Antigenicity and immunogenicity of recombinant glutamate-rich protein of Plasmodium falciparum expressed in Escherichia coli.

A recombinant Plasmodium falciparum glutamate-rich protein (GLURP) was produced in Escherichia coli as a nearly full-length protein. In order to map immunodominant regions on GLURP, the nonrepetitive amino-terminal region (R0) as well as the central repeat region (R1) and the carboxy-terminal repeat region (R2) were also produced as separate products. All four purified gene products reacted specifically with serum samples from adults living in an area of Liberia where malaria is holoendemic. It appears that the human immune response against GLURP is primarily directed against the R2 region because 94% of the serum samples reacted with this region in an immunoassay. Antibody reactivity against the R0 region was also observed in 75% of the serum samples, while the R1 region showed only weak antibody-binding activity. When the nearly full-length GLURP molecule was adsorbed to Al(OH)3 it was found to be immunogenic in mice. In these experiments, the antibody response was almost exclusively directed against the R2 region. When anti-GLURP sera were obtained from rabbits immunized with the three regions, R0, R1, and R2, respectively, they recognized in immunoprecipitation experiments authentic GLURP from P. falciparum grown in vitro. These results demonstrate that GLURP produced in E. coli can induce a humoral immune response against GLURP derived from blood-stage parasites.