Complement receptor 1 is the host erythrocyte receptor for Plasmodium falciparum PfRh4 invasion ligand

Plasmodium falciparum is responsible for the most severe form of malaria disease in humans, causing more than 1 million deaths each year. As an obligate intracellular parasite, P. falciparum’s ability to invade erythrocytes is essential for its survival within the human host. P. falciparum invades erythrocytes using multiple host receptor–parasite ligand interactions known as invasion pathways. Here we show that CR1 is the host erythrocyte receptor for PfRh4, a major P. falciparum ligand essential for sialic acid–independent invasion. PfRh4 and CR1 interact directly, with a K_d of 2.9 μM. PfRh4 binding is strongly correlated with the CR1 level on the erythrocyte surface. Parasite invasion via sialic acid–independent pathways is reduced in low-CR1 erythrocytes due to limited availability of this receptor on the surface. Furthermore, soluble CR1 can competitively block binding of PfRh4 to the erythrocyte surface and specifically inhibit sialic acid–independent parasite invasion. These results demonstrate that CR1 is an erythrocyte receptor used by the parasite ligand PfRh4 for P. falciparum invasion.     

Membrane specific mapping and colocalization of malarial and host skeletal proteins in the Plasmodium falciparum infected erythrocyte by dual-color near-field scanning optical microscopy

Accurate localization of proteins within the substructure of cells and cellular organelles enables better understanding of structure–function relationships, including elucidation of protein–protein interactions. We describe the use of a near-field scanning optical microscope (NSOM) to simultaneously map and detect colocalized proteins within a cell, with superresolution. The system we elected to study was that of human red blood cells invaded by the human malaria parasite Plasmodium falciparum. During intraerythrocytic growth, the parasite expresses proteins that are transported to the erythrocyte cell membrane. Association of parasite proteins with host skeletal proteins leads to modification of the erythrocyte membrane. We report on colocalization studies of parasite proteins with an erythrocyte skeletal protein. Host and parasite proteins were selectively labeled in indirect immunofluorescence antibody assays. Simultaneous dual-color excitation and detection with NSOM provided fluorescence maps together with topography of the cell membrane with subwavelength (100 nm) resolution. Colocalization studies with laser scanning confocal microscopy provided lower resolution (310 nm) fluorescence maps of cross sections through the cell. Because the two excitation colors shared the exact same near-field aperture, the two fluorescence images were acquired in perfect, pixel-by-pixel registry, free from chromatic aberrations, which contaminate laser scanning confocal microscopy measurements. Colocalization studies of the protein pairs of mature parasite-infected erythrocyte surface antigen (MESA)(parasite)/protein4.1(host) and P. falciparum histidine rich protein (PfHRP1)(parasite)/protein4.1(host) showed good real-space correlation for the MESA/protein4.1 pair, but relatively poor correlation for the PfHRP1/protein4.1 pair. These data imply that NSOM provides high resolution information on in situ interactions between proteins in biological membranes. This method of detecting colocalization of proteins in cellular structures may have general applicability in many areas of current biological research.     

Characterization of the Population Demographics and the MSP-1 Block 2 Allele Gene Frequencies of P. falciparum Infected Individuals in Davao,Philippines

Plasmodium falciparum is one of the causative agents of malaria in humans. This parasite causes the most severe forms of the disease. In order to combat the disease, it is important to have knowledge about the parasite and its interaction with its host. In this study, we profiled 74 patients admitted to hospital in Tagum, Davao, Philippines who were confirmed to be infected with P. falciparum. We correlated the age, sex and parasite load with malaria severity and show that among these, only sex is correlated with disease severity in this population. In addition, we profiled the MSP-1 block 2 allele distribution in the population and found that the most abundant allele form was K1, followed by MAD20. The RO33 allele form was the rarest allele in this population.     

Refractive index maps and membrane dynamics of human red blood cells parasitized by Plasmodium falciparum

Parasitization by malaria-inducing Plasmodium falciparum leads to structural, biochemical, and mechanical modifications to the host red blood cells (RBCs). To study these modifications, we investigate two intrinsic indicators: the refractive index and membrane fluctuations in P. falciparum-invaded human RBCs (Pf-RBCs). We report experimental connections between these intrinsic indicators and pathological states. By employing two noninvasive optical techniques, tomographic phase microscopy and diffraction phase microscopy, we extract three-dimensional maps of refractive index and nanoscale cell membrane fluctuations in isolated RBCs. Our systematic experiments cover all intraerythrocytic stages of parasite development under physiological and febrile temperatures. These findings offer potential, and sufficiently general, avenues for identifying, through cell membrane dynamics, pathological states that cause or accompany human diseases.     

