Disease progression in Plasmodium knowlesi malaria is linked to variation in invasion gene family members.

Emerging pathogens undermine initiatives to control the global health impact of infectious diseases. Zoonotic malaria is no exception. Plasmodium knowlesi, a malaria parasite of Southeast Asian macaques, has entered the human population. P. knowlesi, like Plasmodium falciparum, can reach high parasitaemia in human infections, and the World Health Organization guidelines for severe malaria list hyperparasitaemia among the measures of severe malaria in both infections. Not all patients with P. knowlesi infections develop hyperparasitaemia, and it is important to determine why. Between isolate variability in erythrocyte invasion, efficiency seems key. Here we investigate the idea that particular alleles of two P. knowlesi erythrocyte invasion genes, P. knowlesi normocyte binding protein Pknbpxa and Pknbpxb, influence parasitaemia and human disease progression. Pknbpxa and Pknbpxb reference DNA sequences were generated from five geographically and temporally distinct P. knowlesi patient isolates. Polymorphic regions of each gene (approximately 800 bp) were identified by haplotyping 147 patient isolates at each locus. Parasitaemia in the study cohort was associated with markers of disease severity including liver and renal dysfunction, haemoglobin, platelets and lactate, (r = ≥ 0.34, p =  <0.0001 for all). Seventy-five and 51 Pknbpxa and Pknbpxb haplotypes were resolved in 138 (94%) and 134 (92%) patient isolates respectively. The haplotypes formed twelve Pknbpxa and two Pknbpxb allelic groups. Patients infected with parasites with particular Pknbpxa and Pknbpxb alleles within the groups had significantly higher parasitaemia and other markers of disease severity. Our study strongly suggests that P. knowlesi invasion gene variants contribute to parasite virulence. We focused on two invasion genes, and we anticipate that additional virulent loci will be identified in pathogen genome-wide studies. The multiple sustained entries of this diverse pathogen into the human population must give cause for concern to malaria elimination strategists in the Southeast Asian region

Sour Taste Responses in Mice Lacking PKD Channels

The polycystic kidney disease-like ion channel PKD2L1 and its associated partner PKD1L3 are potential candidates for sour taste receptors. PKD2L1 is expressed in type III taste cells that respond to sour stimuli and genetic elimination of cells expressing PKD2L1 substantially reduces chorda tympani nerve responses to sour taste stimuli. However, the contribution of PKD2L1 and PKD1L3 to sour taste responses remains unclear.We made mice lacking PKD2L1 and/or PKD1L3 gene and investigated whole nerve responses to taste stimuli in the chorda tympani or the glossopharyngeal nerve and taste responses in type III taste cells. In mice lacking PKD2L1 gene, chorda tympani nerve responses to sour, but not sweet, salty, bitter, and umami tastants were reduced by 25–45% compared with those in wild type mice. In contrast, chorda tympani nerve responses in PKD1L3 knock-out mice and glossopharyngeal nerve responses in single- and double-knock-out mice were similar to those in wild type mice. Sour taste responses of type III fungiform taste cells (GAD67-expressing taste cells) were also reduced by 25–45% by elimination of PKD2L1.These findings suggest that PKD2L1 partly contributes to sour taste responses in mice and that receptors other than PKDs would be involved in sour detection

An EGF-like Protein Forms a Complex with PfRh5 and Is Required for Invasion of Human Erythrocytes by Plasmodium falciparum

