Antibody Responses and Avidity of Naturally Acquired Anti-Plasmodium vivax Duffy Binding Protein (PvDBP) Antibodies in Individuals from an Area with Unstable Malaria Transmission

Abstract

Plasmodium vivax remains an important cause of morbidity outside Africa, and no effective vaccine is available against this parasite. The P. vivax Duffy binding protein (PvDBP) is essential during merozoite invasion into erythrocytes, and it is a target for protective immunity against malaria. This investigation was designed to evaluate naturally acquired antibodies to two variant forms of PvDBP-II antigen (DBP-I and -VI) in malaria individuals (N = 85; median = 22 years) who were living in hypoendemic areas in Iran. The two PvDBP-II variants were expressed in Escherichia coli, and immunoglobulin G (IgG) isotype composition and avidity of naturally acquired antibodies to these antigens were measured using enzyme-linked immunosorbent assay (ELISA). Results showed that almost 32% of the studied individuals had positive antibody responses to the two PvDBP-II variants, and the prevalence of responders did not differ significantly (P > 0.05; χ2 test). The IgG-positive samples exhibited 37.03% and 40.8% high-avidity antibodies for PvDBP-I and PvDBP-VI variants, respectively. Furthermore, high-avidity IgG1 antibody was found in 39.1% of positive sera for each examined variant antigen. The avidity of antibodies for both PvDBP variant antigens and the prevalence of responders with high- and intermediate-avidity IgG, IgG1, and IgG3 antibodies were similar in patients (P > 0.05; χ2 test). Moreover, the prevalence of IgG antibody responses to the two variants significantly increased with exposure and host age. To sum up, the results provided additional data in our understanding of blood-stage immunity to PvDBP, supporting the rational development of an effective blood-stage vaccine based on this antigen.

Evaluation of Naturally Acquired IgG Antibodies to a Chimeric and Non-Chimeric Recombinant Species of Plasmodium vivax Reticulocyte Binding Protein-1: Lack of Association with HLA-DRB1*/DQB1* in Malaria Exposed Individuals from the Brazilian Amazon

“…However, the frequency of the natural antibody responses remained relatively low when compared to those against other classical P. vivax vaccine candidates, such as MSP-1 19 , MSP-9, MSP-3 and AMA-1, which have frequencies that ranged between 60% and 90% of reactivity against their most immunogenic regions [12], [15], [42]. On the other hand, the data is still comparable to proteins such as DBP [43] and the N-terminal region of MSP-9 [44].…”

Functional Antibodies against VAR2CSA in Nonpregnant Populations from Colombia Exposed to Plasmodium falciparum and Plasmodium vivax

“…The avidity index (AI) was calculated as the ratio of the OD value of urea-treated samples to that of the untreated samples, multiplied by 100. All AI values less than 30% were considered low-avidity antibodies, values between 30% and 50% were considered intermediate-avidity antibodies, and values greater than 50% were considered high-avidity antibodies (37).…”

Optimized Method for Purification of Expressed Plasmodium Vivax Duffy Binding Protein-II (PvDBP-II): Implication for Vivax Malaria Vaccine Development

“…The ELISA results showed that 42.1% of the patients were positive responder for rDBP-IX which was higher than a former study in Iran (32%) [27], however this result was comparable with those from unstable malaria transmission regions such as Colombia (40%) [28] and Brazilian Amazon region (50%) [19]. According to previous studies, the dominance of cytophilicIgG1 and IgG3 subclasses has been reported in response to malaria infection [27,29].…”

“…According to previous studies, the dominance of cytophilicIgG1 and IgG3 subclasses has been reported in response to malaria infection [27,29]. The suggested mechanism by which these subclasses are protective includes their binding to the Fc receptors on the monocytes, leading to antibody dependent cell mediated inhibition of the parasite replication.…”