closely associated with the development of microfilaments in the cytoplasm of endothelial cells and basal lamina as well as the interaction of reticular cells.

Reticulocyte maturation and exosome release: transferrin receptor containing exosomes shows multiple plasma membrane functions

Vesicles (exosomes) released during sheep reticulocyte maturation contain a number of plasma membrane functions. Using an antibody coated, magnetic core bead, it has been shown unequivocally that vesicles that contain the transferrin receptor also contain other plasma membrane activities, such as the nucleoside transporter and acetylcholinesterase. Lysosomal activities, normally found in the same pellet, are excluded from the transferrin receptor-containing exosomes, suggesting that there is a common mechanism to segregate and externalize specific plasma membrane proteins. In addition to the sheep, electron micrographic studies show that exosomes can be retrieved from the circulation of anemic pigs, rats, and rabbits.

NMR studies of intracellular free calcium, free magnesium and sodium in the guinea pig reticulocyte and mature red cell

During the maturation process reticulocytes lose their intracellular organelles and undergo changes in membrane lipid composition and ion transport properties. While several reports indicate differences in the levels of magnesium, sodium and calcium in reticulocytes and erythrocytes, controversy remains concerning the actual magnitude and direction of ionic alterations during reticulocyte maturation. One problem with all of these studies is that the techniques used are invasive and are limited to measuring only the total cell ion content. We have used 31P, 23Na and 19F nuclear magnetic resonance (NMR) spectroscopy to compare the intracellular free ion and phosphometabolite levels in guinea pig reticulocytes and mature red blood cells. In contrast to a sharply decreased concentration of ATP in erythrocytes in comparison to reticulocytes, the intracellular free magnesium, measured using 31P-NMR, was increased by about 65% upon maturation (150 mumol/l cell water in reticulocytes in comparison to 250 mumol/l cell water in erythrocytes). Sizeable but opposite changes in intracellular sodium (5.5 mumol/ml cells in reticulocytes vs. 8.5 mumol/ml cells in erythrocytes) and intracellular free calcium (99 nM vs. 31 nM in reticulocytes and mature red cells, respectively) were also observed, suggesting that alterations in the kinetics of membrane ion transport systems, accompanying changes in phospholipid and cholesterol content, occur during the process of red cell maturation. However, in contrast to dog red blood cells, there was no evidence for the presence of a Na+/Ca2+ exchanger in guinea pig reticulocytes or erythrocytes.

Membrane assembly and remodeling during reticulocyte maturation

Membrane skeletal and cytoskeletal remodeling occurs throughout erythroid maturation. Microtubules and microfilaments have been identified morphologically in the nucleated erythroblast but the functional capability of these cytoskeletal structures during reticulocyte maturation has not been studied. Reticulocytes are formed from orthochromatic normoblasts by the process of nuclear extrusion. Two recognizable stages of reticulocyte maturation follow. The least mature reticulocytes are motile and multilobular, while the more mature reticulocytes are cup-shaped and nonmotile. To study the respective roles of microtubules and microfilaments in nuclear extrusion and cell motility, experiments were performed with agents that perturb these structures. Following the injection into rats of colchicine, a microtubule-disrupting substance, the number of normoblasts arrested at the stage of nuclear extrusion increased linearly over four hours. Similar results were obtained when bone marrow cells were incubated in culture in the presence of colchicine. In contrast, cell motility was dramatically decreased by cytochalasin B, a microfilament-disrupting agent, but not by colchicine. These results imply that microtubules are essential for the nuclear extrusion process, while microfilaments are essential for cell motility. Simultaneous changes in membrane skeletal assembly were assessed by measuring membrane deformability and stability, two properties regulated by the skeletal proteins. In ektacytometric assays, membrane deformability and mechanical stability of immature reticulocytes were markedly decreased to approximately 10% of normal, while that of more mature reticulocytes were nearly normal. Since the skeletal protein organization regulates these membrane properties, our findings imply that substantial membrane skeletal remodeling occurs during reticulocyte maturation. Thus we have identified major remodeling of both skeletal and cytoskeletal components during reticulocyte maturation.

Flow cytometric reticulocyte quantification using thiazole orange provides clinically useful reticulocyte maturity index

Flow cytometric reticulocyte quantification with thiazole orange has been reported to be of potential utility in a clinical hematology laboratory. We have instituted this technique into routine clinical testing for 18 months and we describe this experience. Flow cytometric analysis provided not only reproducible, cost-effective reticulocyte quantification, but a quantitative reticulocyte maturity index proportional to the amount of RNA in the reticulocytes. The reticulocyte maturity index measurement represents an independent parameter of erythropoiesis, which provided clinically valuable information regarding bone marrow engraftment in patients following autologous bone marrow transplantation. The findings of this study demonstrate the clinical utility of thiazole orange reticulocyte analysis and indicate the diagnostic importance of the reticulocyte maturity index measurement in the evaluation of erythropoietic activity.

