Abstract
BackgroundMalaria is a major global cause of deaths and a vaccine is urgently needed.ResultsWe have employed the P. falciparum merozoite antigens MSP2-3D7/FC27 and AMA1, used them in ELISA, and coupled them in different ways using surface plasmon resonance (SPR) and estimated affinity (measured as kd) of monoclonal as well as naturally-acquired polyclonal antibodies in human plasma. There were major differences in kd depending on how the antigens were immobilized and where the His-tag was placed. For AMA1 we could see correlations with invasion inhibition. Using different immobilizations of proteins in SPR, we could see only moderate correlations with levels of antibodies in ELISA, indicating that in ELISA the proteins were not uniformly bound and that antibodies with many specificities exist in natural immunisation. The correlations between ELISA and SPR were enhanced when only parasite positive samples were included, which may indicate that high affinity antibodies are difficult to maintain over long periods of time. We found higher kd values for MSP2 (indicating lower affinity) compared to AMA1, which might be partly explained by MSP2 being an intrinsically disordered protein, while AMA1 is globular.ConclusionsFor future vaccine studies and for understanding immunity, it is important to consider how to present proteins to the immune system to achieve highest antibody affinities.Electronic supplementary materialThe online version of this article (doi:10.1186/s12866-015-0461-1) contains supplementary material, which is available to authorized users.
Highlights
Malaria is a major global cause of deaths and a vaccine is urgently needed
Some of the antibodies are directed against merozoite antigens of the parasite, like Merozoite Surface Protein 2 (MSP2) and Apical Membrane Antigen 1 (AMA1) [5,6,7,8,9,10]
Affinity of human antibodies using N-or C-terminal amine coupling of antigens to the chip After observing variable affinity responses for antibodies against MSP2 and AMA1 proteins, we investigated whether the coupling chemistry and/or orientation of the proteins affected the kd values
Summary
Malaria is a major global cause of deaths and a vaccine is urgently needed. Some of the antibodies are directed against merozoite antigens of the parasite, like Merozoite Surface Protein 2 (MSP2) and Apical Membrane Antigen 1 (AMA1) [5,6,7,8,9,10]. The parasite antigen appears more ordered, which may be due to interactions with the merozoite membrane or oligomerization of MSP2 [16]. MSP2 parasite alleles can be categorized into two major groups, 3D7 and FC27 [6, 17]
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