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

Abstract

The development of modular constructs that include antigenic regions targeted by protective immune responses is an attractive approach for subunit vaccine development. However, a main concern of using these vaccine platforms is how to preserve the antigenic identity of conformational B cell epitopes. In the present study we evaluated naturally acquired antibody responses to a chimeric protein engineered to contain a previously defined immunodominant domain of the Plasmodium vivax reticulocyte binding protein-1 located between amino acid positions K435-I777. The construct also includes three regions of the cognate protein (F571-D587, I1745-S1786 and L2235-E2263) predicted to contain MHC class II promiscuous T cell epitopes. Plasma samples from 253 naturally exposed individuals were tested against this chimeric protein named PvRMC-RBP1 and a control protein that includes the native sequence PvRBP123-751 in comparative experiments to study the frequency of total IgG and IgG subclass reactivity. HLA-DRB1 and HLA-DQB1 allelic groups were typed by PCR-SSO to evaluate the association between major HLA class II alleles and antibody responses. We found IgG antibodies that recognized the chimeric PvRMC-RBP1 and the PvRBP123-751 in 47.1% and 60% of the studied population, respectively. Moreover, the reactivity index against both proteins were comparable and associated with time of exposure (p<0.0001) and number of previous malaria episodes (p<0.005). IgG subclass profile showed a predominance of cytophilic IgG1 over other subclasses against both proteins tested. Collectively these studies suggest that the chimeric PvRMC-RBP1 protein retained antigenic determinants in the PvRBP1435–777 native sequence. Although 52.9% of the population did not present detectable titers of antibodies to PvRMC-RBP1, genetic restriction to this chimeric protein does not seem to occur, since no association was observed between the HLA-DRB1* or HLA-DQB1* alleles and the antibody responses. This experimental evidence strongly suggests that the identity of the conformational B cell epitopes is preserved in the chimeric protein.

Induction of Multifunctional Broadly Reactive T Cell Responses by a Plasmodium vivax Circumsporozoite Protein Recombinant Chimera

“…A possible caveat when using chimeric recombinant proteins is the potential expression of neoantigens when the structure of the natural protein is modified. Naturally acquired antibodies in a population with differences in exposure and immunity (31) were able to recognize PvRMC-CSP when tested by ELISAs, confirming that the antigenic domains of CSP are conserved in our construct. The recognition of P. vivax sporozoites by mice immunized with PvRMC-CSP further confirms that antibody responses induced by this vaccine candidate are directed toward the P. vivax CSP native sequences.…”

“…To evaluate reactivity of naturally acquired antibodies against PvRMC-CSP, plasma samples were selected from 251 individuals from communities in Rondonia, a state in the western Amazon region of Brazil, where malaria is endemic. In the last 5 years, P. vivax malaria accounted for more than 70% of all malaria cases in the region as reported (30,31). The majority of the studied population consists of rainforest natives who have resided in the region where malaria is endemic for more than 25 years or transmigrants from several areas of Brazil where malaria is not endemic who have lived in Rondonia for 10 years or more.…”

“…The results for total IgG were expressed as reactivity indexes (RI) that were calculated by dividing the mean optical density of tested samples by the mean optical density plus 3 standard deviations of 5 nonexposed controls tested on each plate. Subjects were scored positive for serum IgG to a particular antigen if the RI was higher than 1 (30,31).…”

Major Histocompatibility Complex and Malaria: Focus on Plasmodium vivax Infection

“…However, other studies did not find associations between HLA-DR or HLA-DQ alleles and antibody response to P. vivax antigens. In a study performed by Ferreira and co-workers, no genetic restriction mediated by HLA-DRB1* and HLA-DQB1* against two constructions of P. vivax Reticulocyte Binding Protein-1 (PvRBP1) was verified in more than 500 HLA alleles from different individuals from communities in the Amazon region of Brazil ( 86 ). Moreover, regarding the cellular response, Arevalo-Herrera et al also did not observe association between HLA and cellular immune response of healthy volunteers vaccinated with CSP derived long synthetic peptides ( 96 ) and Lima-junior et al describe five promiscuous peptides from MSP-9 which also presented no association between HLA-DRB1 alleles and the cellular immune response ( 97 ).…”

The Presence, Persistence and Functional Properties of Plasmodium vivax Duffy Binding Protein II Antibodies Are Influenced by HLA Class II Allelic Variants

“…While malaria infection represents a key selection pressure for the human leukocyte antigen (HLA), and has left clear evolutionary footprints on the alleles observed in different countries [17], the association between HLA gene expression and responsiveness (or non-responsiveness) to defined malaria antigens has produced contradictory results [18–21]. Beyond the extreme genetic diversity of HLA class II, which hinders interpretation of the role of HLA on antibody responses elicited during malaria, most studies rely on antibody prevalence data collected at a single time-point in cross-sectional analysis of a population.…”