African great apes are natural hosts of multiple related malaria species,including Plasmodium falciparum

Plasmodium reichenowi, a chimpanzee parasite, was until very recently the only known close relative of Plasmodium falciparum, the most virulent agent of human malaria. Recently, Plasmodium gaboni, another closely related chimpanzee parasite, was discovered, suggesting that the diversity of Plasmodium circulating in great apes in Africa might have been underestimated. It was also recently shown that P. reichenowi is a geographically widespread and genetically diverse chimpanzee parasite and that the world diversity of P. falciparum is fully included within the much broader genetic diversity of P. reichenowi. The evidence indicates that all extant populations of P. falciparum originated from P. reichenowi, likely by a single transfer from chimpanzees. In this work, we have studied the diversity of Plasmodium species infecting chimpanzees and gorillas in Central Africa (Cameroon and Gabon) from both wild-living and captive animals. The studies in wild apes used noninvasive sampling methods. We confirm the presence of P. reichenowi and P. gaboni in wild chimpanzees. Moreover, our results reveal the existence of an unexpected genetic diversity of Plasmodium lineages circulating in gorillas. We show that gorillas are naturally infected by two related lineages of parasites that have not been described previously, herein referred to as Plasmodium GorA and P. GorB, but also by P. falciparum, a species previously considered as strictly human specific. The continuously increasing contacts between humans and primate populations raise concerns about further reciprocal host transfers of these pathogens.     

Maurer's clefts,the enigma of Plasmodium falciparum

Plasmodium falciparum, the causative agent of malaria, completely remodels the infected human erythrocyte to acquire nutrients and to evade the immune system. For this process, the parasite exports more than 10% of all its proteins into the host cell cytosol, including the major virulence factor PfEMP1 (P. falciparum erythrocyte surface protein 1). This unusual protein trafficking system involves long-known parasite-derived membranous structures in the host cell cytosol, called Maurer’s clefts. However, the genesis, role, and function of Maurer’s clefts remain elusive. Similarly unclear is how proteins are sorted and how they are transported to and from these structures. Recent years have seen a large increase of knowledge but, as yet, no functional model has been established. In this perspective we review the most important findings and conclude with potential possibilities to shed light into the enigma of Maurer’s clefts. Understanding the mechanism and function of these structures, as well as their involvement in protein export in P. falciparum, might lead to innovative control strategies and might give us a handle with which to help to eliminate this deadly parasite.Since Charles Louis Alphonse Laveran discovered the malaria parasite in 1881 (1) in Algeria, while examining the blood of a patient who had died from marsh fever, research has been conducted on these deadly parasites. Laveran received the Nobel Prize in medicine for his discovery in 1907, which causally explained that malaria symptoms are caused by protozoan parasites, eventually described as Plasmodium species of the phylum Apicomplexa. Among the five species infecting humans, Plasmodium falciparum causes the most lethal forms of the disease, but zoonotic Plasmodium knowlesi infections can also be lethal.     

African apes as reservoirs of Plasmodium falciparum and the origin and diversification of the Laverania subgenus

We investigated two mitochondrial genes (cytb and cox1), one plastid gene (tufA), and one nuclear gene (ldh) in blood samples from 12 chimpanzees and two gorillas from Cameroon and one lemur from Madagascar. One gorilla sample is related to Plasmodium falciparum, thus confirming the recently reported presence in gorillas of this parasite. The second gorilla sample is more similar to the recently defined Plasmodium gaboni than to the P. falciparum–Plasmodium reichenowi clade, but distinct from both. Two chimpanzee samples are P. falciparum. A third sample is P. reichenowi and two others are P. gaboni. The other chimpanzee samples are different from those in the ape clade: two are Plasmodium ovale, and one is Plasmodium malariae. That is, we have found three human Plasmodium parasites in chimpanzees. Four chimpanzee samples were mixed: one species was P. reichenowi; the other species was P. gaboni in three samples and P. ovale in the fourth sample. The lemur sample, provisionally named Plasmodium malagasi, is a sister lineage to the large cluster of primate parasites that does not include P. falciparum or ape parasites, suggesting that the falciparum + ape parasite cluster (Laverania clade) may have evolved from a parasite present in hosts not ancestral to the primates. If malignant malaria were eradicated from human populations, chimpanzees, in addition to gorillas, might serve as a reservoir for P. falciparum.     

