Isotypes of naturally acquired antibodies to a repetitive & non-repetitive epitope on Plasmodium falciparum surface proteins in an endemic area of Sri Lanka.

Isotypes of antibodies in adults and 7-15 yr old children living in a malaria endemic area of Sri Lanka were measured by radioimmunoassay against synthetic target antigens derived from two Plasmodium falciparum surface proteins. Greater than 50 per cent of the sample population possessed IgM antibodies while < or = 13 per cent developed each of the IgG antibody isotypes against a repetitive epitope present on the circumsporozoite protein (CS repeat). A more even distribution of IgM, IgG1, IgG2, IgG3 and IgG4 antibodies was seen against a non-repetitive epitope (P103) on a 45 kDa merozoite surface protein. This difference is attributed to a T-independent antibody response against the CS repeat.

Dynamics of natural antibody responses to malaria parasite surface proteins in the intermediate rainfall zone of Sri Lanka.

Antibodies against repetitive epitopes on Plasmodium falciparum and P. vivax circumsporozoite (CS) proteins and epitopes on the 45 kDa and 185-200 kDa P. falciparum merozoite surface proteins were measured by radioimmunoassay in a two year longitudinal study in Nikawehera village located in the intermediate rainfall zone of Sri Lanka. The prevalence and concentrations of specific antibodies were in many, but not all instances, greater in adults than in children who were aged 7-15 yr at the beginning of the study. The concentrations and prevalence of antibodies were associated with malaria transmission levels previously determined from entomological and hospital admission data in the area. Antibody responses to epitopes on different P. falciparum antigens, two different epitopes within the 185-200 kDa merozoite surface protein and between the P. falciparum and P. vivax CS repeats were significantly correlated. Antibody concentrations against a conserved epitope in the 185-200 kDa protein were significantly higher in P. falciparum infected individuals than in non-parasitaemic subjects. Antibody concentration and prevalences in Nikawehera were lower than at Weheragala, a site located 70 km away in the dry zone of Sri Lanka. It is postulated that lower levels of immunity in the population in areas such as Nikawehera, that are adjacent to more highly malaria endemic areas, may promote epidemics when conditions favour transmission.