Surface Of Human Erythrocytes Research Articles

Development of Icephilic ACTIVE Glycopeptides for Cryopreservation of Human Erythrocytes.

Ice formation and recrystallization exert severe impairments to cellular cryopreservation. In light of cell-damaging washing procedures in the current glycerol approach, many researches have been devoted to the development of biocompatible cryoprotectants for optimal bioprotection of human erythrocytes. Herein, we develop a novel ACTIVE glycopeptide of saccharide-grafted ε-poly(L-lysine), that can be credited with adsorption on membrane surfaces, cryopreservation with trehalose, and icephilicity for validity of human erythrocytes. Then, by Borch reductive amination or amidation, glucose, lactose, maltose, maltotriose, or trehalose was tethered to ε-polylysine. The synthesized ACTIVE glycopeptides with intrinsic icephilicity could localize on the membrane surface of human erythrocytes and improve cryopreservation with trehalose, so that remarkable post-thaw cryosurvival of human erythrocytes was achieved with a slight variation in cell morphology and functions. Human erythrocytes (∼50% hematocrit) in cryostores could maintain high cryosurvival above 74%, even after plunged in liquid nitrogen for 6 months. Analyses of differential scanning calorimetry, Raman spectroscopy, and dynamic ice shaping suggested that this cryopreservation protocol combined with the ACTIVE glycopeptide and trehalose could enhance the hydrogen bond network in nonfrozen solutions, resulting in inhibition of recrystallization and growth of ice. Therefore, the ACTIVE glycopeptide can be applied as a trehalose-associated "chaperone", providing a new way to serve as a candidate in glycerol-free human erythrocyte cryopreservation.

Insight into Francisella tularensis-erythrocyte interactions

Francisella tularensis, the causative agent of tularemia, is a pathogenic gram-negative bacterium that enters human red blood cells (RBCs). Previous investigations suggest that invasion of RBCs helps F. tularensis survive in the gut of arthropods – a transmission vector of this bacterium leading to colonization. Since tularemia is a zoonotic infection, humans are not the primary host of F. tularensis. Therefore, we sought to investigate whether F. tularensis was capable of invading RBCs of other animals. Using the gentamicin protection assay, we discovered that while F. tularensis could enter sheep and chicken erythrocytes, bovine RBCs did not support invasion. Because of previous studies published by our lab, and due to intrinsic differences between human and bovine erythrocyte surface protein Band 3, we hypothesized that RBC membrane protein Band 3 is required for invasion. We used anti-band 3 Fab fragments to physically block the Band 3 RBC surface protein and investigated how that impacted F. tularensis invasion. Here, we provide preliminary evidence suggesting that F. tularensis uses Band 3 to enter human RBCs. This study was funded by the National Institute of Allergy and Infectious Diseases (1R15HL147135) and an Institutional Development Award (IDeA) from the National Institute of General Medical Sciences of the National Institutes of Health (P20GM103434), which funds WV-INBRE program.

Human erythrocyte surface fucose expression increases with age and hyperglycemia

Background: Reactive oxygen species and other free radicals, together with glucose and its metabolites are believed to play important roles in the aging process. The carbohydrate components of glycosylated proteins are important in mediating cell-cell interactions and a role has been suggested for them in the aging process. Erythrocytes are critical cells in the human body, heavily glycosylated and relatively easily available and so are good candidates to yield insights into how patterns of glycosylation change with age and disease. It has been claimed, based on a periodic acid Schiff assay, that human aging is associated with a decline of erythrocyte surface sialic acids. Plant lectins allow for more specific assays for glycans, including determining the linkage of sialic acids and analysis of single cells by flow cytometry. Methods: Plant lectins, including Maackia amurensis lectin II (MAL), binding to α-2,3 linked sialic acids and Sambucus nigra (SNA), α-2,6 sialic acids, were used in flow cytometry and western blot of erythrocyte surface membrane. N-glycomics mass spectrometry determines glycan structures. Donors varying in age and hyperglycemia, as indicated by HbA1c were analysed. Results: Erythrocyte surface sialic acids have no significant associations with donor age. A combination of storage and cellular aging produces a specific loss of α-2,6 sialic acids. By contrast, erythrocyte surface terminal fucoses increase significantly with donor age. In order to determine which aspects of aging are important in determining this change, we investigated whether this novel human aging biomarker is associated with higher plasma glucose values, assessed by glycated hemoglobin (HbA1c) and reactive oxygen species (ROS) generation. Fucose levels were associated with HbA1c levels, but not ROS generation. Conclusion: Our study identifies novel glycan-based biomarkers for human aging and disease. The simplicity of lectin-based assays provide an attractive cellular tool to study aging and disease processes.