Invasion of erythrocytes by Plasmodium falciparum involves a complex cascade of protein-protein interactions between parasite ligands and host receptors. The reticulocyte binding-like homologue (PfRh) protein family is involved in binding to and initiating entry of the invasive merozoite into erythrocytes. An important member of this family is PfRh5. Using ion-exchange chromatography, immunoprecipitation and mass spectroscopy, we have identified a novel cysteine-rich protein we have called P. falciparum Rh5 interacting protein (PfRipr) (PFC1045c), which forms a complex with PfRh5 in merozoites. Mature PfRipr has a molecular weight of 123 kDa with 10 epidermal growth factor-like domains and 87 cysteine residues distributed along the protein. In mature schizont stages this protein is processed into two polypeptides that associate and form a complex with PfRh5. The PfRipr protein localises to the apical end of the merozoites in micronemes whilst PfRh5 is contained within rhoptries and both are released during invasion when they form a complex that is shed into the culture supernatant. Antibodies to PfRipr1 potently inhibit merozoite attachment and invasion into human red blood cells consistent with this complex playing an essential role in this process

Complement Receptor 1 Is a Sialic Acid-Independent Erythrocyte Receptor of Plasmodium falciparum

Plasmodium falciparum is a highly lethal malaria parasite of humans. A major portion of its life cycle is dedicated to invading and multiplying inside erythrocytes. The molecular mechanisms of erythrocyte invasion are incompletely understood. P. falciparum depends heavily on sialic acid present on glycophorins to invade erythrocytes. However, a significant proportion of laboratory and field isolates are also able to invade erythrocytes in a sialic acid-independent manner. The identity of the erythrocyte sialic acid-independent receptor has been a mystery for decades. We report here that the complement receptor 1 (CR1) is a sialic acid-independent receptor for the invasion of erythrocytes by P. falciparum. We show that soluble CR1 (sCR1) as well as polyclonal and monoclonal antibodies against CR1 inhibit sialic acid-independent invasion in a variety of laboratory strains and wild isolates, and that merozoites interact directly with CR1 on the erythrocyte surface and with sCR1-coated microspheres. Also, the invasion of neuraminidase-treated erythrocytes correlates with the level of CR1 expression. Finally, both sialic acid-independent and dependent strains invade CR1 transgenic mouse erythrocytes preferentially over wild-type erythrocytes but invasion by the latter is more sensitive to neuraminidase. These results suggest that both sialic acid-dependent and independent strains interact with CR1 in the normal red cell during the invasion process. However, only sialic acid-independent strains can do so without the presence of glycophorin sialic acid. Our results close a longstanding and important gap in the understanding of the mechanism of erythrocyte invasion by P. falciparum that will eventually make possible the development of an effective blood stage vaccine

Plasmodium falciparum Reticulocyte Binding-Like Homologue Protein 2 (PfRH2) Is a Key Adhesive Molecule Involved in Erythrocyte Invasion

Erythrocyte invasion by Plasmodium merozoites is a complex, multistep process that is mediated by a number of parasite ligand-erythrocyte receptor interactions. One such family of parasite ligands includes the P. falciparum reticulocyte binding homologue (PfRH) proteins that are homologous with the P. vivax reticulocyte binding proteins and have been shown to play a role in erythrocyte invasion. There are five functional PfRH proteins of which only PfRH2a/2b have not yet been demonstrated to bind erythrocytes. In this study, we demonstrated that native PfRH2a/2b is processed near the N-terminus yielding fragments of 220 kDa and 80 kDa that exhibit differential erythrocyte binding specificities. The erythrocyte binding specificity of the 220 kDa processed fragment of native PfRH2a/2b was sialic acid-independent, trypsin resistant and chymotrypsin sensitive. This specific binding phenotype is consistent with previous studies that disrupted the PfRH2a/2b genes and demonstrated that PfRH2b is involved in a sialic acid independent, trypsin resistant, chymotrypsin sensitive invasion pathway. Interestingly, we found that the smaller 80 kDa PfRH2a/2b fragment is processed from the larger 220 kDa fragment and binds erythrocytes in a sialic acid dependent, trypsin resistant and chymotrypsin sensitive manner. Thus, the two processed fragments of PfRH2a/2b differed with respect to their dependence on sialic acids for erythrocyte binding. Further, we mapped the erythrocyte binding domain of PfRH2a/2b to a conserved 40 kDa N-terminal region (rPfRH240) in the ectodomain that is common to both PfRH2a and PfRH2b. We demonstrated that recombinant rPfRH240 bound human erythrocytes with the same specificity as the native 220 kDa processed protein. Moreover, antibodies generated against rPfRH240 blocked erythrocyte invasion by P. falciparum through a sialic acid independent pathway. PfRH2a/2b thus plays a key role in erythrocyte invasion and its conserved receptor-binding domain deserves attention as a promising candidate for inclusion in a blood-stage malaria vaccine

