Rosetting (binding of infected erythrocytes to uninfected ones) is a parasite adhesion phenotype thought to be mediated by Plasmodium falciparum membrane protein 1 (PfEMP1). Despite the association between rosetting and severe malaria in Africa, rosette-mediating PfEMP1 variants from African-derived strains are yet to be characterized.
I initially attempted to detect the predominantly expressed var genes in five recently culture-adapted Kenyan P. falciparum isolates selected for rosetting. Unfortunately no clear rosetting-associated genes could be detected, possibly because of incomplete selection and lack of a clear phenotype in the selected parasites.
I then went on to study another Kenyan parasite line, SA075, whose predominant var gene tag had interesting sequence features previously linked to rosetting. Using PCR walking, cloning and sequencing, I identified the full-length var gene corresponding to this tag, called SA075var1. Subsequent experiments failed to confirm a role for the PfEMP1 variant encoded by SA075var1 in rosetting. However, SA075var1 had domain cassette DC 8-like features which have lately been linked to severe disease.
Antibodies raised in rabbits against recombinant proteins from domains of SA075var1 revealed functional antibodies with an ability to recognize the surface of parasite infected erthrocytes and to mediate phagocytosis. Although mainly variant-specific, the antibodies showed limited cross-reactivity with one other parasite strain.
Using plasma pairs from Kenyan malaria patients, I examined antibody responses against SA075 and four other rosetting P. falciparum strains selected to enrich for single rosette-mediating variants. Antibody responses were seen against particular rosette-elected strains suggesting that some variants may be important for particular severe malaria syndromes.
Overall, the data described in this thesis demonstrates the need for continued research into functional and immunological characterization of PfEMP1 variants, especially in field isolates. Antibody data however showed clinical relevance of some rosette-mediating variants that could become important targets for malaria intervention studies
