Comparative analysis of ELISAs employing repetitive peptides to detect antibodies to Plasmodium falciparum sporozoites.

In the last few years, a number of different recombinant and synthetic peptides consisting of the repetitive sequence of the Plasmodium falciparum circumsporozoite protein (NANP)n have been produced and used to develop immunoassays for the detection of antibodies against P. falciparum sporozoites in human sera. A comparative study of three enzyme-linked immunosorbent assays (ELISAs) that employed different (NANP)n peptides (the synthetic peptides (NANP)3 and (NANP)40 as well as the recombinant peptides R32tet32 and R32LR) was carried out using serum samples from individuals who were living in different malaria-endemic areas. The results obtained for these peptide-based ELISAs were compared with those obtained for an immunofluorescence assay (IFA) that used glutaraldehyde-fixed sporozoites. All the methods tested exhibited 100% specificity on sera from persons not exposed to malaria, good reproducibility (coefficients of variation ranged from 3% to 15% for peptide-based ELISAs), and good sensitivity. Reproducibility and sensitivity were lower for the IFA than for the peptide-based ELISAs, perhaps because of the subjective element in the interpretation of the results which is inherent in the IFA method. ELISAs based on peptides that contain a higher number of (NANP) repeats, i.e., (NANP)40 and R32tet32 or R32LR, gave results which correlated better with each other than with those obtained with the ELISA that employed a shorter (NANP)3 peptide. (NANP)n-based ELISAs are relatively simple and inexpensive methods for the detection of anti-P. falciparum sporozoite antibodies and can readily be used in epidemiological research in the field. These assays could contribute to a better understanding of the natural history of the host-parasite relationship in malaria research.