Strain-specific protective effect of the immunity induced by live malarial sporozoites under chloroquine cover.

The efficacy of a whole-sporozoite malaria vaccine would partly be determined by the strain-specificity of the protective responses against malarial sporozoites and liver-stage parasites. Evidence from previous reports were inconsistent, where some studies have shown that the protective immunity induced by irradiated or live sporozoites in rodents or humans were cross-protective and in others strain-specific. In the present work, we have studied the strain-specificity of live sporozoite-induced immunity using two genetically and immunologically different strains of Plasmodium cynomolgi, Pc746 and PcCeylon, in toque monkeys.

A single parasite gene determines strain-specific protective immunity against malaria: the role of the merozoite surface protein I.

Despite many decades of research, no registered vaccine against the pathogenic blood stages of the malaria parasite exists, translating into the loss of many hundreds of thousands of young lives each year in tropical Africa. Although many parasite proteins have been shown to induce immune responses in the host, proof for their induction of protective immunity is still lacking. We previously reported a novel genetic approach called linkage group selection (LGS) for rapid identification of target antigens of strain-specific protective immunity (SSPI) against malaria.

Gene encoding erythrocyte binding ligand linked to blood stage multiplication rate phenotype in Plasmodium yoelii yoelii.

Variation in the multiplication rate of blood stage malaria parasites is often positively correlated with the severity of the disease they cause. The rodent malaria parasite Plasmodium yoelii yoelii has strains with marked differences in multiplication rate and pathogenicity in the blood. We have used genetic analysis by linkage group selection (LGS) to identify genes that determine differences in multiplication rate.

Strain-specific immunity may drive adaptive polymorphism in the merozoite surface protein 1 of the rodent malaria parasite Plasmodium chabaudi.

Clinical immunity against malaria is slow to develop, poorly understood and strongly strain-specific. Understanding how strain-specific immunity develops and identifying the parasite antigens involved is crucial to developing effective vaccines against the disease. In previous experiments we have shown that strain-specific protective immunity (SSPI) exists between genetically distinct strains (cloned lines) of the rodent malaria parasite Plasmodium chabaudi chabaudi in mice [Cheesman, S.

Congenicity and genetic polymorphism in cloned lines derived from a single isolate of a rodent malaria parasite.

Many of the most commonly studied lines of the rodent malaria parasite Plasmodium yoelii yoelii originated from a single parasite isolate designated 17X. Amongst these lines, however, are parasites that exhibit variation in genotype and phenotype (e.g.

Linkage group selection: towards identifying genes controlling strain specific protective immunity in malaria.

Protective immunity against blood infections of malaria is partly specific to the genotype, or strain, of the parasites. The target antigens of Strain Specific Protective Immunity are expected, therefore, to be antigenically and genetically distinct in different lines of parasite. Here we describe the use of a genetic approach, Linkage Group Selection, to locate the target(s) of Strain Specific Protective Immunity in the rodent malaria parasite Plasmodium chabaudi chabaudi.

Gene encoding a deubiquitinating enzyme is mutated in artesunate- and chloroquine-resistant rodent malaria parasites.

Artemisinin- and artesunate-resistant Plasmodium chabaudi mutants, AS-ART and AS-ATN, were previously selected from chloroquine-resistant clones AS-30CQ and AS-15CQ respectively. Now, a genetic cross between AS-ART and the artemisinin-sensitive clone AJ has been analysed by Linkage Group Selection. A genetic linkage group on chromosome 2 was selected under artemisinin treatment.

Linkage Group Selection--a fast approach to the genetic analysis of malaria parasites.

Genetic analysis of malaria parasites has shown that the mechanisms of inheritance in these organisms are classically Mendelian. In other words, alleles of genes at different loci recombine, and alleles at the same gene locus segregate, in the progeny of a genetic cross between two genetically distinct lines of malaria parasite. Importantly, such progeny are haploid in the first filial generation following genetic crossing.

Mixed strain infections and strain-specific protective immunity in the rodent malaria parasite Plasmodium chabaudi chabaudi in mice.

Important to malaria vaccine design is the phenomenon of "strain-specific" immunity. Using an accurate and sensitive assay of parasite genotype, real-time quantitative PCR, we have investigated protective immunity against mixed infections of genetically distinct cloned "strains" of the rodent malaria parasite Plasmodium chabaudi chabaudi in mice. Four strains of P.

Virulence and competitive ability in genetically diverse malaria infections.

Explaining parasite virulence is a great challenge for evolutionary biology. Intuitively, parasites that depend on their hosts for their survival should be benign to their hosts, yet many parasites cause harm. One explanation for this is that within-host competition favors virulence, with more virulent strains having a competitive advantage in genetically diverse infections.

A genetic approach to the de novo identification of targets of strain-specific immunity in malaria parasites.

Vaccine research in malaria has a high priority. However, identification of specific antigens as candidates for vaccines against asexual blood stages of malaria parasites has been based on largely circumstantial evidence. We describe here how genes encoding target antigens of strain-specific immunity in malaria can be directly located in the parasite's genome without prior information concerning their identity, by the method we call linkage group selection.

Amplified fragment length polymorphism measures proportions of malaria parasites carrying specific alleles in complex genetic mixtures.

We are interested in developing a method for the identification of those genes in malaria parasites which underlie a variety of selectable phenotypes of the parasites including drug resistance and strain-specific immunity. A key aspect of our approach is to subject a genetically mixed population of malaria parasites to a specific phenotypic selection pressure such as the administration of an antimalarial drug and then identify genetic markers affected by the selection. Our aim, therefore, is to be able to identify those genetic markers carried by sensitive parasites which disappear from the population after selection as they should be closely linked to the locus determining the phenotype involved.

Host heterogeneity is a determinant of competitive exclusion or coexistence in genetically diverse malaria infections.

During an infection, malaria parasites compete for limited amounts of food and enemy-free space. Competition affects parasite growth rate, transmission and virulence, and is thus important for parasite evolution. Much evolutionary theory assumes that virulent clones outgrow avirulent ones, favouring the evolution of higher virulence.

Real-time quantitative PCR for analysis of genetically mixed infections of malaria parasites: technique validation and applications.

A technique that can distinguish and quantify genetically different malaria parasite clones in a mixed infection reliably and with speed and accuracy would be very useful for researchers. Many current methods of genotyping and quantification fall down on a number of aspects relating to their ease of use, sensitivity, cost, reproducibility and, not least, accuracy. Here we report the development and validation of a method that offers several advantages in terms of cost, speed and accuracy over conventional PCR or antibody-based methods.