Small-molecule histone methyltransferase inhibitors display rapid antimalarial activity against all blood stage forms in Plasmodium falciparum

Epigenetic factors such as histone methylation control the developmental progression of malaria parasites during the complex life cycle in the human host. We investigated Plasmodium falciparum histone lysine methyltransferases as a potential target class for the development of novel antimalarials. We synthesized a compound library based upon a known specific inhibitor (BIX-01294) of the human G9a histone methyltransferase. Two compounds, BIX-01294 and its derivative TM2-115, inhibited P. falciparum 3D7 parasites in culture with IC₅₀ values of ∼100 nM, values at least 22-fold more potent than their apparent IC₅₀ toward two human cell lines and one mouse cell line. These compounds irreversibly arrested parasite growth at all stages of the intraerythrocytic life cycle. Decrease in parasite viability (>40%) was seen after a 3-h incubation with 1 µM BIX-01294 and resulted in complete parasite killing after a 12-h incubation. Additionally, mice with patent Plasmodium berghei ANKA strain infection treated with a single dose (40 mg/kg) of TM2-115 had 18-fold reduced parasitemia the following day. Importantly, treatment of P. falciparum parasites in culture with BIX-01294 or TM2-115 resulted in significant reductions in histone H3K4me3 levels in a concentration-dependent and exposure time-dependent manner. Together, these results suggest that BIX-01294 and TM2-115 inhibit malaria parasite histone methyltransferases, resulting in rapid and irreversible parasite death. Our data position histone lysine methyltransferases as a previously unrecognized target class, and BIX-01294 as a promising lead compound, in a presently unexploited avenue for antimalarial drug discovery targeting multiple life-cycle stages.     

Plasmodium falciparum var gene expression is modified by host immunity

Plasmodium falciparum erythrocyte membrane protein 1 (PfEMP1) is a potentially important family of immune targets, which play a central role in the host–parasite interaction by binding to various host molecules. They are encoded by a diverse family of genes called var, of which there are ≈60 copies in each parasite genome. In sub-Saharan Africa, although P. falciparum infection occurs throughout life, severe malarial disease tends to occur only in childhood. This could potentially be explained if (i) PfEMP1 variants differ in their capacity to support pathogenesis of severe malaria and (ii) this capacity is linked to the likelihood of each molecule being recognized and cleared by naturally acquired antibodies. Here, in a study of 217 Kenyan children with malaria, we show that expression of a group of var genes “cys2,” containing a distinct pattern of cysteine residues, is associated with low host immunity. Expression of cys2 genes was associated with parasites from young children, those with severe malaria, and those with a poorly developed antibody response to parasite-infected erythrocyte surface antigens. Cys-2 var genes form a minor component of all genomic var repertoires analyzed to date. Therefore, the results are compatible with the hypothesis that the genomic var gene repertoire is organized such that PfEMP1 molecules that confer the most virulence to the parasite tend also to be those that are most susceptible to the development of host immunity. This may help the parasite to adapt effectively to the development of host antibodies through modification of the host–parasite relationship.     

Oxidative damage of erythrocytes infected with Plasmodium falciparum

Summary The extent of reduced glutathione, activity of glutathione peroxidase, amount of membrane lipid peroxidation products, and the extent of hemoglobin release from host erythrocytes during in vitroPlasmodium falciparum growth was studied. Highly synchronized parasite cultures were studied to examine the alterations caused by different growth stages of the parasite. There was a moderate increase in the reduced glutathione content as the parasite matured, which was significant only in schizontrich erythrocyte lysates (p<0.05) whereas the activity of glutathione peroxidase was significantly low in all the parasitized red blood cells (ring-infected RBC,p<0.005; trophozoite- and schizont-infected RBC,p<0.001). The lipid peroxidation product, malonyldialdehyde, of the host red cells increased gradually to more than fourfold in schizont-rich cells as compared with normal erythrocytes (p<0.001). The hemoglobin release from cultured cells was significantly higher in all parasitized red cell cultures as well as in uninfected cells kept in in vitro, as compared with normal erythrocytes. The consequence of such changes induced by the malarial parasites in the host red cells in the pathogenesis of erythrocyte destruction and anemia ofP. falciparum malaria is discussed.     

