Innocent Safeukui

The sensing of poorly deformable red blood cells by the human spleen can be mimicked in vitro

Retention of poorly deformable red blood cells (RBCs) by the human spleen has been recognized as a critical determinant of pathogenesis in hereditary spherocytosis, malaria, and other RBC disorders. Using an ex vivo perfusion system, we had previously shown that retention of Plasmodium falciparum-infected RBCs (Pf-RBCs) occur in the splenic red pulp, upstream from the sinus wall. To experimentally replicate the mechanical sensing of RBCs by the splenic microcirculation, we designed a sorting device where a mixture of 5- to 25-μm-diameter microbeads mimics the geometry of narrow and short interendothelial splenic slits. Heated RBCs, Pf-RBCs, and RBCs from patients with hereditary spherocytosis were retained in the microbead layer, without hemolysis. The retention rates of Pf-RBCs were similar in microbeads and in isolated perfused human spleens. These in vitro results directly confirm the importance of the mechanical sensing of RBCs by the human spleen. In addition, rigid and deformable RBC subpopulations could be separated and characterized at the molecular level, and the device was used to deplete a stored RBC population from its subpopulation of rigid RBCs. This experimental approach may contribute to a better understanding of the role of the spleen in the pathogenesis of inherited and acquired RBC disorders.

Quantitative assessment of sensing and sequestration of spherocytic erythrocytes by the human spleen.

Splenic sequestration of RBCs with reduced surface area and cellular deformability has long been recognized as contributing to pathogenesis of several RBC disorders, including hereditary spherocytosis. However, the quantitative relationship between the extent of surface area loss and splenic entrapment remains to be defined. To address this issue, in the present study, we perfused ex vivo normal human spleens with RBCs displaying various degrees of surface area loss and monitored the kinetics of their splenic retention. Treatment with increasing concentrations of lysophosphatidylcholine resulted in a dose-dependent reduction of RBC surface area at constant volume, increased osmotic fragility, and decreased deformability. The degree of splenic retention of treated RBCs increased with increasing surface area loss. RBCs with a > 18% average surface area loss (> 27% reduced surface area-to-volume ratio) were rapidly and completely entrapped in the spleen. Surface-deficient RBCs appeared to undergo volume loss after repeated passages through the spleen and escape from splenic retention. The results of the present study for the first time define the critical extent of surface area loss leading to splenic entrapment and identify an adaptive volume regulation mechanism that allows spherocytic RBCs to prolong their life span in circulation. These results have significant implications for understanding the clinical heterogeneity of RBC membrane disorders.

Proof of principle for transfusion of in vitro–generated red blood cells

In vitro RBC production from stem cells could represent an alternative to classic transfusion products. Until now the clinical feasibility of this concept has not been demonstrated. We addressed the question of the capacity of cultured RBCs (cRBCs) to survive in humans. By using a culture protocol permitting erythroid differentiation from peripheral CD34(+) HSC, we generated a homogeneous population of cRBC functional in terms of their deformability, enzyme content, capacity of their hemoglobin to fix/release oxygen, and expression of blood group antigens. We then demonstrated in the nonobese diabetes/severe combined immunodeficiency mouse that cRBC encountered in vivo the conditions necessary for their complete maturation. These data provided the rationale for injecting into one human a homogeneous sample of 10(10) cRBCs generated under good manufacturing practice conditions and labeled with (51)Cr. The level of these cells in the circulation 26 days after injection was between 41% and 63%, which compares favorably with the reported half-life of 28 ± 2 days for native RBCs. Their survival in vivo testifies globally to their quality and functionality. These data establish the proof of principle for transfusion of in vitro-generated RBCs and path the way toward new developments in transfusion medicine. This study is registered at http://www.clinicaltrials.gov as NCT0929266.