Calcium chelators induce association with the detergent-insoluble cytoskeleton and functional inactivation of the transferrin receptor in reticulocytes

Incubation of reticulocytes with EDTA, EGTA (ethylene glycol bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid) and BAPTA (1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid), but not with desferrioxamine B, at temperatures above 20 degrees C resulted in the loss of their ability to take up iron in a temperature-, time- and concentration-dependent manner. No inhibition of transferrin or iron uptake occurred if the incubations were performed at 20 degrees C or below. At higher temperatures, the inhibition was attributable to loss of functional transferrin receptors, not to altered affinity or endocytosis of the remaining receptors. The changes could not be reversed by washing the cells and reincubation in the presence of Ca2+, Mg2+ or Zn2+. However, they could be completely prevented by performing the initial incubation with chelators in the presence of diferric transferrin and partly prevented by the use of apotransferrin. Incubation with the chelators resulted in much less reduction in the ability of the cells to bind anti-transferrin receptor immunoglobulin than transferrin. The fate of the receptor was studied by polyacrylamide gel electrophoresis of reticulocyte membrane proteins before and after extraction with Triton X-100, and by immunological staining of Western blots for the transferrin receptor. Treatment of the cells with EDTA led to a loss of the ability of Triton X-100 to solubilize the receptor and its retention in the Triton-insoluble cytoskeletal matrix of the cells. It is concluded that incubation of reticulocytes with the chelators at temperatures above 20 degrees C causes an altered interaction of the transferrin receptor with the cytoskeleton. This change, which is probably due to chelation of Ca2+ in the cell membrane, is accompanied by an irreversible loss of the receptor's ability to bind transferrin.

Microvascular sites and characteristics of sickle cell adhesion to vascular endothelium in shear flow conditions: pathophysiological implications

To understand the role of sickle cell adherence to the vascular endothelium in the pathophysiology of sickle cell anemia (SS) vasoocclusion, we have carried out a microcirculatory study utilizing the ex vivo mesocecum vasculature of the rat. A single bolus of washed oxy-normal (AA) erythrocytes or oxy-SS cells (unseparated or density-defined SS cell classes) was infused. Hemodynamic monitoring and intravital microscopic observations of the microvascular flow revealed higher peripheral resistance for SS erythrocytes and adherence of these cells exclusively to the venular endothelium but rare or no adherence of AA cells. The extent of adhesion was inversely correlated with venular diameters (r = -0.812; P less than 0.00001). The adhesion of SS erythrocytes is density-class dependent: reticulocytes and young discocytes (SS1) greater than discocytes (SS2) greater than irreversible sickle cells and unsicklable dense discocytes (SS4). Selective secondary trapping of SS4 (dense cells) is found in postcapillary venules where deformable SS cells are preferentially adhered. We conclude that in the oxygenated condition, vasoocclusion can be induced by two events: (i) random precapillary obstruction by a small number of SS4 cells; (ii) increased adhesion of SS1 and SS2 cells in the immediate postcapillary venules. A combination of precapillary obstruction, adhesion in postcapillary venules, and secondary trapping of dense cells may induce local hypoxia, increased polymerization of hemoglobin S, and rigidity of SS erythrocytes, thereby extending obstruction to nearby vessels.

Cell membrane and volume changes during red cell development and aging

This paper provides a summary of our understanding of cell membrane and volume changes during red cell development and aging. Cytoskeletal structures which include microtubules and microfilaments appear to play key roles in the genesis of the anucleate reticulocyte from its nucleated precursor cell, as well as in the early stages of reticulocyte development. The maturation of reticulocyte into red cell is accompanied by marked changes in cell shape and extensive remodeling of the membrane skeleton, resulting in the mature red cell acquiring a highly deformable yet remarkably stable membrane. The volume and cell density heterogeneity seen for circulating red cells also appears to be the result of the membrane changes that occur during reticulocyte maturation. Following its genesis from reticulocyte, the mature red cell undergoes further membrane and volume changes during its life span of 120 days. While it is clear that surface area loss, decrease in cell volume and cell surface modifications leading to binding of immunoglobulins accompany red cell aging, the cardinal cellular modification responsible for the removal of senescent red cells from the circulation is yet to be defined.