Plasmodium vivax: comparison of immunogenicity among proteins expressed in the cell-free systems of Escherichia coli and wheat germ by suspension array assays

Five Plasmodium vivax antigens representing leading vaccine candidates were expressed in the E. coli and wheat germ cell-free systems at a 50 μl scale. Products were affinity purified in a single-step and coupled to luminex beads to measure antibody reactivity of human immune sera.Both systems readily produced detectable proteins; proteins produced in wheat germ, however, were mostly soluble and intact as opposed to proteins produced in E. coli, which remained mostly insoluble and highly degraded. Noticeably, wheat germ proteins were recognized in significantly higher numbers by sera of P. vivax patients than identical proteins produced in E. coli.The wheat germ cell-free system offers the possibility of expressing soluble P. vivax proteins in a small-scale for antigen discovery and immuno-epidemiological studies using suspension array technology.The recent call for malaria eradication has re-emphasized the importance of bringing Plasmodium vivax into the research agenda [1]. Plasmodium vivax remains the most widely distributed human malaria parasite with 2.85 billion people living at risk of infection [2]. Noticeably, the number of yearly clinical cases seems to be increasing from 70-80 million [3] to 300 million cases [4] and these include cases of severe disease and death exclusively associated with P. vivax [5,6]. Moreover, experts agree that present tools against Plasmodium falciparum will not be effective against P. vivax, reinforcing the development of control measurements for this species [7]. Among these tools, vaccines continue to represent the most cost-effective control measurement but unfortunately vaccine development in P. vivax lags well behind that of P. falciparum [8].The genomes of human malaria parasites encode approximately 5,400 coding genes opening an avenue for antigen discovery in this species [9]. Unfortunately, cell-based expression systems have met limited success to obtain soluble proteins largely attributed to the high AT-content, the ex