Antigenic cross-reactivity between different alleles of the Plasmodium falciparum merozoite surface protein 2.

The polymorphic domain of the gene encoding Plasmodium falciparum merozoite surface protein 2 (MSP2) was PCR amplified from blood of malaria patients, genotyped, and 19 distinct fragments were cloned and expressed in E. coli. The reactivity of naturally occurring antibodies against this panel of recombinant MSP2 antigens was tested using 67 homologous or heterologous sera from a serum bank of travel clinic patients. Sera from semi-immune individuals strongly recognized almost all recombinant antigens. Sera from primary infected patients either did not react at all (9 sera), or reacted weakly against varying numbers of antigens (39 sera). The antigens that showed reactions were mostly of the allelic family corresponding to the infecting clone, but in very few cases also of the alternative allelic family. Single clone infections and repeated samples from the same individual were analysed in greater detail. Thus, we were able to quantify cross-reactivity induced by a single P. falciparum infection. Within the two allelic families of MSP2, cross-reactivity was observed between some but not all alleles of the same family, whereas antibodies cross-reactive between variants belonging to different allelic families were detected in only a few cases.