Cell Surface Functionalization with Heparin‐Conjugated Lipid to Suppress Blood Activation

AbstractOrgan transplantation leads to damage of the endothelial glycocalyx of the transplanted organ, and the activated endothelial surface induces thromboinflammation. The result is dysfunction of the transplanted organ, known as ischemia reperfusion injury (IRI). Long‐term graft survival strongly depends on the regulation of IRI. Here the aim is to reconstruct the glycocalyx to regulate blood activation during IRI. Heparin‐conjugated lipid (fHep‐lipid) is synthesized with 0.6, 1.8, 2.7, 4.5, or 8.0 fragmented heparins per lipid to compare their anticoagulation activity. First, liposome and cells are modified with each fHep‐lipid and the surface properties are evaluated. Then the hemocompatibility of the modified human mesenchymal stem cells (hMSCs) is examined in a loop model using human blood. The antithrombin‐binding capacity and anti‐factor Xa activity of the fHep‐lipids depend on the number of conjugated heparins, with efficacy increasing with increasing number of heparins. The modified liposomes are highly negatively charged and show strong anti‐factor Xa activity. In addition, the cell surfaces of human erythrocytes and hMSCs can be uniformly modified with fHep‐lipid. The whole blood studies reveal that fHep‐lipid on hMSCs can prevent generation of thrombin–antithrombin complexes, coagulation markers, and platelet aggregation, whereas unmodified hMSCs trigger activation of the platelet and coagulation systems.

Tissue expression of antigens of ABH blood groups in species of New World Monkeys (Aotus infulatus, Callithrix jacchus, Sapajus apella and Saimiri sciureus).

ABH antigens are histo-antigens, but were first described on the surface of human erythrocytes. They are found in those cells only in great apes and humans, while in more primitive animals they are found in tissues and body fluids. ABH antigens are mainly distributed in tissues that are in contact with the external environment and may serve as ligands for pathogens in tissues or block their connection. Description of the distribution of these molecules in non-human primate tissues is restricted to a few tissues and species. This paper describes the expression of human A, B and H type antigens in different organs from four species of New World Primates, obtained from the Centro Nacional de Primatas, as well as comparing that expression with what has been described for humans. In this study, although the tissue description of the antigens is similar to the genetic model for humans, some differences in expression between some organs from those species and those of humans were found. The differences occurred mainly in endodermal organs that have secretory functions and are probably under the control of the human-type FUT-2 enzyme. In the mesodermal-origin organs there was a reduction or absence of A and B antigen marking, particularly in the H precursor substance, indicating that those organs are under the control of the human-type FUT-1 enzyme. These findings have demonstrated that there is similar ABH antigen reactivity in tissue distribution between the species, although there are some species-specific cases.

Anchoring Supramolecular Polymers to Human Red Blood Cells by Combining Dynamic Covalent and Non-Covalent Chemistries.

Understanding cell/material interactions is essential to design functional cell‐responsive materials. While the scientific literature abounds with formulations of biomimetic materials, only a fraction of them focused on mechanisms of the molecular interactions between cells and material. To provide new knowledge on the strategies for materials/cell recognition and binding, supramolecular benzene‐1,3,5‐tricarboxamide copolymers bearing benzoxaborole moieties are anchored on the surface of human erythrocytes via benzoxaborole/sialic‐acid binding. This interaction based on both dynamic covalent and non‐covalent chemistries is visualized in real time by means of total internal reflection fluorescence microscopy. Exploiting this imaging method, we observe that the functional copolymers specifically interact with the cell surface. An optimal fiber affinity towards the cells as a function of benzoxaborole concentration demonstrates the crucial role of multivalency in these cell/material interactions.

