Genetic diversity in two Plasmodium vivax protein ligands for reticulocyte invasion.

Camille Roesch,Didier Menard,Vorleak Run,David Serre,Chetan E Chitnis,Christèle Huon,Stéphanie Ramboarina,Jean Popovici,Emma Rakotomalala,Rado Lalaina Rakotoarison,Tsikiniaina Rasoloharimanana,Saorin Kim,Micheline Guillotte-Blisnick,Zo Andriamanantena,Sophalai Bin,Anuj Kumar,Inès Vigan-Womas,Rhoel Ramos Dinglasan

doi:10.1371/journal.pntd.0006555

Abstract

The interaction between Plasmodium vivax Duffy binding protein (PvDBP) and Duffy antigen receptor for chemokines (DARC) has been described as critical for the invasion of human reticulocytes, although increasing reports of P. vivax infections in Duffy-negative individuals questions its unique role. To investigate the genetic diversity of the two main protein ligands for reticulocyte invasion, PvDBP and P. vivax Erythrocyte Binding Protein (PvEBP), we analyzed 458 isolates collected in Cambodia and Madagascar from individuals genotyped as Duffy-positive. First, we observed a high proportion of isolates with multiple copies PvEBP from Madagascar (56%) where Duffy negative and positive individuals coexist compared to Cambodia (19%) where Duffy-negative population is virtually absent. Whether the gene amplification observed is responsible for alternate invasion pathways remains to be tested. Second, we found that the PvEBP gene was less diverse than PvDBP gene (12 vs. 33 alleles) but provided evidence for an excess of nonsynonymous mutations with the complete absence of synonymous mutations. This finding reveals that PvEBP is under strong diversifying selection, and confirms the importance of this protein ligand in the invasion process of the human reticulocytes and as a target of acquired immunity. These observations highlight how genomic changes in parasite ligands improve the fitness of P. vivax isolates in the face of immune pressure and receptor polymorphisms.

Highlights

Plasmodium vivax is a predominant cause of malaria outside Africa, which causes significant morbidity and places an enormous economic burden on many resource poor countries [1]
Seminal works with controlled experimental infections of volunteers through sporozoite challenge and in vitro invasion studies using P. knowlesi as a model subsequently established the paradigm that the Duffy antigen is required for reticulocyte invasion by P. vivax [9,10,11]
Plasmodium vivax Duffy binding protein (PvDBP) copy number variation (CNV) was assessed in 458 P. vivax isolates collected in Cambodia (N = 392) and Madagascar (N = 66) (Table 1)

Summary

Introduction

Plasmodium vivax is a predominant cause of malaria outside Africa, which causes significant morbidity (estimate of 8.5 million cases in 2016) and places an enormous economic burden on many resource poor countries [1]. Vivax malaria was considered a benign infection compared to P. falciparum, clinical episodes and regular recurrent infections cause significant morbidity [2]. Previous data from malaria therapy, which was used extensively for over two decades (1920–1940) for treatment of neurosyphilis (e.g. paralysis of the insane), as well as experimental infections of volunteers have demonstrated that individuals of African origin were naturally resistant to P. vivax infection [4,5,6]. Seminal works with controlled experimental infections of volunteers through sporozoite challenge and in vitro invasion studies using P. knowlesi as a model subsequently established the paradigm that the Duffy antigen is required for reticulocyte invasion by P. vivax [9,10,11]. Vivax malaria was long thought to be absent from parts of Africa where the Duffy-negative phenotype is highly frequent [12]

Methods

Results

Conclusion