Homology blocks of Plasmodium falciparum var genes and clinically distinct forms of severe malaria in a local population

BMC Microbiology

Research Article

Edward B Baskerville¹  Mary M Rorick²  Mercedes Pascual³  Thomas S Rask⁴  Karen P Day⁴ 

[1] Department of Ecology and Evolutionary Biology, University of Michigan, 2019 Kraus Nat. Sci. Bldg., 830 North University Ave, 48109-1048, Ann ArborMichigan, USA;Department of Ecology and Evolutionary Biology, University of Michigan, 2019 Kraus Nat. Sci. Bldg., 830 North University Ave, 48109-1048, Ann ArborMichigan, USA;Howard Hughes Medical Institute, Ann Arbor, Michigan, USA;Department of Ecology and Evolutionary Biology, University of Michigan, 2019 Kraus Nat. Sci. Bldg., 830 North University Ave, 48109-1048, Ann ArborMichigan, USA;Howard Hughes Medical Institute, Ann Arbor, Michigan, USA;Center for Computational Medicine and Bioinformatics, University of Michigan, Ann Arbor, Michigan, USA;Department of Microbiology, Division of Medical Parasitology, New York University School of Medicine, New York City, New York, USA;

关键词: Plasmodium falciparum;    Malaria;    PfEMP1;    Var;    Severe disease;    Homology block;    Rosetting;    Impaired consciousness;    Recombination;    Balancing selection;   

DOI  :  10.1186/1471-2180-13-244

 received in 2013-07-18, accepted in 2013-10-26,  发布年份 2013

来源: Springer

【 摘 要 】

BackgroundThe primary target of the human immune response to the malaria parasite Plasmodium falciparum, P. falciparum erythrocyte membrane protein 1 (PfEMP1), is encoded by the members of the hyper-diverse var gene family. The parasite exhibits antigenic variation via mutually exclusive expression (switching) of the ~60 var genes within its genome. It is thought that different variants exhibit different host endothelial binding preferences that in turn result in different manifestations of disease.ResultsVar sequences comprise ancient sequence fragments, termed homology blocks (HBs), that recombine at exceedingly high rates. We use HBs to define distinct var types within a local population. We then reanalyze a dataset that contains clinical and var expression data to investigate whether the HBs allow for a description of sequence diversity corresponding to biological function, such that it improves our ability to predict disease phenotype from parasite genetics. We find that even a generic set of HBs, which are defined for a small number of non-local parasites: capture the majority of local sequence diversity; improve our ability to predict disease severity from parasite genetics; and reveal a previously hypothesized yet previously unobserved parasite genetic basis for two forms of severe disease. We find that the expression rates of some HBs correlate more strongly with severe disease phenotypes than the expression rates of classic var DBLα tag types, and principal components of HB expression rate profiles further improve genotype-phenotype models. More specifically, within the large Kenyan dataset that is the focus of this study, we observe that HB expression differs significantly for severe versus mild disease, and for rosetting versus impaired consciousness associated severe disease. The analysis of a second much smaller dataset from Mali suggests that these HB-phenotype associations are consistent across geographically distant populations, since we find evidence suggesting that the same HB-phenotype associations characterize this population as well.ConclusionsThe distinction between rosetting versus impaired consciousness associated var genes has not been described previously, and it could have important implications for monitoring, intervention and diagnosis. Moreover, our results have the potential to illuminate the molecular mechanisms underlying the complex spectrum of severe disease phenotypes associated with malaria—an important objective given that only about 1% of P. falciparum infections result in severe disease.

【 授权许可】

CC BY   
© Rorick et al.; licensee BioMed Central Ltd. 2013