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Biomedical subjects

A Crisanti

Publications and source records attributed to A Crisanti.

At least 37 records · Page 2Linked to original sources
PubMed1999

The A-domain and the thrombospondin-related motif of Plasmodium falciparum TRAP are implicated in the invasion process of mosquito salivary glands.

Sporozoites from all Plasmodium species analysed so far express the thrombospondin-related adhesive protein (TRAP), which contains two distinct adhesive domains. These domains share sequence and structural homology with von Willebrand factor type A-domain and the type I repeat of human thrombospondin (TSP). Increasing experimental evidence indicates that the adhesive domains bind to vertebrate host ligands and that TRAP is involved, through an as yet unknown mechanism, in the process of sporozoite motility and invasion of both mosquito salivary gland and host hepatocytes. We have generated transgenic P.berghei parasites in which the endogenous TRAP gene has been replaced by either P.falciparum TRAP (PfTRAP) or mutated versions of PfTRAP carrying amino acid substitutions or deletions in the adhesive domains. Plasmodium berghei sporozoites carrying the PfTRAP gene develop normally, are motile, invade mosquito salivary glands and infect the vertebrate host. A substitution in a conserved residue of the A-domain or a deletion in the TSP motif of PfTRAP impairs the sporozoites' ability to invade mosquito salivary glands. Notably, midgut sporozoites from these transgenic parasites are still able to infect mice. Midgut sporozoites carrying a mutation in the A-domain of PfTRAP are motile, while no gliding motility could be detected in sporozoites with a TSP motif deletion.

Animals↗
PubMed1999

Chromosome mapping in Cryptosporidium parvum and establishment of a long-range restriction map for chromosome VI.

We used contour-clamped homogeneous electric field (CHEF) gel electrophoresis and Southern blot hybridization to analyze the molecular karyotype of Cryptosporidium parvum and establish the chromosomal location of 12 single copy genes. In agreement with previous studies, the molecular karyotype of C. parvum was found to consist of partially co-migrating chromosomes ranging in size from 0.97 to 1.55 Mb and segregating into five distinct electrophoretic bands. Hybridization results allowed the definition of a linkage group comprised of five distinct loci located on chromosome VI. Southern hybridization and restriction analysis of total C. parvum chromosomes or isolated chromosome VI using gene-specific probes and an oligonucleotide specific for C. parvum telomeres allowed the development of a long-range restriction map of chromosome VI.

Animals↗
PubMed1999

Identification of heparin as a ligand for the A-domain of Plasmodium falciparum thrombospondin-related adhesion protein.

Thrombospondin-related adhesion protein (TRAP) is a Plasmodium falciparum transmembrane protein that is expressed within the micronemes of sporozoites, and is implicated in host cell invasion and motility. Contained within the extracellular region of TRAP is an A-domain, a module found in a number of membrane, plasma and matrix proteins, that is often involved in ligand recognition. In order to determine the role of the TRAP A-domain, it has been expressed as a glutathione S-transferase fusion protein and its ligand binding compared with that of other characterised glutathione S-transferase A-domain fusion proteins. Using a solid phase assay to screen for binding to known A-domain ligands, the TRAP A-domain was found to bind heparin. Binding to heparin appeared to be specific as it was saturable, and was inhibited by soluble heparin, fucoidan and dextran sulfate, but not by other negatively charged sulfated glycosaminoglycans such as chondroitin sulfates. Furthermore, unlike some A-domain ligand interactions, the A-domain of both TRAP and the leukocyte integrin, Mac-1, bound to heparin in the absence of divalent cations. It has been shown previously that another domain within TRAP, which is homologous to region II-plus of circumsporozoite protein, binds to sulfatide and to heparan sulfate on the immortalised hepatocyte line HepG2. The TRAP A-domain also bound to sulfatide and to HepG2 cells. Thus the A-domain shares certain binding properties already attributed to the region II-plus-like domain of TRAP, and may contribute to the binding of TRAP to heparan sulfate on hepatocytes.

Animals↗
PubMed1999

Pair dispersion in synthetic fully developed turbulence.