Malaria: modification of the red blood cell and consequences in the human host

Residence in the human erythrocyte is essential for the lifecycle of all Plasmodium that infect man. It is also the phase of the life cycle that causes disease. Although the red blood cell (RBC) is a highly specialized cell for its function of carrying oxygen to and carbon dioxide away from tissues, it is devoid of organelles and lacks any cellular machinery to synthesize new protein. Therefore in order to be able to survive and multiply within the RBC membrane the parasite needs to make many modifications to the infected RBC (iRBC). Plasmodium falciparum (P. falciparum) also expresses parasite‐derived proteins on the surface of the iRBC that enable the parasite to cytoadhere to endothelial and other intravascular cells. These RBC modifications are at the root of malaria pathogenesis and, in this ancient disease of man, have formed the epicentre of a genetic ‘battle’ between parasite and host. This review discusses some of the critical modifications of the RBC by the parasite and some of the consequences of these adaptations on disease in the human host, with an emphasis on advances in understanding of the pathogenesis of severe and cerebral malaria (CM) from recent research.     

Plasmodium evasion of mosquito immunity and global malaria transmission: The lock-and-key theory

Plasmodium falciparum malaria originated in Africa and became global as humans migrated to other continents. During this journey, parasites encountered new mosquito species, some of them evolutionarily distant from African vectors. We have previously shown that the Pfs47 protein allows the parasite to evade the mosquito immune system of Anopheles gambiae mosquitoes. Here, we investigated the role of Pfs47-mediated immune evasion in the adaptation of P. falciparum to evolutionarily distant mosquito species. We found that P. falciparum isolates from Africa, Asia, or the Americas have low compatibility to malaria vectors from a different continent, an effect that is mediated by the mosquito immune system. We identified 42 different haplotypes of Pfs47 that have a strong geographic population structure and much lower haplotype diversity outside Africa. Replacement of the Pfs47 haplotypes in a P. falciparum isolate is sufficient to make it compatible to a different mosquito species. Those parasites that express a Pfs47 haplotype compatible with a given vector evade antiplasmodial immunity and survive. We propose that Pfs47-mediated immune evasion has been critical for the globalization of P. falciparum malaria as parasites adapted to new vector species. Our findings predict that this ongoing selective force by the mosquito immune system could influence the dispersal of Plasmodium genetic traits and point to Pfs47 as a potential target to block malaria transmission. A new model, the “lock-and-key theory” of P. falciparum globalization, is proposed, and its implications are discussed.The most deadly form of malaria in humans is caused by Plasmodium falciparum parasites. Malaria originated in Africa (1, 2) and is transmitted by anopheline mosquitoes. The disease became global as humans migrated to other continents and parasites encountered different mosquito species that were sometimes evolutionarily distant from African vectors (3). For example, anophelines of the subgenus Nyssorhynchus (malaria vectors in Central and South America, such as Anopheles albimanus) diverged from the subgenus Cellia (malaria vectors in Africa, India, and South Asia) about 100 Mya (4). P. falciparum parasites are transmitted by more than 70 different anopheline species worldwide (3), but compatibilities differ between specific vector–parasite combinations (5). For example, P. falciparum NF54 (Pf NF54), of putative African origin, effectively infects Anopheles gambiae, the main malaria vector in sub-Saharan Africa; but A. albimanus is highly refractory to this strain (6–8); whereas Asian P. falciparum isolates infect Anopheles stephensi (Nijmegen strain), a major vector in India, more effectively than A. gambiae (9). Similar differences in compatibility have been reported between Plasmodium vivax and different anopheline species (10, 11). The A. gambiae immune system can mount effective antiplasmodial responses mediated by the complement-like system that limit infection (12). We have previously shown that some P. falciparum lines can avoid detection by the A. gambiae immune system (13) and identified Pfs47 as the gene that mediated immune evasion (14). Here, we present direct evidence of selection of P. falciparum by the mosquito immune system and show that providing P. falciparum with a Pfs47 haplotype compatible for a given anopheline mosquito is sufficient for the parasite to evade mosquito immunity. The implications of P. falciparum selection by mosquitoes for global malaria transmission are discussed.     

