The Plasmodium vivax Duffy Binding Protein (DBP) is the ligand in the major
pathway for P. vivax invasion of human reticulocytes, making it an appealing
vaccine candidate. Region II of DBP (DBP-RII) is the minimal portion of the
ligand that mediates recognition of the Duffy Antigen Receptor for Chemokines
(DARC receptor) on the reticulocyte surface and constitutes the primary vaccine
target. Analysis of natural variation in the coding sequences of DBP-RII revealed
signature evidence for selective pressure driving variation in the residues of the
putative receptor-binding site. We hypothesize that anti-DBP immunity in P. vivax
infections is strain-specific and hindered by polymorphic residues altering
sensitivity to immune antibody inhibition. To comprehend the human IgG
response following P. vivax infections we investigated the specificity of IgG in
Pursat Province, Western Cambodia. Using ELISAs, we quantified the antibody
titer against five variant alleles of DBP-RII. We also sequenced the DBP-RII of
the field isolates to determine their relationship to the variant alleles used in the
ELISAs. When correlating the IgG titer between the DBP variants a strainspecific
immune response was observed in patients with a high antibody titer to
DBP-RII_AH as compared to the other variants. This was different from the
correlation of high antibody titers between DBP-RII_P and DBP-RII_7.18
(?=0.88, p-value<0.0001) and DBP-RII_P and DBP-RII_O (?=0.87, p-
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value<0.0001). There appeared to be little correlation between specific
polymorphic residues and IgG titer. Understanding the immune response to the
polymorphisms within PvDBP will allow further identification of epitopes to enable
the production of a more effective P. vivax vaccine.