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.