The characterization of naturally acquired anti-DBPII response is strain specific

The characterization of naturally acquired anti-DBPII response is strain specific. and H3 protective epitopes change sensitivity of immune inhibition by alteration of neutralizing antibody recognition. The present study indicates Thai variant H1.T1 (R308S), H3.T1 (D384G) and H3.T3 (K386N) are the most important variants for a DBPII candidate vaccine needed to protect in Thai residents. Introduction is usually a cause of morbidity and mortality in Thailand and other countries in South East Asia and worldwide about three billion people live at risk of infection by now accounts for more than 50% of all malaria cases since 2000 [3], [4]. Approximately 50% of the cases are in the migrant population. Vivax malaria is usually widespread and still an important problem in Thai-Cambodia border and Southern parts of Thailand in the Malayan peninsula. It is important to note that a significant portion of malaria cases in Thailand occur among temporary migrant workers from bordering countries [5], which presents a major challenge to prevention and control of malaria in the resident Pyrazinamide population. blood stages are responsible for clinical manifestation during contamination. In the blood stage preferentially invades reticulocytes expressing the Duffy Antigen Receptor for Chemokines (DARC) [6]. Parasite ligands, Reticulocyte binding proteins (RBPs) and Duffy binding protein (DBP), respectively, mediate these critical invasion preferences for merozoites, and is associated with the decisive junction formation step during the invasion process [8]. It is this critical conversation of DBP with its cognate receptor DARC that makes DBP an important anti-vivax vaccine candidate. The erythrocyte binding motif of DBP is in a 330-amino-acid cysteine rich domain name, referred to as Pyrazinamide DBP region II (DBPII) or the DBL domain name, and is the minimal domain name responsible for binding to DARC on Duffy-positive human erythrocytes [10], [11]. DBPII is an important vaccine candidate since anti-DBPII antibody inhibits binding to DARC, reduces merozoite invasion of human erythrocyte and can confer protection against blood stage contamination [12], [13], [14], [15]. However, the analysis alleles in field parasites showed that DBPII is usually hypervariable compared to other DBP regions. The SMOH polymorphisms occur frequently at certain residues in a pattern consistent with selection pressure on DBP, suggesting that allelic variation functions as a mechanism for immune evasion altering immune recognition of DBP and therefore might limit vaccine efficacy [16], [17], [18]. Understanding protective immunity against DBPII haplotypes common in vivax endemic area is necessary for finding strategy for vaccine design. In Thailand, a previous study found a high rate of nonsynonymous polymorphism of alleles among 30 Thai isolates. The highest frequency of polymorphism was found in residues D384G, R390H, L424I, W437R and I503K [19]. The phylogenetic analysis of Thai isolates exhibited that most Thai isolates shared distinct alleles with isolates from different geographical areas with some allele groups so far unique to Thailand [19]. Since DBPII polymorphisms among Thai isolates are extensive and some are unique, understanding naturally protective antibody against DBPII needs to be defined. In this study, we evaluated immune antibody activity directed against the most common Thai DBPII epitopes for their functional inhibition of DBPII. Results Naturally acquired responses to total (PvSE) and DBPII To assess the immunological responses during contamination, the reactivity of naturally acquired antibodies were tested against crude schizont antigen (PvSE) and the vaccine candidate DBPII. The anti-PvSE responses were very low in acutely infected patients (average OD?=?0.380.13), which had average antibody levels not significantly different from uninfected residents in the villages of the malaria endemic areas in Thailand (average OD?=?0.440.25) Pyrazinamide and na?ve controls (average OD?=?0.380.14)(Fig. 1A). In contrast the antibody titer specific to anti-DBPII responses in individual patient’s plasma samples were significantly elevated during infections (average OD?=?0.810.50) when compared with that of uninfected residents (average OD?=? 0.430.18) and na?ve controls (average OD?=?0.170.11)(Fig. 1B). In spite of this increased reactivity evident during vivax malaria infections, anti-DBPII responses of the Thai patients did not reveal any association between the parasitemia levels and the ages of patients (data not shown). The wide range of antibody responses to the recombinant.