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.

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.

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.

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.

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.

Antimalarial activity of synthetic analogues of distamycin

Malaria, one of the most serious diseases transmitted by arthropods, is largely present in tropical and even temperate zones in endemic or epidemic form. More than 40% of the world's population lives in areas at risk for exposure, and the World Health Organization reports that approximately 300 million people are affected by the infection (mostly caused by the species Plasmodium falciparum), with 1-2 million deaths per year. These data, and the fact that malaria is becoming increasingly refractory to treatment through resistance of the parasite to antimalarial agents currently in use, e.g., chloroquine, emphasize the need to develop new drugs. The well-known antiparasitic activity of oligopyrrolamidine natural products, such as distamycin and netropsin, suggested the antimalarial evaluation of related compounds obtained by new chemical modifications. Besides possessing antiviral and antitumoural properties, distamycin exhibits interesting in vitro activity against P. falciparum. Unfortunately, the high toxicity associated with this product precludes its development as a drug. However, some synthetic analogues of distamycin proved to be highly active against chloroquine-sensitive and -resistant strains of P. falciparum, besides showing low toxicity in vitro.

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.

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.

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.

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.

Conserved function of anopheles gambiae midgut-specific promoters in the fruitfly

Control of malaria by a methodology that would permit the effective blockage of the Anopheles gambiae midgut wall penetration by Plasmodium parasites requires a detailed understanding of both the physiology of the mosquito's digestion, and of the interactions between the parasite and its host. We have transformed Drosophila melanogaster with several constructs that allow the study of the promoter region of two of the major late trypsin genes of A. gambiae. Using several deletions, we have identified, for both genes, small genomic segments that are sufficient to confer tissue specificity to the promoter in a species that is far away in evolution from the mosquito. This will allow further studies that will enable both the understanding of the blood meal digestion, and may potentially be useful for the design of anti-plasmodial constructs at a later stage.

Constitutive and blood meal-induced trypsin genes in Anopheles gambiae

Trypsin genes in Anopheles gambiae are arranged as a tightly clustered gene family consisting of seven related coding sequences, devoid of introns. The two blood meal-inducible members of this family, Antryp1 and Antryp2, were shown to play a crucial role in the breakdown of the blood meal constituents. The role of Antryp3,4,5,6, and Antryp7 in the process of blood meal digestion remains to be elucidated. We have examined the localization and the expression patterns of these trypsins as well as the functional interactions in blood meal digestion between trypsins and other gut-specific proteases. Northern blot and RT-PCR analysis indicated that the genes Antryp3,4,5,6, and Antryp7 are all constitutively expressed in unfed female mosquitoes. Soon after blood feeding the mRNA of these trypsin genes became undetectable and appeared again at the end of the gonotrophic cycle. The blood meal-inducible trypsin Antryp1 was also constitutively expressed at low level in the gut of adult female mosquitoes. This trypsin was the only member of this gene family to be expressed in the gut of male and female pupae. By using antisera that specifically recognized recombinant Antryp4 we were able to show that the corresponding protein in Anopheles is synthesized and stored in the gut epithelium of unfed females as zymogen. Secretion and activation of this trypsin was shown to occur in the midgut lumen immediately after fluid ingestion and independently of the protein content of the meal. Recombinant trypsins expressed in Escherichia coli, with the exception of Antryp5 and Antryp6, were able to activate in vitro recombinant A. gambiae chymotrypsinogen, thus suggesting that blood meal ingestion is able to trigger a cascade of events leading to the activation of several proteases.