Quantitative comparative analysis of human erythrocyte surface proteins between individuals from two genetically distinct populations

Red blood cells (RBCs) play a critical role in oxygen transport, and are the focus of important diseases including malaria and the haemoglobinopathies. Proteins at the RBC surface can determine susceptibility to disease, however previous studies classifying the RBC proteome have not used specific strategies directed at enriching cell surface proteins. Furthermore, there has been no systematic analysis of variation in abundance of RBC surface proteins between genetically disparate human populations. These questions are important to inform not only basic RBC biology but additionally to identify novel candidate receptors for malarial parasites. Here, we use ‘plasma membrane profiling’ and tandem mass tag-based mass spectrometry to enrich and quantify primary RBC cell surface proteins from two sets of nine donors from the UK or Senegal. We define a RBC surface proteome and identify potential Plasmodium receptors based on either diminished protein abundance, or increased variation in RBCs from West African individuals.

Effect of 2Me, DTT, ZAAP and Enzyme on JMH Antigen on the Surface of Human Erythrocytes

To explore the the effects of 2-Me, DTT, papain, pineapple protease and ZZAP on the antigenicity of JMH antigen of human red blood cells (RBC) surface. Firstly, human RBC were treated with 2-Me, DTT, pineapple protease, papain and ZZAP reagents, respectively. The antigenicity of JMH antigen on human RBC surface was detected and analyzed by flow cytometry. Flow cytometric analysis found that compared with level before treatment, the antigenicity of JMH antigen on RBC surface was significantly reduced after 2-Me treatment, the positive rate of JMH antigen: 69.5%±4.5% vs 56.5%±3.4% (t=12.44, P＜0.01); fluorescence intensity: 4906±317 vs 3003±165 (t=11.84, P＜0.01). The antigenicity of JMH antigen on RBC surface significantly increased after DTT treatment, showing the positive rate of JMH antigen: 61.7%±3.8% vs 75.5±4.9% (t=16.57, P＜0.01), fluorescence intensity: 4044±294 vs 4854±319 (t=15.46, P＜0.01). However, both bromelain and papain could significantly reduce the antigenicity of JMH antigen on the RBC surface, Bromelain: the positive rate of JMH antigen: 62.2%±3.8% vs 8.8%±1.2% (t=26.44, P＜0.01), fluorescence intensity: 4263±273 vs 1444±212 (t=19.27, P＜0.01); Papain: the positive rate of JMH antigen: 62.8%±3.6% vs 8.8%±1.5% (t=21.38, P＜0.01), fluorescence intensity: 4389±284 vs 1458±230 (t=17.49, P＜0.01). The flow cytometric analysis revealed that ZZAP treatment significantly reduced the antigenicity of JMH antigen on the RBC surface, the positive rate of JMH antigen: 62.2%±4.4% vs 48.2%±4.1% (t=14.87, P＜0.01), fluorescence intensity: 4106±263 vs 2063±175 (t=17.49, P＜0.01). The treatment with 2-Me can reduce the antigenicity of JMH antigen on human RBC surface. The antigenicity of JMH antigen on human RBC surface increased after DTT treatment. The antigenicity of JMH antigen on human RBC surface significantly reduces after the treatment with pineapple protease or papain. ZZAP treatment can reduce the antigenicity of JMH antigen on the RBC surface.

Stimulating Effect of Manumycin A on Suicidal Erythrocyte Death

Background/Aims: The streptomycete derived farnesyltransferase inhibitor Manumycin A triggers apoptosis of tumor cells and is thus considered for the treatment of malignancy. The present study explored whether Manumycin A could similarly stimulate eryptosis, the suicidal death of erythrocytes characterized by cell shrinkage and cell membrane scrambling with phosphatidylserine translocation to the erythrocyte surface. Stimulators of eryptosis include Ca²⁺ entry as well as activation of staurosporine sensitive protein kinase C and SB203580 sensitive p38 kinase. The present study explored, whether Manumycin A induces eryptosis and, if so, to shed some light on the mechanisms involved. Methods: Phosphatidylserine abundance at the human erythrocyte surface was estimated from annexin-V-binding, cell volume from forward scatter, and hemolysis from hemoglobin concentration in the supernatant. Results: A 48 hours exposure of human erythrocytes to Manumycin A (≥ 5 µg/ml) significantly increased the percentage of annexin-V-binding cells, significantly decreased forward scatter and significantly incrased hemolysis. The effect of Manumycin A on annexin-V-binding was significantly blunted by removal of extracellular Ca²⁺, by addition of staurosporine (1 µM) and by addition of SB203580 (2 µM). Conclusions: Manumycin A triggers hemolysis, cell shrinkage and phospholipid scrambling of the human erythrocyte cell membrane. The effect on cell membrane scrambling was in part but not fully dependent on entry of extracellular Ca²⁺, as well as activity of staurosporine and SB203580 sensitive kinases.