The pathogenesis of Plasmodium falciparum malaria in humans: insights from splenic physiology

Clinical manifestations of Plasmodium falciparum infection are induced by the asexual stages of the parasite that develop inside red blood cells (RBCs). Because splenic microcirculatory beds filter out altered RBCs, the spleen can innately clear subpopulations of infected or uninfected RBC modified during falciparum malaria. The spleen appears more protective against severe manifestations of malaria in naïve than in immune subjects. The spleen-specific pitting function accounts for a large fraction of parasite clearance in artemisinin-treated patients. RBC loss contributes to malarial anemia, a clinical form associated with subacute progression, frequent splenomegaly, and relatively low parasitemia. Stringent splenic clearance of ring-infected RBCs and uninfected, but parasite-altered, RBCs, may altogether exacerbate anemia and reduce the risks of severe complications associated with high parasite loads, such as cerebral malaria. The age of the patient directly influences the risk of severe manifestations. We hypothesize that coevolution resulting in increased splenic clearance of P. falciparum-altered RBCs in children favors the survival of the host and, ultimately, sustained parasite transmission. This analysis of the RBC-spleen dynamic interactions during P falciparum infection reflects both data and hypotheses, and provides a framework on which a more complete immunologic understanding of malaria pathogenesis may be elaborated.

Evaluation of FRET real-time PCR assay for rapid detection and differentiation of Plasmodium species in returning travellers and migrants

BackgroundA simple real-time PCR assay using one set of primer and probe for rapid, sensitive and quantitative detection of Plasmodium species, with simultaneous differentiation of Plasmodium falciparum from the three other Plasmodium species (Plasmodium vivax, Plasmodium ovale and Plasmodium malariae) in febrile returning travellers and migrants was developed and evaluated.MethodsConsensus primers were used to amplify a species-specific region of the multicopy 18S rRNA gene, and fluorescence resonance energy transfer hybridization probes were used for detection in a LightCycler platform (Roche). The anchor probe sequence was designed to be perfect matches to the 18S rRNA gene of the fourth Plasmodium species, while the acceptor probe sequence was designed for P. falciparum over a region containing one mismatched, which allowed differentiation of the three other Plasmodium species. The performance characteristics of the real-time PCR assay were compared with those of conventional PCR and microscopy-based diagnosis from 119 individuals with a suspected clinical diagnostic of imported malaria.ResultsBlood samples with parasite densities less than 0.01% were all detected, and analytical sensitivity was 0.5 parasite per PCR reaction. The melt curve means Tms (standard deviation) in clinical isolates were 60.5°C (0.6°C) for P. falciparum infection and 64.6°C (1.8°C) for non-P. falciparum species. These Tms values of the P. falciparum or non-P. falciparum species did not vary with the geographic origin of the parasite. The real-time PCR results correlated with conventional PCR using both genus-specific (Kappa coefficient: 0.95, 95% confidence interval: 0.9 – 1) or P. falciparum-specific (0.91, 0.8 – 1) primers, or with the microscopy results (0.70, 0.6 – 0.8). The real-time assay was 100% sensitive and specific for differentiation of P. falciparum to non-P. falciparum species, compared with conventional PCR or microscopy. The real-time PCR assay can also detect individuals with mixed infections (P. falciparum and non-P. falciparum sp.) in the same sample.ConclusionThis real-time PCR assay with melting curve analysis is rapid, and specific for the detection and differentiation of P. falciparum to other Plasmodium species. The suitability for routine use of this assay in clinical diagnostic laboratories is discussed.