Molecular cloning and expression of a 70-kilodalton heat shock protein of Candida albicans

By screening an expression library of the yeast form of Candida albicans with a serum directed against whole fungal cells, a cDNA (2,325 bp) encoding a stress protein of C. albicans was cloned and sequenced. The cloned sequence (CaRLV130) identified a single open reading frame with a length of 1,968 bp coding for a protein containing 656 amino acid residues (70 kDa). The deduced amino acid sequence was 84% similar to the sequence of the Saccharomyces cerevisiae SSA1 gene, which encodes one member of the 70-kDa heat shock protein (Hsp70) family. The relevant gene (C. albicans HSP70 gene [CaHSP70]) was localized on the highest-M(r) (R1; approximately 3.8 Mb) chromosome of C. albicans as determined by pulse-field electrophoresis. CaHSP70 was expressed after heat shock, as demonstrated by Northern (RNA) blotting and reverse transcriptase-PCR with specific pairs of oligonucleotide sequences and gene probes. A recombinant protein was obtained in Escherichia coli after cloning of the full coding sequence into the BamHI site of the pDS56/RBSII6xhisE- plasmid and purification by nickel chelate affinity chromatography. The recombinant protein (6xhis-CaHsp70) was efficiently recognized in immunoblots by a monoclonal antibody directed against a common epitope of eukaryotic Hsp70 proteins, as well as by sera from normal human subjects. Moreover, immune mouse sera against the purified recombinant protein recognized native, heat-inducible constituents with sizes of around 70 kDa in whole-cell protein extracts of C. albicans. Overall, our data demonstrate that CaHSP70 encodes one member of a family of proteins (Hsp70) which usually represent highly conserved immunodominant antigens of infectious agents.

The effects of changes in the law concerning mentally disordered offenders: the Alberta experience with Bill C-30

OBJECTIVE

Until recently, the Criminal Code of Canada, enacted in 1892, stood stalwart to social, political and technological changes, particularly with respect to the regulations pertaining to the management of the mentally ill offender. This became more definitely so with the enactment of the Canadian Charter of Rights and Freedoms (1984) as many regulations in the Code about mentally ill offenders contravened the mandates contained in the Charter. The Supreme Court of Canada's decision on Regina v. Swain spurred the Federal Government to bring the regulations on the mentally ill offender into line with the Charter. The result was the enactment of Bill C-30 which was intended to dramatically change the way in which forensic psychiatry was practised in Canada. This paper presents the Alberta findings from a multi-site evaluation commissioned by the Federal Department of Justice to judge the effects of Bill C-30 on forensic health care practices.

METHODS

Health records data were used to compare utilization patterns from the year prior to the enactment of Bill C-30 with the year following. In addition, qualitative data were obtained from key clinical and legal informants outlining implementation difficulties that they had experienced.

RESULTS

Results support the judgement that Bill C-30 has not achieved its desired effects with respect to the length of the remand, and has resulted in an increased burden on hospitals and health care providers. In addition, an unanticipated finding was the increased use of the Mental Health Act which was considered to place forensic patients in a position of double jeopardy.

An evaluation of legal outcome following pretrial forensic assessment

This paper constitutes the first stage of data analysis in a larger controlled study designed to assess the effect of a forensic psychiatric assessment on legal disposition defined in three ways: 1. the number of days spent in custody prior to trial; 2. the number of sentenced days of incarceration; and 3. the conviction rate. A historical cohort design was used to follow two cohorts of individuals remanded, pretrial, to Southern Alberta Provincial Correctional Centres between 1988 and 1989. The study cohort consisted of all offenders detained who received a forensic psychiatric assessment. The comparison cohort consisted of a random sample of persons detained who did not undergo a forensic assessment. Because of small numbers, individuals below the age of 18 and women were excluded from study. This paper compares socio-legal characteristics of study and comparison subjects in order to better understand forensic psychiatric referral patterns and identify potentially confounding factors that would need to be controlled in subsequent analyses of legal outcomes. No differences were noted with respect to educational level but forensic subjects were found to be slightly older (average of 31 years compared to 29 years). Aboriginal peoples (Native Indian, Inuit and Metis) were three times more common among non-forensic offenders. Forensic patients were more likely to have had a prior forensic assessment but less likely to have a prior criminal detention. In addition, forensic patients were three times more likely to be charged with a crime against a person and counted more offenses in the target episode than comparison subjects.(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of the human antibody response to thrombospondin-related anonymous protein of Plasmodium falciparum

