Amplification of Duffy binding protein-encoding gene allows Plasmodium vivax to evade host anti-DBP humoral immunity

Abstract

Antigenic variation, the capacity to produce a range of variable antigens, is a well-described strategy of Plasmodium and other parasites to evade host immunity. Here, we show that gene amplification is an additional evasion mechanism used by Plasmodium vivax to escape humoral immunity targeting PvDBP, the key ligand involved in reticulocyte invasion. PvDBP gene amplification leads to increased mRNA levels and protects P. vivax in vitro against invasion inhibitory human monoclonal antibodies targeting a conserved binding domain of DBP. Patient samples suggest that parasites with increased pvdbp copy number are able to infect individuals with naturally acquired antibodies highly blocking the binding of PvDBP to the Duffy receptor. These results show that gene copy number variation affect the parasite's ability to evade anti-PvDBP humoral immunity.

The biology of unconventional invasion of Duffy-negative reticulocytes by Plasmodium vivax and its implication in malaria epidemiology and public health

“…Since most individuals of African origin are Duffy-negative and do not express the DARC antigen on the surface of their erythrocytes, it is unclear whether the high prevalence of Duffy-negative alleles in African populations results Fig. 1 Interaction between parasite ligands and reticulocyte receptors during invasion process of Duffy-positive and Duffy-negative cells by Plasmodium vivax (adapted from Popovici et al [50]). A spectrum of ligands on the merozoite surface of the parasites that may bind to Duffy-negative and Duffy-positive reticulocytes are presented from P. vivax resistance selection [76] or there exists hidden transmission of P. vivax among Duffy-negative populations.…”

“…Unfortunately, the inherent challenge of culturing P. vivax in vitro has made studies targeting vivax malaria very difficult [62]. The involvement of putative parasite ligands in the invasion of Duffy-negative individuals has been described in a number of studies, but it remains unclear what specific receptor on the human erythrocyte is aiding the entry of P. vivax in Duffy-negative reticulocytes [50].…”

“…It is as yet unclear whether a few Duffy molecules present on the surface of the erythrocyte enabling parasites with multiple PvDBP gene copies to invade the cell, or whether the invasion process of Duffy-negative reticulocytes could occur through alternate pathways by non-DBP ligands (PvEBP, PvMSP1P, or PvGAMA) [50]. Another plausible explanation for Duffy-negative invasion is that the Duffy-negative phenotype may not be entirely a Duffy null and that the Duffy receptor may be expressed at a subtle level sufficient enough for low level invasion.…”

“…Assuming a high adaptability of Plasmodium species, it is likely that the duplications emerged in the parasites in response to the variation in human Duffy blood group across malaria-endemic settings. Recent studies have shown that PvDBP gene amplification not only facilitates binding to an alternative lower affinity receptor in Duffy-negative reticulocytes [ 16 , 44 ], but also allows P. vivax to evade host anti-PvDBP humoral immunity [ 50 ], reassuring PvDBPII region as a promising candidate for a blood-stage vaccine against P. vivax [ 34 ]. The polymorphic nature of Pv DBP certainly allows P. vivax to colonize diverse ecological niches as well as to evade the host immune system.…”

“…The detection of P. vivax DNA by molecular and serological assays in a Duffy-negative individual’s blood sample could represent pre-erythrocytic stages of the parasites, independent of blood-stage infection [ 48 ]. Therefore, microscopic observation of P. vivax within Duffy-negative erythrocytes coupled by confirmation by genotyping has essentially proved Duffy-negative infection [ 50 ]. The first microscopic observation of P. vivax infection in a Duffy-negative erythrocyte was reported by Ryan et al, in Kenya in [ 39 ] followed by a definitive evidence of a P. vivax infection within Duffy-negative erythrocyte from patients in Madagascar [ 15 ].…”