Recombinant viruses expressing a human malaria antigen can elicit potentially protective immune CD8+ responses in mice

Extensive studies on protective immunity to rodent malaria provided the basis for the current experiments in which mice were immunized with recombinant (re) influenza and vaccinia viruses expressing selected sequences of the circumsporozoite (CS) protein of the human malaria parasite Plasmodium falciparum. Mice of different H-2 haplotypes immunized with re influenza viruses expressing the immunodominant B cell epitope of this CS protein produced high titers of antibodies to the parasite. A cytotoxic T lymphocyte epitope of the CS protein of P. falciparum, PF3, recognized by CD8⁺ T cells of H-2^k mice, was expressed in a re vaccinia virus (VacPf) and a re influenza virus (FluPf). Immunization of mice with either FluPf or VacPf elicited a modest CS-specific CD8⁺ T cell response detected by interferon γ secretion of individual immune cells. Priming of mice with FluPf, followed by a booster with VacPf, resulted in a striking enhancement of this T cell response. The reverse protocol, i.e., priming with VacPf followed by a booster with FluPf, failed to enhance the primary response. VacPf also greatly enhanced the primary response of mice injected with P. falciparum sporozoites or with a lipopeptide containing PF3. A booster with FluPf also amplified the response of lipopeptide- or sporozoite-primed mice but less than a VacPf booster did. Although mice are not susceptible to infection by P. falciparum sporozoites, we demonstrated that administration of two distinct immunogens expressing PF3 elicited activated, extravasating CS-specific T cells that protected against an intracerebral VacPf challenge.     

Multiprotein complex between the GPI-anchored CyRPA with PfRH5 and PfRipr is crucial for Plasmodium falciparum erythrocyte invasion

Erythrocyte invasion by Plasmodium falciparum merozoites is a highly intricate process in which Plasmodium falciparum reticulocyte binding-like homologous protein 5 (PfRH5) is an indispensable parasite ligand that binds with its erythrocyte receptor, Basigin. PfRH5 is a leading blood-stage vaccine candidate because it exhibits limited polymorphisms and elicits potent strain-transcending parasite neutralizing antibodies. However, the mechanism by which it is anchored to the merozoite surface remains unknown because both PfRH5 and the PfRH5-interacting protein (PfRipr) lack transmembrane domains and GPI anchors. Here we have identified a conserved GPI-linked parasite protein, Cysteine-rich protective antigen (CyRPA) as an interacting partner of PfRH5-PfRipr that tethers the PfRH5/PfRipr/CyRPA multiprotein complex on the merozoite surface. CyRPA was demonstrated to be GPI-linked, localized in the micronemes, and essential for erythrocyte invasion. Specific antibodies against the three proteins successfully detected the intact complex in the parasite and coimmunoprecipitated the three interacting partners. Importantly, full-length CyRPA antibodies displayed potent strain-transcending invasion inhibition, as observed for PfRH5. CyRPA does not bind with erythrocytes, suggesting that its parasite neutralizing antibodies likely block its critical interaction with PfRH5-PfRipr, leading to a blockade of erythrocyte invasion. Further, CyRPA and PfRH5 antibody combinations produced synergistic invasion inhibition, suggesting that simultaneous blockade of the PfRH5–Basigin and PfRH5/PfRipr/CyRPA interactions produced an enhanced inhibitory effect. Our discovery of the critical interactions between PfRH5, PfRipr, and the GPI-anchored CyRPA clearly defines the components of the essential PfRH5 adhesion complex for P. falciparum erythrocyte invasion and offers it as a previously unidentified potent target for antimalarial strategies that could abrogate formation of the crucial multiprotein complex.Erythrocyte invasion by Plasmodium falciparum merozoites is crucial for malaria pathogenesis, and thus the parasite has evolved an extensive molecular machinery to ensure invasion through multiple pathways (1–3). The quest to develop successful blood-stage malaria vaccines that efficiently block this process have focused on essential parasite proteins like merozoite surface protein 1 (MSP-1) and apical membrane antigen 1 (AMA-1); however, these are highly polymorphic, unable to elicit strain-transcending neutralizing antibodies, and have thus failed in field trials (4). Among the large repertoire of invasion-related proteins, the family of P. falciparum reticulocyte binding-like homologous (PfRH) proteins have emerged as key determinants of different invasion pathways (2, 3), of which PfRH5 is the only essential conserved parasite ligand (5–8) that elicits potent strain-transcending neutralizing antibodies (9–12). It is localized in the rhoptry and secreted to the merozoite surface during erythrocyte invasion (6). It does not seem to be under immune pressure (9, 13) and is favored to be a leading vaccine candidate. PfRH5 has been shown to interact with another parasite protein, PfRipr (P. falciparum RH5 interacting protein) (14). However, both these proteins lack transmembrane domains as well as a GPI anchor, and thus the mechanism through which PfRH5 is secured on the surface of an invading merozoite to facilitate its functional role during invasion still remains unknown. It is likely that PfRH5 might be attached to the merozoite surface as a complex with other essential proteins other than PfRipr, identification of which could open new therapeutic avenues against malaria.Here we show that PfRH5 and PfRipr interact with a GPI-linked parasite protein, CyRPA (Cysteine-rich protective antigen) (15) to form an essential complex on the surface of an invading merozoite. Individual antibodies against each of the three proteins successfully coimmunoprecipitated all three proteins, confirming their presence as a multiprotein complex. Analysis of the native parasite protein complex by different chromatographic techniques further confirmed that all three protein components coeluted together and were present as a much higher molecular mass species than their individual molecular masses. We also demonstrated that the three proteins are colocalized on the apical surface of the invading merozoite, of which only CyRPA was shown to be GPI-linked. Importantly, antibodies against full-length CyRPA potently blocked erythrocyte invasion by multiple P. falciparum strains, as observed previously only for PfRH5 antibodies (9–12). Because CyRPA does not bind with the erythrocyte surface, it seems that the parasite-neutralizing CyRPA antibodies function by impeding its interaction with PfRH5 or PfRipr. Hence, we have identified and validated a GPI-linked parasite protein, CyRPA, as another essential interacting partner of PfRH5 that is responsible for tethering it to the merozoite surface. Further, we have shown that like PfRH5, CyRPA is a conserved target of potent antibody-mediated blockade of erythrocyte invasion and thus seems to be another highly promising blood-stage vaccine candidate.     