Thrombospondin-related anonymous protein (TRAP) of the malaria parasite Plasmodium falciparum shares two sequence motifs with other proteins which possess adhesive properties. Recently, findings indicate that TRAP is an antigen which contributes to antisporozoite immunity. We have cloned and expressed the TRAP coding sequences in Escherichia coli to investigate the human humoral immune response against this protein in a region of malaria endemicity of West Africa characterized by a seasonal transmission. Our results show that antibodies against TRAP are present in infected individuals. The anti-TRAP antibodies were analyzed in both a longitudinal and a prospective study. The longitudinal analysis shows seasonal fluctuations of the levels of specific antibodies as well as age-dependent quantitative differences. The immune response is long-lived in most of the adults and some of the older children but short-lived in young children. More importantly, the prospective analysis suggests that the presence of anti-TRAP antibodies in older children before the beginning of malaria transmission correlates with the subsequent control of parasite densities.

Thrombospondin related anonymous protein (TRAP) of Plasmodium falciparum in parasite-host cell interactions

Thrombospondin related anonymous protein (TRAP) of Plasmodium falciparum is characterized by the presence of an amino acid motif based on the sequence Trp-Ser-Pro-Cys-Ser-Val-Thr-Cys-Gly (WSPCSVTCG) that is found in a growing family of proteins. The sequence WSPCSVTCG is considered to confer sulpho-galactosyl-cerebroside (sulphatide) binding properties to antistasin, TSP, CS protein and properdin. The observation that TRAP is localized both on the micronemes and on the surface of P. falciparum sporozoites would suggest a role played by TRAP, and its putative sulphated glycoconjugates binding motif, in the recognition and/or entry of hepatocytes by the sporozoite. Our results indicated that TRAP constructs, expressed in E. coli, bind to sulpho-galactosyl-cerebrosides (sulphatides) and to the surface of HepG2 cells using the conserved amino acid motif WSPCSVTCG. Antisera raised against TRAP constructs inhibited sporozoite invasion of HepG2 cells thus suggesting, thus, that TRAP may be one of the parasite-encoded molecules implicated in the sporozoite invasion of hepatocytes. Moreover, the possibility that TRAP antibodies may be relevant in malaria immunity is supported by the results obtained in a prospective study conducted in a malaria endemic area. In adolescents, the presence of TRAP antibodies, before malaria transmission, correlated positively with the control of parasite density.

Temporal and spatial expression of serine protease genes in Anopheles gambiae

Serine proteases play a crucial role during the digestion of the blood meal in the mosquito gut. The isolation and the analysis of the genomic organisation of the corresponding genes may lead to the characterization of gut-specific, inducible promoters, suitable for the expression of anti-parasitic agents in the gut of transgenic mosquitoes. We report here on the identification of a trypsin and a chymotrypsin gene family of Anopheles gambiae. Following a blood meal, the transcription of all members of the two identified gene clusters, seven trypsin genes (Antryp1-7) and two chymotrypsin genes (Anchym1-2), is induced. Recombinant Antryp1 and Antryp2, expressed in E. coli, were both active in vitro against blood proteins. Moreover, mouse sera raised against Antryp1, Anchym1 and Anchym2 recognized the corresponding proteases among the proteins of a lysate prepared from dissected guts of An. gambiae mosquitoes.

Thrombospondin related anonymous protein (TRAP) of Plasmodium falciparum binds specifically to sulfated glycoconjugates and to HepG2 hepatoma cells suggesting a role for this molecule in sporozoite invasion of hepatocytes

