A fusion protein, derived from P. falciparum Glutamate-rich protein (GLURP)genetically coupled to P. falciparum Merozoite surface protein 3 (MSP3) wasproduced in Lactococcus lactis as a secreted recombinant GLURP-MSP3 hybridprotein and experiments showed that the GLURP-part of the hybrid increased theoverall antibody response. Immunizations with the hybrid protein consistentlygenerated a stronger antibody response against the individual GLURP and MSP3domains than a mixture of the two recombinant molecules injected at one siteor the individual recombinant molecules injected simultaneously at twodifferent sites. The difference was most pronounced for the MSP3-specificantibody response suggesting that T cell epitopes located in the GLURP RO-region provide help for B-cell epitopes in the MSP3 region. Moreover, when theanimals were injected with a mixture of GLURP and MSP3, individual mice tendedto mount a predominant antibody response against either molecule: in someanimals GLURP was immuno~dominant whereas in other animals MSP3 was thedominant immunogen. Additionally, the hybrid was also more antigenic than theindividual recombinant proteins since the ELISA-titer of naturally occurringIgG antibodies, in clinically immune African adults, against the hybridprotein was higher than the titers against the individual recombinantproteins. The hybrid protein was also demonstrated to be a potentialprotective antigen as mouse anti-GLURP-MSP3 IgG antibodies were able toinhibit parasite-growth in vitro in a monocyte-dependent manner.
