Abstract
BackgroundPlasmodium vivax proteins with variant interspersed repeats (VIR) are the key proteins used by the parasite to escape from the host immune system through the creation of antigenic variations. However, few studies have been done to elucidate their role as targets of immunity. Thus, this study evaluated the naturally-acquired immune response against VIR proteins in vivax malaria-infected individuals in the Republic of Korea (ROK).MethodsSeven recombinant VIR proteins and two synthetic peptides previously studied in other countries that elicited a robust immune response were used to investigate the antibody and cellular immune response in 681 P. vivax-infected people in ROK. The expression of IgM, IgG, and IgG subclasses against each VIR antigen or against PvMSP1-19 was analysed by ELISA. PvMSP1-19, known as a promising vaccine candidate of P. vivax, was used as the positive control for immune response assessment. Furthermore, the cellular immune response to VIR antigens was evaluated by in vitro proliferative assay, cellular activation assay, and cytokine detection in mononuclear cells of the P. vivax-infected population.ResultsIgM or IgG were detected in 52.4% of the population. Among all the VIR antigens, VIR25 elicited the highest humoral immune response in the whole population with IgG and IgM prevalence of 27.8% and 29.2%, respectively, while PvMSP1-19 elicited even higher prevalence (92%) of IgG in the population. As for the cellular immune response, VIR-C2, PvLP2, and PvMSP1-19 induced high cell activation and secretion of IL-2, IL-6, IL-10, and G-CSF in mononuclear cells from the P. vivax-infected population, comparable with results from PvMSP1-19. However, no significant proliferation response to these antigens was observed between the malaria-infected and healthy groups.ConclusionModerate natural acquisition of antibody and cellular responses in P. vivax-infected Korean malaria patients presented here are similar to that in other countries. It is interesting that the immune response to VIR antigens is conserved among malaria parasites in different countries, considering that VIR genes are highly polymorphic. This thus warrants further studies to elucidate molecular mechanisms by which human elicit immune response to the malaria parasite VIR antigens.
Highlights
Plasmodium vivax proteins with variant interspersed repeats (VIR) are the key proteins used by the parasite to escape from the host immune system through the creation of antigenic variations
It is interesting that the immune response to VIR anti‐ gens is conserved among malaria parasites in different countries, considering that VIR genes are highly polymorphic
Antibody responses to VIR proteins and synthetic peptides Serum samples collected from 681 individuals living in the northern parts of Republic of Korea (ROK) and infected by P. vivax were tested by ELISA for the presence of IgM, IgG, and IgG subclasses antibodies
Summary
Plasmodium vivax proteins with variant interspersed repeats (VIR) are the key proteins used by the parasite to escape from the host immune system through the creation of antigenic variations. This study evaluated the naturally-acquired immune response against VIR proteins in vivax malaria-infected individuals in the Republic of Korea (ROK). Plasmodium vivax malaria remains an important problem in central and southeast Asia and South America, with more than 2 billion people at risk of infection [1, 2]. The area had been declared malaria-free by ROK and the World Health Organization in the 1970s, but malaria cases re-emerged in the 1990s [3]. An effective malaria vaccine capable of inducing a robust and long-lasting protection in naturally exposed individuals should be sought after. Studies evaluating immune responses against different P. vivax antigens will aid in the process of vaccine development
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