Thrombospondin related anonymous protein (TRAP) of Plasmodium falciparum contains an amino acid motif based around the sequence WSPCSVTCG which is also found in region II of the circumsporozoite (CS) proteins of different species of Plasmodium. This amino acid motif confers on the CS protein the ability to bind specifically to sulfated glycoconjugates and to hepatocytes. This suggests that the interaction of CS protein with sulfated glycoconjugates on the surface of the hepatocytes may represent the first molecular event of sporozoite invasion of liver cells. Experimental evidence indicates that TRAP is localized both on the micronemes and on the surface of P. falciparum sporozoites implying that TRAP with its putative sulfated glycoconjugate binding motif may also be involved in recognition and/or entry of hepatocytes by the sporozoite. We show here that different TRAP constructs expressed in Escherichia coli bind to sulfogalactosyl-cerebrosides (sulfatides) and to the surface of HepG2 cells. These interactions are dependent on the presence of the conserved amino acid motif WSPCSVTCG within the sequences of the constructs and are completely inhibited by several sulfated glycoconjugates as well as by suramin, a polysulfonated drug with anti-protozoan activity. Moreover, sporozoite invasion of HepG2 cells is inhibited by antisera raised against these different TRAP constructs and by the presence of low concentrations of suramin. We concluded that TRAP may be one of the parasite encoded molecules in the host-parasite interaction that results in sporozoite invasion of hepatocytes.

Members of a trypsin gene family in Anopheles gambiae are induced in the gut by blood meal

Serine proteases are among the enzymes that play a crucial role during the digestion of the blood meal in the gut of mosquitoes. The identification of the corresponding genes would have important implications for the control of mosquitoes and mosquito-borne diseases. Analysis of the genomic organization of these genes may lead to the isolation of a gut-specific, inducible promoter for the expression of anti-parasitic agents in transgenic mosquitoes. Moreover, specific inhibitors could be designed on the basis of the structural properties of the enzymes. We report here on the identification of a trypsin gene family in Anopheles gambiae, the mosquito vector of malaria in Africa. Mosquito trypsin-related sequences were amplified by PCR using as template cDNA derived from RNA of blood fed mosquitoes. Cloning of the PCR product revealed two distinct sequences. Corresponding full-length cDNA clones were obtained and sequenced. Antryp1 and Antryp2 code for proteins of 274 and 277 amino acids respectively, showing 75% homology at the amino acid level. The deduced amino acid sequences clearly identify them as trypsins. Five additional trypsin sequences were found in overlapping genomic clones. The genes identified are tightly clustered within 11 kb and sequencing indicates that no introns are present. Northern and PCR analysis indicated that the transcription of both Antryp1 and Antryp2 is induced by blood feeding. Moreover, the Antryp1 protein was detected among the proteins of a midgut lysate of blood fed mosquitoes using antisera against recombinant Antryp1. In addition, the recombinant polypeptides derived from Antryp1 and Antryp2 expressed in Escherichia coli showed a strong proteolytic activity against different sets of blood proteins. We conclude that the products of Antryp1 and Antryp2 play an important role in the breakdown of the proteins during the digestion of the blood meal in the mosquito gut.

A method for collecting large quantities of Cryptosporidium parasites

The intestinal mucoso may be regarded as a potential and abundant source of Cryptosporidium parvurn parasites from which all developmental stages might be collected. If intracellular stages could be recovered from the brush border, many of the limitations concerned with the use of oocysts and in vitro cultures may be overcome. Hans-Michael Muller, Lorella Ranucci, Edoordo Pozio and Andrea Crisonti discuss here how this can be done.

Characterization and immunolocalization of a Cryptosporidium protein containing repeated amino acid motifs

The oocyst wall is one of the components that permits cryptosporidia both to survive in the environment and to retain infectivity. With the aim of identifying Cryptosporidium proteins specifically expressed at the oocyst stage, we screened lambda gt11 genomic libraries of Cryptosporidium parvum with both an oocyst antiserum and a specific genetic probe. We isolated, from distinct libraries, two overlapping clones containing an open reading frame encoding a 1,252-amino-acid polypeptide. The analysis of the deduced amino acid sequence revealed unusually high contents of cysteine, proline, and histidine. The sequence was also characterized by two distinct amino acid motifs, each repeated several times. The DNA sequences coding for the amino acid repeats showed a high frequency of synonymous mutations, a result suggesting that the repeated motifs may be functionally and/or structurally important to the parasite. Antisera and monoclonal antibodies developed against a recombinant polypeptide encompassing the first 786 amino acids revealed that the corresponding protein in C. parvum had an apparent molecular weight of 190,000. Moreover, confocal microscopy analysis with immunofluorescence indicated that the protein was localized on the oocyst wall as a uniform stain and within the oocyst itself as bright granules in close association with the residual body.