Stimulating Effect of Terfenadine on Erythrocyte Cell Membrane Scrambling

Background/Aims: The antihistaminic drug Terfenadine may trigger apoptosis of tumor cells, an effect unrelated to its effect on histamine receptors. Similar to apoptosis of nucleated cells, erythrocytes may enter eryptosis, the suicidal death of erythrocytes characterized by cell shrinkage and cell membrane scrambling with phosphatidylserine translocation to the erythrocyte surface. Signaling triggering eryptosis include increase of cytosolic Ca²⁺ activity ([Ca²⁺]_i), oxidative stress, and ceramide. The present study explored, whether Terfenadine is capable to trigger eryptosis. Methods: Flow cytometry was employed to estimate phosphatidylserine abundance at the erythrocyte surface from annexin-V-binding, cell volume from forward scatter, [Ca²⁺]_i from Fluo3-fluorescence, abundance of reactive oxygen species (ROS) from 2′,7′-dichlorodihydrofluorescein (DCF) diacetate dependent fluorescence, and ceramide abundance at the human erythrocyte surface utilizing specific antibodies. Hemolysis was quantified from haemoglobin concentration in the supernatant. Results: A 48 hours exposure of human erythrocytes to Terfenadine (≥ 5 µM) significantly increased the percentage of annexin-V-binding cells and triggered hemolysis without significantly modifying the average forward scatter. Terfenadine (7.5 µM) significantly increased Fluo3-fluorescence, but did not significantly modify DCF fluorescence or ceramide abundance. The effect of Terfenadine on annexin-V-binding was significantly blunted but not abolished by removal of extracellular Ca²⁺. Exposure of human erythrocytes to Ca²⁺ ionophore ionomycin (1 µM, 15 min) triggered annexin-V-binding, an effect augmented by Terfenadine pretreatment (10 µM, 48 hours). Conclusions: Terfenadine triggers phospholipid scrambling of the human erythrocyte cell membrane, an effect in part due to entry of extracellular Ca²⁺ and in part due to sensitizing human erythrocyte cell membrane scrambling to Ca²⁺.

Human erythrocyte band 3 functions as a receptor for the sialic acid-independent invasion of Plasmodium falciparum. Role of the RhopH3–MSP1 complex

Plasmodium falciparum takes advantage of two broadly defined alternate invasion pathways when infecting human erythrocytes: one that depends on and the other that is independent of host sialic acid residues on the erythrocyte surface. Within the sialic acid-dependent (SAD) and sialic acid-independent (SAID) invasion pathways, several alternate host receptors are used by P. falciparum based on its particular invasion phenotype. Earlier, we reported that two putative extracellular regions of human erythrocyte band 3 termed 5C and 6A function as host invasion receptor segments binding parasite proteins MSP1 and MSP9 via a SAID mechanism. In this study, we developed two mono-specific anti-peptide chicken IgY antibodies to demonstrate that the 5C and 6A regions of band 3 are exposed on the surface of human erythrocytes. These antibodies inhibited erythrocyte invasion by the P. falciparum 3D7 and 7G8 strains (SAID invasion phenotype), and the blocking effect was enhanced in sialic acid-depleted erythrocytes. In contrast, the IgY antibodies had only a marginal inhibitory effect on FCR3 and Dd2 strains (SAD invasion phenotype). A direct biochemical interaction between erythrocyte band 3 epitopes and parasite RhopH3, identified by the yeast two-hybrid screen, was established. RhopH3 formed a complex with MSP119 and the 5ABC region of band 3, and a recombinant segment of RhopH3 inhibited parasite invasion in human erythrocytes. Together, these findings provide evidence that erythrocyte band 3 functions as a major host invasion receptor in the SAID invasion pathway by assembling a multi-protein complex composed of parasite ligands RhopH3 and MSP1.

