Immunological characterization of antibodies and antigens of Plasmodium falciparum in plasma samples obtained from individuals who previously stayed in malaria-endemic areas

Introduction The development of protective immunity against Plasmodium spp. requires several exposures to the parasite. However, when the immune system is no longer stimulated by the contact with the parasite, the period of time in which the parasite antibodies persist in the bloodstream is not clear. Previous studies verified Plasmodium spp. antibodies in the bloodstream of individuals with their last exposure time 10 or more years before the studies execution. Thus, the principal aims of this work are to characterize the immunoglobulins regarding its subclasses and their persistence time in the bloodstream, and to identify parasitic proteins responsible for the serological reactivity, in individuals with previous stays in endemic areas of malaria.
Materials and Methods Individuals with previous stays in an endemic area of malaria were included in this study. Plasma samples were analysed by an ELISA technique to detect antibodies against Plasmodium sp. (Malaria EIA Test Kit Biorad-USA). Subsequently, the reactive samples were analysed regarding to the immunoglobulins subclasses with specificity for Plasmodium falciparum, through an ‘in house’ ELISA technique. The reactive samples were used to study the antigenic reactivity through Western Blot.
Results From 321 samples collected, 76 were serological reactive to total antibodies against Plasmodium spp., from which 11 were reactive to IgM and 51 to total IgG against P. falciparum. Those 51 samples were used to study the antigenic reactivity to P. falciparum: the proteins with more frequent reactivity had molecular weight between 40–50 and 80–120 kDa. From the 76 reactive samples to total antibodies against Plasmodium, 61.3% are individuals with their last return from an endemic area 6 months before the study execution, 6.7% return 6 months–1 year before the study, 6.7% 2–9 years and 25.3% 10 or more years before the study execution.
Conclusion Antibodies against Plasmodium spp. may remain detectable in the bloodstream several years after the return of the individual from an endemic area. Thus, it is essential identify the parasitic proteins responsible for the serological reactivity, to understand why those antibodies remain in the bloodstream so many years after the last exposure time, as well as the role of those parasitic proteins in the malaria immunity. This knowledge could be an important factor in the development of new markers for serological diagnosis or vaccines.
Disclosure Nothing to disclose.