The human immune response against the major merozoite surface antigen of Plasmodium falciparum

The major surface antigen of the merozoite (MMSA) is very immunogenic in humans and it is considered a candidate for developing a malaria vaccine. This protein consists of conserved, dimorphic and polymorphic sequences that might differ in their ability to induce immunity. Epidemiological studies were undertaken in two different endemic areas of West Africa with the aim to identify the sequences within the protein that are the target of the humoral and cellular immune responses. Recombinant polypeptides expressed in E. coli, covering the conserved, the dimorphic and polymorphic regions, were used to evaluate the reactivity of sera and of Peripheral Blood Mononuclear Cells (PBMC) from inhabitants of rural communities exposed to P. falciparum transmission. The analysis of the humoral immune response against the MMSA showed that both qualitative and quantitative differences exist among groups of individuals with different susceptibility to P. falciparum infection. Furthermore, an association between intensity of transmission and antibody reactivity against the dimorphic regions was observed in individuals living in a malaria endemic area. The proliferative response of the PBMC was in most cases very low, however, several T cell clones could be established. The dimorphic region of MMSA was shown to contain T cell epitopes together with sequences most frequently recognized by human sera.

Human antibody response to the major merozoite surface antigen of Plasmodium falciparum is strain specific and short-lived

The precursor of the major merozoite antigen of Plasmodium falciparum, gp190, is considered a candidate for inclusion in a malaria vaccine. This protein, which consists of conserved, dimorphic, and polymorphic sequences, is very immunogenic in humans. In a longitudinal study carried out with 94 inhabitants of a rural community in Mali, West Africa, we show that in this endemic area naturally acquired gp190-specific antibodies are predominantly directed against the dimorphic parts of one of the main alleles of gp190. The presence of antibodies against these dimorphic regions correlates with the prevalence of the corresponding antigen in the infecting parasite population. Moreover, qualitative as well as quantitative differences were found in the time course of the humoral immune response to the dimorphic regions in adults and children, who differ in their susceptibility to malaria infection.

Polymorphism of the TRAP gene of Plasmodium falciparum

Natural sequence variation of the thrombospondin related anonymous protein (TRAP) gene of Plasmodium falciparum has been investigated by DNA analysis following the polymerase chain reaction amplification, and this shows the gene to be highly polymorphic. The region containing the sequence motif Trp-Ser-Pro-Cys-Ser-Val-Thr-Cys-Gly (WSPCSVTCG), common to TRAP, the circumsporozoite protein, properdin, and thrombospondin, was invariant. Elsewhere in the molecule, over 50 amino acid substitutions are described including the insertion of an in-frame, small-variable tandemly repeating motif between amino acid residues 352 and 353. Only one silent mutation was observed. Most nucleotide changes that occur in the first two codon positions result in conservative amino acid changes. Restriction fragment length polymorphism (RFLP) analysis was used to examine inheritance of TRAP in a cross between the HB3 and 3D7 clones of P. falciparum. Out of nine progeny examined, four possessed the HB3 gene and five the 3D7 gene. The TRAP gene hybridized to chromosome 13. Previous work has shown that a subtelomeric region of chromosome 13 from the 3D7 parent (marked by the HRP-III gene) was favoured strongly in this cross. The TRAP gene, however, is over 1 Mb away from this subtelomeric region and exhibits no such linkage because of chromosome crossovers. Five geographically separate isolates shared the same TRAP sequence as well as the same variant of the Th2R/Th3R region from the circumsporozoite protein. The correlation between independent markers in these isolates suggests that they have a common provenance.