Adaptation of in vitro cytoadherence assay to Plasmodium knowlesi field isolates

P. knowlesi was the first Plasmodium species in which antigenic variation was observed. Variation was due to schizont infected cell agglutination (SICAvar) antigens expressed by the parasite and transported to the exposed surface of the host erythrocyte [1]. PfEMP1 is P. falciparum’s orthologue of P. knowlesi’s SICA proteins [2]. In P. falciparum PfEMP1 is associated with infected erythrocytes binding to receptors such as ICAM-1 expressed on the endothelial cells of the host microvasculature. Here, we use a static protein assay [3] to determine if naturally occurring human P. knowlesi infections can cause erythrocytes to bind to ICAM-1, VCAM-1 and CD36

Characterization and tissue-specific expression patterns of the <it>Plasmodium chabaudi cir </it>multigene family

<p>Abstract</p> <p>Background</p> <p>Variant antigens expressed on the surface of parasitized red blood cells (pRBCs) are important virulence factors of malaria parasites. Whereas <it>Plasmodium falciparum </it>erythrocyte membrane proteins 1 (PfEMP1) are responsible for sequestration of mature parasites, little is known about putative ligands mediating cytoadherence to host receptors in other <it>Plasmodium </it>species. Candidates include members of the <it>pir </it>superfamily found in the human parasite <it>Plasmodium vivax </it>(<it>vir</it>), in the simian pathogen <it>Plasmodium knowlesi </it>(<it>kir</it>) and in the rodent malarias <it>Plasmodium yoelii </it>(<it>yir</it>), <it>Plasmodium berghei </it>(<it>bir</it>) and <it>Plasmodium chabaudi </it>(<it>cir</it>). The aim of this study was to reveal a potential involvement of <it>cir </it>genes in <it>P. chabaudi </it>sequestration.</p> <p>Methods</p> <p>Subfamilies of <it>cir </it>genes were identified by bioinformatic analyses of annotated sequence data in the <it>Plasmodium </it>Genome Database. In order to examine tissue-specific differences in the expression of cir mRNAs, RT-PCR with subfamily-specific primers was used. In total, 432 cDNA clones derived from six different tissues were sequenced to characterize the transcribed <it>cir </it>gene repertoire. To confirm differences in transcription profiles of <it>cir </it>genes, restriction fragment length polymorphism (RFLP) analyses were performed to compare different host tissues and to identify changes during the course of <it>P. chabaudi </it>infections in immunocompetent mice.</p> <p>Results</p> <p>The phylogenetic analysis of annotated <it>P. chabaudi </it>putative CIR proteins identified two major subfamilies. Comparison of transcribed <it>cir </it>genes from six different tissues revealed significant differences in the frequency clones belonging to individual <it>cir </it>gene subgroups were obtained from different tissues. Further hints of difference in the transcription of <it>cir </it>genes in individual tissues were obtained by RFLP. Whereas only minimal changes in the transcription pattern of <it>cir </it>genes could be detected during the developmental cycle of the parasites, switching to expression of other <it>cir </it>genes during the course of an infection was observed around or after peak parasitemia.</p> <p>Conclusions</p> <p>The tissue-specific expression of cir mRNAs found in this study indicates correlation between expression of CIR antigens and distribution of parasites in inner organs. Together with comparable results for other members of the <it>pir </it>superfamily this suggests a role of <it>cir </it>and other <it>pir </it>genes in antigenic variation and sequestration of malaria parasites.</p