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

Background: In vitro cell-free systems for protein expression with extracts from prokaryotic (Escherichia coli) or eukaryotic (wheat germ) cells coupled to solid matrices have offered a valid approach for antigen discovery in malaria research. However, no comparative analysis of both systems is presently available nor the usage of suspension array technologies, which offer nearly solution phase kinetics. Methods: Five Plasmodium vivax antigens representing leading vaccine candidates were expressed in the E. coli and wheat germ cell-free systems at a 50 mu l scale. Products were affinity purified in a single-step and coupled to luminex beads to measure antibody reactivity of human immune sera. Results: 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. Conclusions: 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.