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Concept: Reticulocyte

166

The quantity of circulating reticulocytes is an important indicator of erythropoietic activity in response to a wide range of haematological pathologies. While most modern laboratories use flow cytometry to quantify reticulocytes, most field laboratories still rely on ‘subvital’ staining. The specialist ‘subvital’ stains, New Methylene Blue (NMB) and Brilliant Crésyl Blue are often difficult to procure, toxic, and show inconsistencies between batches. Here we demonstrate the utility of Giemsa’s stain (commonly used microbiology and parasitology) in a ‘subvital’ manner to provide an accurate method to visualize and count reticulocytes in blood samples from normal and malaria-infected individuals.

Concepts: Biology, Red blood cell, Anemia, Hematology, Flow cytometry, Stain, Reticulocyte, New methylene blue

30

Understanding how malaria parasites gain entry into human red blood cells is essential for developing strategies to stop blood stage infection. Plasmodium vivax preferentially invades reticulocytes, which are immature red blood cells. The organism has two erythrocyte-binding protein families: namely, the Duffy-binding protein (PvDBP) and the reticulocyte-binding protein (PvRBP) families. Several members of the PvRBP family bind reticulocytes, specifically suggesting a role in mediating host cell selectivity of P. vivax. Here, we present, to our knowledge, the first high-resolution crystal structure of an erythrocyte-binding domain from PvRBP2a, solved at 2.12 Å resolution. The monomeric molecule consists of 10 α-helices and one short β-hairpin, and, although the structural fold is similar to that of PfRh5-the essential invasion ligand in Plasmodium falciparum-its surface properties are distinct and provide a possible mechanism for recognition of alternate receptors. Sequence alignments of the crystallized fragment of PvRBP2a with other PvRBPs highlight the conserved placement of disulfide bonds. PvRBP2a binds mature red blood cells through recognition of an erythrocyte receptor that is neuraminidase- and chymotrypsin-resistant but trypsin-sensitive. By examining the patterns of sequence diversity within field isolates, we have identified and mapped polymorphic residues to the PvRBP2a structure. Using mutagenesis, we have also defined the critical residues required for erythrocyte binding. Characterization of the structural features that govern functional erythrocyte binding for the PvRBP family provides a framework for generating new tools that block P. vivax blood stage infection.

Concepts: Hemoglobin, Protein, Cell nucleus, Blood, Malaria, Red blood cell, Receptor, Reticulocyte

28

Nucleated red blood cells (NRBCs) and reticulocytes are early and important measures of red blood cells' (RBCs) turnover, but little is known on how spurious hemolysis may affect the reliability of these parameters.

Concepts: Hemoglobin, Cell nucleus, Blood, Red blood cell, Anemia, Hematology, Blood cells, Reticulocyte

28

Reticulocytes are the most sensitive index available to authorities who seek to sanction athletes for blood doping based on deviations beyond individual reference ranges. Because such data comprise longitudinal results that are generated by different laboratories, the comparability of reticulocyte counts from different instruments is of crucial importance.

Concepts: Red blood cell, Anemia, Reticulocyte, Musical instrument, Tour de France

3

This study was a prospective cross-sectional cohort study of 125 patients with sickle cell anemia (SS) between the ages of 16 to 60 years. Enrolled patients were followed-up prospectively for 15 months. Demographic, clinical, hematological and routine biochemical data were obtained on all patients. Six-minute walk test and Doppler Echocardiography were performed on all patients. A tricuspid regurgitant jet velocity (TRJV) < 2.5 m/sec was considered normal, 2.5 ≤ TRJV ≤ 3.0 was considered mild-moderate and > 3.0 m/sec, severe. Patients with abnormal TRJV were significantly older and more anemic, had significantly higher lactate dehydrogenase (LDH) levels, reticulocyte count and incidence of death. The logistic multimodal model implemented for the 125 patients indicated that age was the covariate that influenced the outcome of normal or abnormal TRJV with a cutoff age of thirty-two years. The survival rate for the group of patients with creatinine (Cr) > 1.0 mg/dL was lower than the group with Cr ≤ 1 and normal TRJV. A coefficient matrix showed that the LDH values were weakly correlated with the reticulocyte count but strongly correlated with hemoglobin suggesting that the TRJV values were not correlated with the hemolytic rate but with anemia. Ten patients died during the follow-up of whom 7 had TRJV > 2.5 m/sec. Acute chest syndrome was the most common cause of death followed by sepsis. In conclusion, this study shows that patients with SS older than thirty-two years with high LDH, elevated TRJV, severe anemia and Cr > 1 have poor prognosis and may be at risk of having pulmonary hypertension and should undergo RHC.