A Human-Specific Mutation Limits Nonhuman Primate Efficacy in Preclinical Xenotransplantation Studies

Patients diagnosed with fulminant hepatic failure face high mortality rates. A potential therapeutic approach for these patients is the use of extracorporeal porcine liver perfusion, to serve as a form of "liver dialysis." Previously, our laboratory has shown that, during a 72-hour extracorporeal perfusion with human blood, porcine Kupffer cells bind to and phagocytose human erythrocytes causing the hematocrit to fall to 2.5% of the original value. Subsequently, erythrocyte binding has been shown to involve N-acetylneuraminic acid (Neu5Ac) on the surface of human erythrocytes and sialoadhesin on the surface of the porcine Kupffer cells. Given that no primate other than the human is known to express the majority of its sialic acid as Neu5Ac, we evaluated whether nonhuman primates would provide adequate evaluation of the loss of erythrocytes that might be expected in a clinical trial of extracorporeal porcine liver perfusion. We found that while porcine macrophages readily bound human erythrocytes, binding of nonhuman primate erythrocytes was significantly reduced (P<0.001). This study suggests that nonhuman primates may fail to serve as an adequate model for studying extracorporeal porcine liver perfusion because of the fact that porcine macrophages do not bind nonhuman primate erythrocytes.

The Epitope of Monoclonal Antibodies Blocking Erythrocyte Invasion by Plasmodium falciparum Map to The Dimerization and Receptor Glycan Binding Sites of EBA-175

The malaria parasite, Plasmodium falciparum, and related parasites use a variety of proteins with Duffy-Binding Like (DBL) domains to bind glycoproteins on the surface of host cells. Among these proteins, the 175 kDa erythrocyte binding antigen, EBA-175, specifically binds to glycophorin A on the surface of human erythrocytes during the process of merozoite invasion. The domain responsible for glycophorin A binding was identified as region II (RII) which contains two DBL domains, F1 and F2. The crystal structure of this region revealed a dimer that is presumed to represent the glycophorin A binding conformation as sialic acid binding sites and large cavities are observed at the dimer interface. The dimer interface is largely composed of two loops from within each monomer, identified as the F1 and F2 β-fingers that contact depressions in the opposing monomers in a similar manner. Previous studies have identified a panel of five monoclonal antibodies (mAbs) termed R215 to R218 and R256 that bind to RII and inhibit invasion of erythrocytes to varying extents. In this study, we predict the F2 β-finger region as the conformational epitope for mAbs, R215, R217, and R256, and confirm binding for the most effective blocking mAb R217 and R215 to a synthetic peptide mimic of the F2 β-finger. Localization of the epitope to the dimerization and glycan binding sites of EBA-175 RII and site-directed mutagenesis within the predicted epitope are consistent with R215 and R217 blocking erythrocyte invasion by Plasmodium falciparum by preventing formation of the EBA-175– glycophorin A complex.

Bacterial inclusion bodies as potential synthetic devices for pathogen recognition and a therapeutic substance release

BackgroundAdhesins of pathogens recognise the glycans on the host cell and mediate adherence. They are also crucial for determining the tissue preferences of pathogens. Currently, glyco-nanomaterials provide potential tool for antimicrobial therapy. We demonstrate that properly glyco-tailored inclusion bodies can specifically bind pathogen adhesins and release therapeutic substances.ResultsIn this paper, we describe the preparation of tailored inclusion bodies via the conjugation of indicator protein aggregated to form inclusion bodies with soluble proteins. Whereas the indicator protein represents a remedy, the soluble proteins play a role in pathogen recognition. For conjugation, glutaraldehyde was used as linker. The treatment of conjugates with polar lysine, which was used to inactivate the residual glutaraldehyde, inhibited unwanted hydrophobic interactions between inclusion bodies. The tailored inclusion bodies specifically interacted with the SabA adhesin from Helicobacter pylori aggregated to form inclusion bodies that were bound to the sialic acids decorating the surface of human erythrocytes. We also tested the release of indicator proteins from the inclusion bodies using sortase A and Ssp DNAB intein self-cleaving modules, respectively. Sortase A released proteins in a relatively short period of time, whereas the intein cleavage took several weeks.ConclusionsThe tailored inclusion bodies are promising “nanopills” for biomedical applications. They are able to specifically target the pathogen, while a self-cleaving module releases a soluble remedy. Various self-cleaving modules can be enabled to achieve the diverse pace of remedy release.