PCR扩增环子孢子蛋白基因3’ 端片段用于检测恶性疟原虫的初步研究

目的 :建立 PCR检测恶性疟原虫的新方法。方法 :作者采用自行设计并合成的一对恶性疟原虫特异引物 ,经 PCR扩增环子孢子蛋白 ( CSP)基因 3 端保守区序列 2 4 5bp片段 ,观察了它的特异性、敏感性和稳定性。结果 :1从 4株培养的恶性疟原虫和 2例恶性疟患者血样中均扩增出约 2 4 5bp的 DNA目的片段 ,用业已鉴定的 CSP基因序列作模板再行扩增证实其为恶性疟原虫CSP基因片段 ;2对间日疟原虫、利什曼原虫、弓形虫和健康人血样进行 PCR反应 ,均未见扩增条带 ;3本检测系统可检出恶性疟原虫感染血样中 0 .18个原虫所含的 DNA模板 ;4采用不同方法制备模板及不同反应方式均能获得满意结果 ;结论 :PCR扩增恶性疟原虫 CSP基因 3端片段用于恶性疟原虫检测具有灵敏、高度特异且稳定性好等优点。     

Trypanosoma cruzi nucleoside triphosphate diphosphohydrolase 1 (TcNTPDase-1) biochemical characterization,immunolocalization and possible role in host cell adhesion

Previous work has suggested that Trypanosoma cruzi diphosphohydrolase 1 (TcNTPDase-1) may be involved in the infection of mammalian cells and serve as a potential target for rational drug design. In this work, we produced recombinant TcNTPDase-1 and evaluated its nucleotidase activity, cellular localization and role in parasite adhesion to mammalian host cells. TcNTPDase-1 was able to utilize a broad range of triphosphate and diphosphate nucleosides. The enzyme's K_m for ATP (0.096 mM) suggested a capability to influence the host's ATP-dependent purinergic signaling. The use of specific polyclonal antibodies allowed us to confirm the presence of TcNTPDase-1 at the surface of parasites by confocal and electron microscopy. In addition, electron microscopy revealed that TcNTPDase-1 was also found in the flagellum, flagellum insertion region, kinetoplast, nucleus and intracellular vesicles. The presence of this enzyme in the flagellum insertion region and vesicles suggests that it may have a role in nutrient acquisition, and the widespread distribution of TcNTPDase-1 within the parasite suggests that it may be involved in other biological process. Adhesion assays using anti-TcNTPDase-1 polyclonal antibodies as a blocker or purified recombinant TcNTPDase-1 as a competitor revealed that the enzyme has a role in parasite–host cell adhesion. These data open new frontiers to future studies on this specific parasite–host interaction and other unknown functions of TcNTPDase-1 related to its ubiquitous localization.     