The Lagrangian statistics of relative dispersion in fully developed turbulence is numerically investigated. A scaling range spanning many decades is achieved by generating a two-dimensional velocity field by means of a stochastic process with prescribed statistics and of a dynamical model (shell model) with fluctuating characteristic times. When the velocity field obeys Kolmogorov similarity, the Lagrangian statistics is self similar and agrees with Richardson's predictions [Proc. R. Soc. London Ser. A 110, 709 (1926)]. For intermittent velocity fields the scaling laws for the Lagrangian statistics are found to depend on the Eulerian intermittency in agreement with the multifractal description. As a consequence of the Kolmogorov law the Richardson law for the variance of pair separation is, however, not affected by intermittency corrections. Moreover, Lagrangian exponents do not depend on the particular Eulerian dynamics. A method of data analysis, based on fixed scale statistics rather than usual fixed time statistics, is shown to give much wider scaling range, and should be preferred for the analysis of experimental data.

Journal Article↗
PubMed1999

Transformed Toxoplasma gondii tachyzoites expressing the circumsporozoite protein of Plasmodium knowlesi elicit a specific immune response in rhesus monkeys.

Toxoplasma gondii tachyzoites were transformed with the coding sequence of the circumsporozoite (CS) protein of the primate malaria parasite Plasmodium knowlesi. A single inoculation of live transformed tachyzoites elicited an antibody response directed against the immunodominant repeat epitope (EQPAAGAGG)2 of the P. knowlesi CS protein in rhesus monkeys. Notably, these animals failed to show a positive serum conversion against T. gondii. Antibodies against Toxoplasma antigens were detected only after a second inoculation with a higher number of transformed tachyzoites. This boost induced an increased antibody response against the P. knowlesi CS protein associated with immunoglobulin class switching, thus demonstrating the establishment of immunological memory. These results indicate that the Toxoplasma-derived CS protein is efficiently recognized by the monkey immune system and represents an immunodominant antigen in transformed parasites.

Amino Acid Sequence↗
PubMed1999

Thrombospondin related adhesive protein (TRAP), a potential malaria vaccine candidate.

We have investigated whether naturally induced immunity to Plasmodium falciparum thrombospondin related adhesive protein contributes to protection against malaria in humans. We have carried out a case control study in children living in an endemic region of West Africa to reveal associations between PfTRAP seroprevalence and the risk of cerebral malaria. Sera collected from the case and control groups were analysed by ELISA to compare their serum reactivity against PfTRAP, the circumsporozoite protein and the merozoite surface protein 1. Children with uncomplicated malaria had a significantly higher PfTRAP seroprevalence when compared to children with cerebral malaria. The risk of developing cerebral malaria appeared to depend on the reciprocal relationship between sporozoite inoculation rates and humoral immunity against PfTRAP. Our results suggest that naturally induced humoral immunity against PfTRAP contributes to the development of protection against severe malaria. Experimentally induced immunity against TRAP in different rodent models has consistently proven to elicit a high degree of protection against malaria. This together with the functional properties of TRAP and data describing CD4 and CD8 epitopes for PfTRAP indicate that this molecule could increase the protective efficiency of available sporozoite malaria vaccines.

Africa, Western↗
PubMed1998

Molecular cloning and expression analysis of a Cryptosporidium parvum gene encoding a new member of the thrombospondin family.

The apicomplexan parasite Cryptosporidium parvum invades and multiplies primarily in the brush border cells of the intestinal mucosa causing in AIDS patients a severe diarrhoea that represents a significant contributing factor leading to death. Morphological analysis indicates that the invasion machinery of C. parvum is similar to the apical complex of other parasites of the phylum Apicomplexa. We provide here evidence indicating that C. parvum also shares with these parasites a molecule crucial for the invasion of host cells. We have cloned a 3894 bp-long C. parvum cDNA encoding a protein characterised by sequence and structural similarities with members of the thrombospondin (TSP) family previously described in apicomplexan parasites of the genera Toxoplasma, Eimeria and Plasmodium. This novel C. partum molecule, the TSP-related adhesive protein of Cryptosporidium-1 (TRAP-C1), is encoded by a single copy gene containing no introns. TRAP-C1 is localised in the apical end of C. parvum sporozoites and is structurally related to the micronemal proteins MIC2 of Toxoplasma and Etp100 of Eimeria, which are involved in host-cell attachment and/or invasion. The identification of TRAP-C1 sheds new light on the molecules possibly involved in the invasion process of intestinal cells by C. parvum. We have also analysed the sequence variation of TRAP-C1 among C. parvum isolates and in the closely related species C. wrairi.

