Detection of antibodies to a 70 kDa Plasmodium falciparum exoantigen in malarious subjects using synthetic peptides.

Indirect fluorescent antibody (IFA) tests and enzyme-linked immunosorbent assays (ELISA) were used to measure antibodies to Plasmodium falciparum in patients with acute malaria from Bolivar State, Venezuela. Antibody titers increased significantly with repeated malarial episodes. IgG antibody responses to 4 synthetic peptides (termed C2, C3, C5, C10) derived from a 70 kDa P. falciparum (Indochina I/CDC strain) exoantigen were evaluated by a peptide-ELISA with overall positivity rates of 20%, 40%, 20% and 58%, respectively. Seropositivity to peptide C10 was consistently over 50% (range 53-75%) among patients of different ages. Overall IgM reactivity to the respective peptides was 53%, 30%, 83% and 70%. IgM reactivity was generally greater in patients with primary malarial infections. The ELISA is a useful adjunct to the IFA in measuring naturally-occurring antibodies to specific parasite proteins.