A redox-sensitive peroxiredoxin that is important for longevity has tissue- and stress-specific roles in stress resistance

Oxidative damage caused by reactive oxygen species (ROS) is implicated in many diseases and in aging. Removal of ROS by antioxidant enzymes plays an important part in limiting this damage. For instance, peroxiredoxins (Prx) are conserved, abundant, thioredoxin peroxidase enzymes that function as tumor suppressors. In addition to detoxifying peroxides, studies in single-cell systems have revealed that Prx act as chaperones and redox sensors. However, it is unknown in what manner the different activities of Prx influence stress resistance or longevity in the context of whole animals. Here, we reveal three distinct roles for the 2-Cys Prx, PRDX-2, in the stress resistance of the nematode worm Caenorhabditis elegans. (i) The thioredoxin peroxidase activity of PRDX-2 protects against hydrogen peroxide. (ii) Consistent with a chaperone activity for hyperoxidized PRDX-2, peroxide-induced oxidation of PRDX-2 increases resistance to heat stress. (iii) Unexpectedly, loss of PRDX-2 increases the resistance of C. elegans to some oxidative stress-causing agents, such as arsenite, apparently through a signaling mechanism that increases the levels of other antioxidants and phase II detoxification enzymes. Despite their increased resistance to some forms of oxidative stress, prdx-2 mutants are short-lived. Moreover, intestinal expression of PRDX-2 accounts for its role in detoxification of exogenous peroxide, but not its influence on either arsenite resistance or longevity, suggesting that PRDX-2 may promote longevity and protect against environmental stress through different mechanisms. Together the data reveal that in metazoans Prx act through multiple biochemical activities, and have tissue-specific functions in stress resistance and longevity.     

Evaluation of the NOW Malaria Immunochromatographic Test for Quantitative Diagnosis of Falciparum and Vivax Malaria Parasite Density

The NOW® Malaria Test, an immunochromatographic test (ICT), was evaluated to determine its ability to quantitatively detect malaria parasites using 100 blood samples from Thailand, including 50 Plasmodium falciparum (Pf) infections and 50 P. vivax (Pv) infections. Intensities of the thickness of the visible bands of the positive ICT were compared with the parasite densities. In cases of Pf infection, the intensities of both HRP-2 bands (T1 bands: Pf specific bands) and aldolase bands (T2 bands: pan-Plasmodium bands) correlated with the parasite densities. The intensities of T2 bands in Pf positive samples showed better correlation with the parasite densities than the T1 bands. In the cases of Pv infection, the intensities of T2 bands were also well correlated with parasite density. These results suggest that the ICT is useful not only for rapid detection of malaria parasites but also for estimating parasite density.     

Host density drives the postglacial migration of the tree parasite,Epifagus virginiana

To survive changes in climate, successful species shift their geographic ranges to remain in suitable habitats. For parasites and other highly specialized species, distributional changes not only are dictated by climate but can also be engineered by their hosts. The extent of host control on parasite range expansion is revealed through comparisons of host and parasite migration and demographic histories. However, understanding the codistributional history of entire forest communities is complicated by challenges in synthesizing datasets from multiple interacting species of differing datatypes. Here we integrate genetic and fossil pollen datasets from a host–parasite pair; specifically, the population structure of the parasitic plant (Epifagus virginiana) was compared with both its host (Fagus grandifolia) genetic patterns and abundance data from the paleopollen record of the last 21,000 y. Through tests of phylogeographic structure and spatial linear regression models we find, surprisingly, host range changes had little effect on the parasite''s range expansion and instead host density is the main driver of parasite spread. Unlike other symbionts that have been used as proxies to track their host''s movements, this parasite''s migration routes are incongruent with the host and instead reflect the greater importance of host density in this community''s assembly. Furthermore, these results confirm predictions of disease ecological models regarding the role of host density in the spread of pathogens. Due to host density constraints, highly specialized species may have low migration capacities and long lag times before colonization of new areas.