Immunoproteomic analysis of Plasmodium falciparum antigens using sera from patients with clinical history of imported malaria

BACKGROUND: The malaria caused by Plasmodium falciparum remains a serious public health problem in the world, due largely to the absence of an effective vaccine. There is a lack of information on the structural properties and antigens capable of activating the immunological mechanisms for the induction of protective immunity. Therefore, the objective of this study is to evaluate the serological reactivity of sera from individuals with imported malaria and identify major immunogenic proteins. METHODS: The study was conducted in 227 individuals with imported malaria and 23 healthy individuals who had never been in areas endemic for malaria. The determination of anti-P. falciparum IgG antibodies was performed by an ELISA validated and optimized for this study. Sera showing higher reactivity to anti-P. falciparum by ELISA were analysed by immunoblotting and immunogenic proteins were identified by mass spectroscopy. RESULTS: The results of anti-P. falciparum antibodies research by ELISA indicates 78 positive, 137 negative and 12 indeterminate sera. Analysis of immunoblotting demonstrated a consistent pattern with respect to immunoreactivity of antigens with molecular weights in the range of 40 to 60 kDa. Between 40 and 60 kDa six immunogenic proteins were identified: elongation factor-1 alpha (EF-1α), protein disulphide isomerase (PDI); phosphoglycerate kinase (PGK); 78 kDa glucose-regulated protein homologue (GRP-78); rhoptry-associated protein 2 (RAP-2) and rhoptry-associated protein 3 (RAP-3). CONCLUSIONS: It was identified immunogenic proteins essential for parasite survival in the host, two of which (RAP-2 and RAP-3) are already described in the literature as proteins that play an important role in the invasion of erythrocytes by extracellular merozoites.