Functional assays of Plasmodium vivax DBP, EBP, and RBP2b in erythrocyte invasion in Duffy-Negative Africans

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Project Summary Title: Plasmodium vivax Erythrocyte Invasion Mechanisms and Humoral Immune Response in Duffy Negative Africans Individuals of African ancestry are thought to be protected from Plasmodium vivax infection because they lack Duffy antigen expression on the surface of their erythrocytes rendering P. vivax unable to invade their red blood cells. However, an increasing number of P. vivax cases reported across Africa and in Duffy-negative individuals challenges this conventional dogma, raising the possibility that that some lineages of P. vivax may have evolved to use ligands other than Duffy Binding Protein for erythrocyte invasion. The intrinsic invasion mechanism and immune response of Duffy-negative individuals to P. vivax infections are largely unknown. In this application, we will investigate the expression and function of erythrocyte binding genes in Duffy-negative P. vivax and the antibody response of Duffy-negative individuals to P. vivax invasion proteins. There are three specific aims: 1) to identify genes with differential expression between Duffy-positive and Duffy-negative P. vivax by RNA-seq; 2) to determine in vitro binding and invasion activities of P. vivax ligand proteins identified from Aim 1 to Duffy- negative red blood cells; and 3) to examine in vivo antibody levels to targeted P. vivax antigens associated with erythrocyte invasion in Duffy-negative patients. As our study sites in Ethiopia have a large number of P. vivax cases and a significant proportion of Duffy-negative individuals, we have a unique opportunity to study the invasion mechanisms of P. vivax in Africa and fill critical knowledge gaps in how this phenomenon occurs. Our established lab culture facility close to the health centers and successful P. vivax transcriptome data obtained from cultured schizonts have demonstrated the feasibility of the proposed research. Comparison of P. vivax transcriptomes between Duffy-negative and Duffy-positive individuals will provide the first description of the genetic and functional attributes of P. vivax that permit infection of Duffy- negative erythrocytes. These data will be valuable to develop molecular markers that identify P. vivax strains able to infect Duffy-negative individuals. Such markers would enable wide-scale screening and characterization of this phenomenon and could radically change our understanding of P. vivax epidemiology in Africa. Further, the identification of key ligand protein(s) P. vivax uses for Duffy-negative erythrocyte invasion and host immune response will have important implications for P. vivax vaccine development.