Concepts: Hemoglobin, Red blood cell, Demography, Doppler echocardiography, Anemia, Lactate dehydrogenase, Sickle-cell disease, Reticulocyte

2

Erythropoiesis is marked by progressive changes in morphological, biochemical and mechanical properties of erythroid precursors to generate red blood cells (RBC). The earliest enucleated forms derived in this process, known as reticulocytes, are multi-lobular and spherical. As reticulocytes mature, they undergo a series of dynamic cytoskeletal re-arrangements and the expulsion of residual organelles, resulting in highly deformable biconcave RBCs (normocytes). To understand the significant, yet neglected proteome-wide changes associated with reticulocyte maturation, we undertook a quantitative proteomics approach. Immature reticulocytes (marked by the presence of surface transferrin receptor, CD71) and mature RBCs (devoid of CD71) were isolated from human cord blood using a magnetic separation procedure. After sub-fractionation into triton-extracted membrane proteins and luminal samples (isobaric tags for relative and absolute quantitation), quantitative mass spectrometry was conducted to identify more than 1800 proteins with good confidence and coverage. While most structural proteins (such as Spectrins, Ankyrin and Band 3) as well as surface glycoproteins were conserved, proteins associated with microtubule structures, such as Talin-½ and ß-Tubulin, were detected only in immature reticulocytes. Atomic force microscopy (AFM)-based imaging revealed an extended network of spectrin filaments in reticulocytes (with an average length of 48 nm), which shortened during reticulocyte maturation (average spectrin length of 41 nm in normocytes). The extended nature of cytoskeletal network may partly account for increased deformability and shape changes, as reticulocytes transform to normocytes.

Concepts: Protein, Cell nucleus, Blood, Cell membrane, Red blood cell, Anemia, Blood cells, Reticulocyte

1

The invasion of CD71+ reticulocytes by Plasmodium vivax is a crucial yet poorly characterized event. The application of flow cytometry to ex vivo invasion assays promises to facilitate the quantitative analysis of P. vivax reticulocyte invasion. However, current protocols suffer from a low level of sensitivity due to the absence of a particular design for P. vivax cell tropism. Importantly, merozoite invasion into contaminating red blood cells (RBCs) from the schizont inoculum (auto-invasion) may confound the analysis. Here we present a stable two-color flow cytometry assay for the accurate quantification of P. vivax merozoite invasion into intracellularly labelled CD71+ reticulocytes. Various enzymatic treatments, antibodies and invasion inhibitory molecules were used to successfully demonstrate the utility of this method. Fluorescent labelling of RBCs did not affect the invasion and early intra-erythrocytic development of P. vivax. Importantly, this portable field assay allows for the economic usage of limited biological material (parasites and reticulocytes) and the intracellular labeling of the target cells reduces the need for highly purified schizont inoculums. This assay will facilitate the study of P. vivax merozoite biology and the testing of vaccine candidates against vivax malaria.

Concepts: Cell nucleus, Blood, Malaria, Cell membrane, Red blood cell, Apicomplexa, Anemia, Reticulocyte

1

Anaemia following hip fracture is common. Approximately 30 to 45% of patients have haemoglobin concentrations below population norms on admission, and around 10% are severely anaemic. Anaemia on admission, and in the postoperative period, is associated with poor outcomes with regard to mobility, postoperative mortality and readmission. There is currently no clear consensus on the optimal method of managing perioperative anaemia in this group of frail patients with frequent comorbidity. Liberal red cell transfusion in the postoperative period does not appear to improve outcome, whereas tranexamic acid appears to reduce transfusion rate at the expense of increased cardiovascular morbidity. There are encouraging results from one centre with the use of agents to stimulate red cell production, including intravenous iron and erythropoietin. UK practice differs significantly from these patients and these studies, and it is not clear whether these promising results will translate to the UK population.Methods/design: This is a single-centre randomized controlled parallel group trial, in a British university hospital.andomization is achieved using a website and computer-generated concealed tables. Participants are 80 patients 70 years or over with acute hip fracture undergoing operative repair. The intervention group receive three daily infusions of 200 mg iron sucrose, starting within 24 hours of admission. The control group receive standard hospital care at the discretion of the clinical team. Red cell transfusions for each group are given in accordance with standard clinical triggers. The primary outcome is an increase in mean reticulocyte count in the intervention group at day 7. Secondary outcome measures include haemoglobin concentrations, early and late transfusion rates, infectious and cardiovascular complications, mobility and 30-day mortality.

Concepts: Hemoglobin, Osteoporosis, Epidemiology, Red blood cell, Randomized controlled trial, Anemia, Clinical research, Reticulocyte

0

No full consensus exists on which iron status parameters to use for iron status assessment. In this study, we assessed the usefulness of measurement of the hemoglobin content of reticulocytes (CHr) in the general population.

Concepts: Hemoglobin, Red blood cell, Assessment, Anemia, Reticulocyte

0

Enucleation is the final step in mammalian erythropoiesis. In this process, the nucleus is extruded by budding off from the erythroblast, forming the reticulocyte. Herein, we describe the flow cytometry-based assays for enucleation assessment. The separation of nucleated erythroblasts, reticulocytes, and extruded nuclei by flow cytometry is based on DNA staining, surface expression of erythrocyte specific markers, or forward scatter (FSC). The enucleation of murine erythroblasts is assessed by the surface expression of murine erythrocyte marker Ter119 and DNA staining. Three discrete populations that represent nucleated erythroblasts, reticulocytes, and extruded nuclei are defined as HoechstmedTER119high, HoechstlowTER119high, and HoechsthighTER119med, respectively. Another nuclei acid staining dye, SYTO16, is used for the assessment of human enucleation in combination with FSC. For human cells, the three populations that represent nucleated erythroblasts, reticulocyte, and extruded nuclei are identified as FSChigh SYTO16+, FSChigh SYTO16-, FSClowSYTO16+, respectively.

Concepts: DNA, Gene, Cell nucleus, Gene expression, Cell, Red blood cell, Flow cytometry, Reticulocyte