Acetazolamide and chronic hypoxia: effects on haemorheology and pulmonary haemodynamics

We tested the effect of acetazolamide on blood mechanical properties and pulmonary vascular resistance (PVR) during chronic hypoxia. Six groups of rats were either treated or not treated with acetazolamide (curative: treated after 10 days of hypoxic exposure; preventive: treated before hypoxic exposure with 40 mg·kg−1·day−1) and either exposed or not exposed to 3 weeks of hypoxia (at altitude >5,500 m). They were then used to assess the role of acetazolamide on pulmonary artery pressure, cardiac output, blood volume, haematological and haemorheological parameters. Chronic hypoxia increased haematocrit, blood viscosity and PVR, and decreased cardiac output. Acetazolamide treatment in hypoxic rats decreased haematocrit (curative by -10% and preventive by -11%), PVR (curative by -36% and preventive by -49%) and right ventricular hypertrophy (preventive -20%), and increased cardiac output (curative by +60% and preventive by +115%). Blood viscosity was significantly decreased after curative acetazolamide treatment (-16%) and was correlated with PVR (r=0.87, p<0.05), suggesting that blood viscosity could influence pulmonary haemodynamics. The fall in pulmonary vascular hindrance (curative by -27% and preventive by -45%) after treatment suggests that acetazolamide could decrease pulmonary vessels remodelling under chronic hypoxia. The effect of acetazolamide is multifactorial by acting on erythropoiesis, pulmonary circulation, haemorheological properties and cardiac output, and could represent a pertinent treatment of chronic mountain sickness.

Microsphiltration: A Microsphere Matrix to Explore Erythrocyte Deformability

The altered deformability of erythrocytes infected with Plasmodium falciparum is central in malaria -pathogenesis, as it influences the hemodynamic properties of the infected cell and its retention in the spleen. Exported parasite proteins, as well as the shape and volume of the parasite itself, influence the deformability of the infected erythrocyte. To explore changes in erythrocyte deformability, we have developed a new method, called microsphiltration, based on filtration of erythrocytes through a mixture of metal microspheres that mimic the geometry of inter-endothelial splenic slits. As P. falciparum develops in its host cell, the retention rates observed in microspheres correlate with the progressive decrease of erythrocyte deformability and with the retention rates in the spleen. The yields of microsphiltration separation allow for molecular analyses of subpopulations with distinct mechanical phenotypes.

A role of IgE and CD23/NO immune pathway in age-related resistance of Lewis rats to Plasmodium berghei Anka?

In contrast to young rats, adult rats given i.p. Plasmodium berghei Anka (PbA) control the parasitaemia and repair their anaemia. Here, we investigated whether IgE and CD23/NO immune pathway could be implicated in this age-related resistance of adult rats to PbA. Eight-week-old rats displayed significantly higher levels of plasma total IgE (p=0.01) and soluble CD23 (p=0.003) during the peak of parasitaemia, compared to 4-week-old rats. IgE Fc-binding antibody or aminoguanidine administration to parasitized 8-week-old rats slightly delayed blood parasite clearance or exacerbated anaemia. These data suggest that IgE and CD23/NO could play an important role in the resistance of adult rats experiencing PbA primary intraerythrocytic development.

A micro-bead device to explore Plasmodium falciparum-infected, spherocytic or aged red blood cells prone to mechanical retention by spleen endothelial slits

Experimental tools to identify human red blood cells (RBC) prone to mechanical retention upstream from the spleen venous sinus inter-endothelial slits are currently suboptimal. We designed a micro-bead device mimicking the geometry of the human narrow and short inter-endothelial slits. Upon filtration through a mixture of 5-25 μm diameter micro-beads, Plasmodium falciparum-hosting RBC (Pf-RBC) were retained in a parasite developmental stage-dependent way, the retention rates of a subset of ring-RBC being similar in micro-beads and in isolated-perfused human spleens. We found that this retention might be linked principally to the reduced surface-area-to-volume ratio of Pf-RBC. Interestingly, other rigid RBC, such as heat-treated RBC, and RBC from hereditary spherocytosis patients were also retained in micro-beads without any hemolysis. Micro-beads allow (i) depletion of heterogeneous RBC population from its rigid-RBC subpopulation ii) characteriziation of distinct molecular signatures of rigid versus deformable RBC subpopulations. This simple method portends wide medical applications, such as improving the quality of stored RBC concentrates prior to transfusion.