Amino Acid Sequence↗
PubMed1998

Understanding causal paths between mental illness and violence.

The stigma associated with mental illness is a major concern for patients, families, and providers of health services. One reason for the stigmatization of the mentally ill is the public perception that they are violent and dangerous. Although, traditionally, mental health advocates have argued against this public belief, a recent body of research evidence suggests that patients who suffer from serious mental conditions are more prone to violent behaviour than persons who are not mentally ill. It is a point of contention, however, whether the relationship between mental illness and violence is only one of association, or one of causality; that mental illness causes violence. A proven causal association between mental illness and violence will have major consequences for the mentally ill and major implications for caregivers, communities, and legislators. This paper outlines the key methodological barriers precluding casual inferences at this time. The authors suggest that a casual inference about mental illness and violence may yet be hasty. Because a premature statement advocating a causal relationship between mental illness and violence could increase stigma and have devastating effects on the mentally ill the authors urge researchers to consider the damage that may be produced as a result of poorly substantiated causal inferences.

Causality↗
PubMed1998

The Thrombospondin-related Protein Family of Apicomplexan Parasites: The Gears of the Cell Invasion Machinery.

A number of severe diseases of medical and veterinary importance are caused by parasites of the phylum Apicomplexa. These parasites invade host cells using similar subcellular structures, organelles and molecular species. Proteins containing one or more copies of the type I repeat of human platelet thrombospondin (TSP1), are crucial components of both locomotion and invasion machinery. Members of this family have been identified in Eimeria tenella, E. maxima, Toxoplasma gondii, Cryptosporidium parvum and in all Plasmodium species so far analysed. Here, Andrea Crisanti and colleagues discuss the structure, localization and current understanding of the function of TSP family members in the invasion of target cells by apicomplexan parasites.

Journal Article↗
PubMed1998

Multilocus genotypic analysis of Cryptosporidium parvum isolates from different hosts and geographical origins.

The genetic analysis of oocysts recovered from the stools of humans and animals infected with Cryptosporidium parvum has consistently shown the existence of two distinct genotypes. One of the genotypes is found exclusively in some human infections, whereas the other genotype is found in human as well as in animal infections. On the basis of these observations and the results of published epidemiological studies with single polymorphic markers, the existence of two separate transmission cycles has been postulated, one exclusively anthroponotic and the other involving both animals and humans. To test this hypothesis, C. parvum isolates of different geographic and host origins were analyzed by using unlinked genetic polymorphisms. A total of 28 isolates originating from Europe, North and South America, and Australia were examined. Isolates clustered into two groups, one comprising both human and animal isolates and the other comprising isolates only of human origin. The absence of recombinant genotypes is consistent with two reproductively isolated populations within the species C. parvum.

Animals↗
PubMed1998

Natural polymorphism in the thrombospondin-related adhesive protein of Plasmodium falciparum.

We have developed a typing system using natural sequence variation in the thrombospondin-related adhesive protein (TRAP) gene of Plasmodium falciparum. This method permits a haplotype to be assigned to any particular TRAP gene. We have applied this method to a hospital-based, case control-study in Mali. Previous sequence variation and conservation in TRAP has been confirmed. Particular TRAP haplotypes can be used as geographic hallmarks. Because of the high level of conflict between characters, we have examined the phylogenetic relationships between parasites using a network approach. Having received patient samples from urban and periurban areas of Bamako, the majority of haplotypes were closely related and distinct from TRAP sequences present in other continents. This suggests that the structure of TRAP can only tolerate a limited number of sequence variations to preserve its function but that this is sufficient to allow the parasite to evade the host's immune system until a long-lived immune response can be maintained. It may also reflect host genetics in that certain variants may escape the host immune response more efficiently than others. For vaccine design, sequences from the major regional variants may need to be considered in the production of effective subunit vaccines.