Interactions with heparin-like molecules during erythrocyte invasion by Plasmodium falciparum merozoites

AbstractDuring erythrocyte invasion, Plasmodium falciparum merozoites use multiple receptor-ligand interactions in a series of coordinated events, but current knowledge of these interactions is limited. Using real-time imaging of invasion, we established that heparin-like molecules block early, and essential, events in erythrocyte invasion by merozoites. All P falciparum isolates tested, and parasites using different invasion pathways were inhibited to comparable levels. Furthermore, it was not possible to select for heparin-resistant parasites. Heparin-like molecules occur naturally on the surface of human erythrocytes, where they may act as receptors for binding of merozoite surface proteins. Consistent with this, we demonstrated that MSP1-42, a processed form of merozoite surface protein 1 (MSP1) involved in invasion, bound heparin in a specific manner; furthermore, binding was observed with the secondary processing fragment MSP1-33, but not MSP1-19. We defined key structural requirements of heparin-like molecules for invasion inhibition and interactions with MSP1-42. Optimal activity required a degree of sulfation more than or equal to 2, disulfation of the N-acetylglucosamine or hexuronic acid residue, and a minimum chain length of 6 monosaccharides. These findings have significant implications for understanding P falciparum invasion of erythrocytes and the development of novel therapeutics and vaccines.

Structural insights into chondroitin sulphate A binding Duffy-binding-like domains from Plasmodium falciparum: implications for intervention strategies against placental malaria.

BackgroundPlacental malaria is typified by selective clustering of Plasmodium falciparum in the intervillous blood spaces of the placenta. Sequestration of malaria parasite in the human placenta is mediated by interactions between chondroitin sulphate A (CSA) on the syncytiotrophoblasts and proteins expressed on the surface of infected human erythrocytes. Plasmodium falciparum Erythrocyte Membrane Protein 1 (PfEMP1) encoded by the var2CSA gene is believed to be the main parasite ligand for CSA-mediated placental binding.MethodsExtensive sequence and structure comparisons of the various CSA-binding and non-binding DBL domains from the var2CSA gene from A4 and 3D7 strains of P. falciparum were performed. Three-dimensional structural models of various DBL domains were built and analysed with a view to assessing conservation of CSA interaction sites across various DBL domains.ResultsEach of the six DBL domains from var2CSA are likely to retain the disulfide linkages evident from previously published DBL domain crystal structures. The number of disulfide linkages between the various DBL domains analysed varies from three to seven, of which two are conserved across all DBL domains. The conserved disulfide linkages are distributed within the respective three sub-domains and only one linkage is shared by sub-domains I and II. Major differences between CSA-binding DBL domains are in the loop regions, which tie the alpha helices together, and in variable length terminal extensions. Intriguingly, a crucial loop from A4 DBL 3X which provides the important Gly and Lys residues that chelate the bound sulphate is missing or significantly altered in all other DBL domains that interact with CSA. Further analysis of the proposed sulphate and predicted CSA-binding site indicates either none or very low level of conservation among the critical interacting residues.ConclusionStructural comparisons of the three-dimensional structures of CSA-binding DBL domains indicates that the proposed CSA interaction site on A4 DBL 3X is unlikely to be conserved across the other CSA-binding DBL domains from var2CSA. Therefore, the 4 CSA-binding DBL domains encoded by var2CSA are unlikely to have common architectures to their CSA recognition sites. These structural insights have clear implications in using CSA-binding DBL domains for vaccines against placental malaria as it is proposed that the various CSA-binding DBL domains on var2CSA will recognize their CSA ligands differently.

Polymorphisms in erythrocyte binding antigens 140 and 181 affect function and binding but not receptor specificity in Plasmodium falciparum.

