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NICOLETE, V. C. Duffy blood group polymorphism and naturally acquired IgG antibodies to Plasmodium vivax Duffy binding protein (PvDBP) in rural Amazonians. 2012. 96 p. Masters thesis (Biology of the Relation Pathogen-Host) – Instituto de Ciências Biomédicas, Universidade de São Paulo, São Paulo, 2012. In Brazil 99, 9% of the reported cases of malaria originate from Amazon region and 90% of them are due to Plasmodium vivax. To invade their target cells, young erythrocytes knwon as reticulocytes, P. vivax merozoites recognize specific receptors on the host cell surface. One of the major parasites ligands is the Duffy binding protein (PvDBP), expressed in micronemes, which binds specifically to a erythrocyte membrane glycoprotein known as Duffy blood group antigen/receptor for chemokines (DARC). Interaction between cysteine-rich domain II of PvDBP and DARC is crucial for red blood cell invasion and DARC-negative individuals are usually resistant to blood-stage infection with P. vivax; therefore, PvDBP is a major vaccine candidate antigen. Here, we investigated IgG antibody responses to three recombinant proteins derived from PvDBP and MSP119 (19 kDa C-terminal region of the merozoite surface protein-1 of the P. vivax), in 343 subjects exposed to hypoendemic malaria in the Amazon Basin of Brazil. Both recombinant proteins Sal III-IV-GST and Sal III-His contain part (either domains II to IV or domain II alone) of the Sal I variant of PvDBP fused to either GST or a histidine tail, while OII-His contain the domain II of the PNG-O variant fused to a histidine tail; recombinant proteins Sal III-His and OII-His (but not Sal III-IV-GST) were refolded to reproduce the native conformation of PvDBP. IgG antibodies to Sal III-His, OIIHis, Sal III-IV-GST and MSP119-GST were found in 43,7 %, 39,0%, 14,3% and 38,8% of the subjects, with a strong positive correlation between antibody levels to the Sal III-His and OIIHis but a poor positive correlation between levels of antibodies to these refolded proteins and non-refolded Sal III-IV-GST (which shares the same domain II sequence with Sal III-His) and MSP119-GST. Current P. vivax infection (as detected by microscopy or PCR) and cumulative exposure to malaria (as determined by the lenght of residence in endemic areas) were significantly associated with increased antibody responses. The Duffy genotypes FY*AFY*B and FY*B ES FY*B ES [DARC negative] were the most and least common genotypes, respectively. As expected, FY*B ES FY*B ES individuals were less likely to have antibodies to PvDBP, but we found similar proportions of seropositive subjects with the FY*A*FY*A, FY*AFY*B ES , FY*B*FY*B and FY*BFY*B ES genotypes. Sequence analysis revealed several region II PvDBP variants in 41 local P. vivax isolates. The most common of them (found in 28,8% isolates) differs from Sal I and PNG-O alleles in six amino acid codons (including N417K change, which has previously been shown to be part of a linked haplotype that alters PvDBP sensitivity to inhibitory antibody). No Sal I-type variant, from which a PvDBP-based vaccine prototype currently under clinical testing has been derived, was found in local parasites.

Polimorfismo no grupo sanguíneo Duffy e anticorpos IgG naturalmente adquiridos contra a proteína de ligação em Duffy de Plasmodium vivax (PvDBP) na Amazônia rural brasileira.