Animals↗
PubMed1997

TRAP is necessary for gliding motility and infectivity of plasmodium sporozoites.

Many protozoans of the phylum Apicomplexa are invasive parasites that exhibit a substrate-dependent gliding motility. Plasmodium (malaria) sporozoites, the stage of the parasite that invades the salivary glands of the mosquito vector and the liver of the vertebrate host, express a surface protein called thrombospondin-related anonymous protein (TRAP) that has homologs in other Apicomplexa. By gene targeting in a rodent Plasmodium, we demonstrate that TRAP is critical for sporozoite infection of the mosquito salivary glands and the rat liver, and is essential for sporozoite gliding motility in vitro. This suggests that in Plasmodium sporozoites, and likely in other Apicomplexa, gliding locomotion and cell invasion have a common molecular basis.

Animals↗
PubMed1997

PCR-RFLP analysis of the Cryptosporidium oocyst wall protein (COWP) gene discriminates between C. wrairi and C. parvum, and between C. parvum isolates of human and animal origin.

Cryptosporidium wrairi was isolated from guinea pigs during a spontaneous outbreak of cryptosporidiosis. Despite the morphological and antigenic similarities to C. parvum, C. wrairi displayed a different host range and site of infection and may represent a separate species or sub-species. We used the polymerase chain reaction to clone two distinct 550 bp-long DNA fragments, Wc-I and Wc-II, of the gene encoding the Cryptosporidium oocyst wall protein (COWP) of C. wrairi, which showed 98% identity to the C. parvum homologue. Within Wc-I, polymorphic Rsal restriction sites were used to develop a polymerase chain reaction-restriction fragment length polymorphism method able to distinguish C. wrairi from C. parvum and to identify two groups of C. parvum isolates differentially associated with animal and human infections.

Amino Acid Sequence↗
PubMed1997

Cloning and expression of the thrombospondin related adhesive protein gene of Plasmodium berghei.

Sporozoite recognition of host cells is a key step in the life-cycle of malaria parasites. Two sporozoite proteins have so far been characterized in some detail, the circumsporozoite protein (CS) and thrombospondin related adhesive protein (TRAP). We report here the cloning and expression of the TRAP gene homologue from Plasmodium berghei, PbTRAP. The PbTRAP gene encodes a protein of 606 amino acids having a deduced molecular mass of 66 kDa. The overall structure is clearly that of the TRAP family having a signal sequence followed by an integrin A domain, a sulphatide binding motif, followed by a proline based repeat before a transmembrane domain and helical cytoplasmic tail. The observed molecular mass is almost 50% larger than expected, this can be explained almost entirely by the abnormal behaviour in SDS-PAGE of the proline based repeat. As would be expected PbTRAP shows greatest similarity with the P. yoelli TRAP homologue sporozoite surface protein 2 (SSP2) than with PfTRAP, the TRAP gene from P. falciparum. The pattern of expression is similar to that of SSP2.

Amino Acid Sequence↗
PubMed1997

Cloning of the entire COWP gene of Cryptosporidium parvum and ultrastructural localization of the protein during sexual parasite development.

Molecular cloning and immunoelectron microscopy have been used to clone the full-length gene encoding Cryptosporidium parvum oocyst wall protein (COWP) and to analyse at the ultrastructural level the expression and localization of COWP during development in the gut. COWP is 1622 amino acids long, has a typical leader peptide and consists of 2 amino acidic domains each containing distinct repeated elements possibly originating from a common ancestral precursor. Electron microscopy localized COWP in a large cytoplasmic inclusion and in the wall-forming bodies of early and late macrogametes, respectively. Ultrastructural analysis of double-walled sporulating and mature oocysts indicated that COWP is selectively localized in the inner layer of the oocyst wall. This study provides the first localization at the ultrastructural level of a cloned coccidian oocyst wall protein.

Amino Acid Sequence↗