Sour Ageusia in Two Individuals Implicates Ion Channels of the ASIC and PKD Families in Human Sour Taste Perception at the Anterior Tongue

BACKGROUND:The perception of sour taste in humans is incompletely understood at the receptor cell level. We report here on two patients with an acquired sour ageusia. Each patient was unresponsive to sour stimuli, but both showed normal responses to bitter, sweet, and salty stimuli. METHODS AND FINDINGS:Lingual fungiform papillae, containing taste cells, were obtained by biopsy from the two patients, and from three sour-normal individuals, and analyzed by RT-PCR. The following transcripts were undetectable in the patients, even after 50 cycles of amplification, but readily detectable in the sour-normal subjects: acid sensing ion channels (ASICs) 1a, 1beta, 2a, 2b, and 3; and polycystic kidney disease (PKD) channels PKD1L3 and PKD2L1. Patients and sour-normals expressed the taste-related phospholipase C-beta2, the delta-subunit of epithelial sodium channel (ENaC) and the bitter receptor T2R14, as well as beta-actin. Genomic analysis of one patient, using buccal tissue, did not show absence of the genes for ASIC1a and PKD2L1. Immunohistochemistry of fungiform papillae from sour-normal subjects revealed labeling of taste bud cells by antibodies to ASICs 1a and 1beta, PKD2L1, phospholipase C-beta2, and delta-ENaC. An antibody to PKD1L3 labeled tissue outside taste bud cells. CONCLUSIONS:These data suggest a role for ASICs and PKDs in human sour perception. This is the first report of sour ageusia in humans, and the very existence of such individuals ("natural knockouts") suggests a cell lineage for sour that is independent of the other taste modalities

Plasmodium falciparum Merozoite Invasion Is Inhibited by Antibodies that Target the PfRh2a and b Binding Domains

Plasmodium falciparum, the causative agent of the most severe form of malaria in humans invades erythrocytes using multiple ligand-receptor interactions. The P. falciparum reticulocyte binding-like homologue proteins (PfRh or PfRBL) are important for entry of the invasive merozoite form of the parasite into red blood cells. We have analysed two members of this protein family, PfRh2a and PfRh2b, and show they undergo a complex series of proteolytic cleavage events before and during merozoite invasion. We show that PfRh2a undergoes a cleavage event in the transmembrane region during invasion consistent with activity of the membrane associated PfROM4 protease that would result in release of the ectodomain into the supernatant. We also show that PfRh2a and PfRh2b bind to red blood cells and have defined the erythrocyte-binding domain to a 15 kDa region at the N-terminus of each protein. Antibodies to this receptor-binding region block merozoite invasion demonstrating the important function of this domain. This region of PfRh2a and PfRh2b has potential in a combination vaccine with other erythrocyte binding ligands for induction of antibodies that would block a broad range of invasion pathways for P. falciparum into human erythrocytes

Copying and Evolution of Neuronal Topology

We propose a mechanism for copying of neuronal networks that is of considerable interest for neuroscience for it suggests a neuronal basis for causal inference, function copying, and natural selection within the human brain. To date, no model of neuronal topology copying exists. We present three increasingly sophisticated mechanisms to demonstrate how topographic map formation coupled with Spike-Time Dependent Plasticity (STDP) can copy neuronal topology motifs. Fidelity is improved by error correction and activity-reverberation limitation. The high-fidelity topology-copying operator is used to evolve neuronal topologies. Possible roles for neuronal natural selection are discussed