Invasion of human erythrocytes by the malaria parasite Plasmodium falciparum utilizes multiple ligand-receptor interactions involving erythrocyte receptors and parasite erythrocyte binding proteins of the Duffy binding-like family. Erythrocyte binding antigen 175 (EBA-175) binds to glycophorin A, the most abundant protein on the human erythrocyte surface and EBA-140 (also known as BAEBL) binds to glycophorin C, while the receptor for EBA-181 (also known as JESEBL) remains unknown. EBA binding is mediated via region II, a highly structured extracellular domain that shows a degree of sequence variability between different laboratory strains/isolates. Here, we determined the influence of region II polymorphisms on host cell receptor binding and overall function during invasion of EBA-140, EBA-175, and EBA-181. Polymorphisms in the binding domains of EBA-140 and EBA-181 have been suggested previously to alter their respective receptor specificities. In our hands, these polymorphisms affected the levels of EBA-140 and EBA-181 binding to receptors but, critically, not the receptor specificities of these proteins. The degree of EBA-140 binding to glycophorin C correlates with the level of function for this ligand-receptor interaction in merozoite invasion. In contrast, EBA-175, which is highly polymorphic in region II, shows no variability in its ability to bind to its receptor, glycophorin A. Combined, these data highlight the importance of sequence variability in EBAs as driven by immune selection but not by receptor specificity.

Erythrocyte Binding Protein PfRH5 Polymorphisms Determine Species-Specific Pathways of Plasmodium falciparum Invasion

Some human malaria Plasmodium falciparum parasites, but not others, also cause disease in Aotus monkeys. To identify the basis for this variation, we crossed two clones that differ in Aotus nancymaae virulence and mapped inherited traits of infectivity to erythrocyte invasion by linkage analysis. A major pathway of invasion was linked to polymorphisms in a putative erythrocyte binding protein, PfRH5, found in the apical region of merozoites. Polymorphisms of PfRH5 from the A. nancymaae-virulent parent transformed the nonvirulent parent to a virulent parasite. Conversely, replacements that removed these polymorphisms from PfRH5 converted a virulent progeny clone to a nonvirulent parasite. Further, a proteolytic fragment of PfRH5 from the infective parasites bound to A. nancymaae erythrocytes. Our results also suggest that PfRH5 is a parasite ligand for human infection, and that amino acid substitutions can cause its binding domain to recognize different human erythrocyte surface receptors.

Rosetting in Plasmodium falciparum: A cytoadherence phenotype with multiple actors

The capacity of Plasmodium falciparum-infected red blood cells to bind uninfected red blood cells (“rosetting”) has been associated with high parasite density in numerous geographic areas and with severe malaria in African children. We summarize here the associations that have emerged from field studies and describe the various experimental models of rosetting that have been developed. A variety of erythrocyte receptors, several serum factors and a number of rosette-mediating PfEMP1 adhesins have been identified. Several var genes code for rosette-forming PfEMP1 adhesins in each P. falciparum genome, so that each clonal line has the capacity to generate distinct types of rosettes. To clarify their respective role in malaria pathogenesis, each of the multiple ligand/receptor interactions should be further studied for fine specificity, binding affinity and the impact of the large population polymorphism of the parasite variant repertoires should be assessed. Interestingly, some major human erythrocyte surface polymorphisms have been identified as affecting rosette formation, consistent with a role for rosetting in life-threatening falciparum malaria.

The principle anion channel on P. falciparum ‐infected human erythrocytes is likely parasite‐encoded

The plasmodial surface anion channel (PSAC) is a voltage-dependent anion channel on the surface of human erythrocytes infected with Plasmodium falciparum. Electrophysiological studies from other groups suggest that the parasite may also induce additional ion channels, raising two important questions. First, which of these ion channels are responsible for parasite-induced increases in the permeabilities of needed solutes such as sugars, amino acids, purines, and organic cations? Second, does the uptake result from a parasite-encoded ion channel or does it result from modifications to host proteins? Here, we show that the parasite-induced permeabilities of two organic solutes, sorbitol and lactate, are inhibited by furosemide with a dose response precisely matching that for inhibition of PSAC-mediated currents, as detected with single molecule and whole-cell patch-clamp. PSAC activity was not affected by biochemical manipulations or by changes in host genetic factors such as a key CFTR mutation. We then explored PSAC’s origin with two geographically divergent parasite isolates cultured in human erythrocytes from the same donors. There were significant differences in the voltage-dependent gating behavior of PSAC that correlated with the parasite isolate used, but not with host genetic factors. PSAC also exhibits a unique pharmacological profile. Finally, unlike other anion channels, PSAC exhibits an unusual type of voltage-dependent inactivation that may be important for its function. Our findings suggest that PSAC is a parasite-encoded ion channel predominantly responsible for uptake of needed organic solutes and for removal of parasite metabolic waste products. PSAC’s unique functional and pharmacological properties implicate it as a novel target for antimalarial drug development.