A LONGITUDINAL-STUDY OF NATURALLY ACQUIRED CELLULAR AND HUMORAL IMMUNE-RESPONSES TO A MEROZOITE SURFACE PROTEIN (MSP1) OF PLASMODIUM-FALCIPARUM IN AN AREA OF SEASONAL MALARIA TRANSMISSION

A longitudinal study of cellular and serological responses to the major merozoite surface protein of Plasmodium falciparum (PfMSP1) has been conducted in a malaria immune population living in The Gambia, where malaria transmission is seasonally endemic. Recombinant or native proteins representing the sequence of PfMSPI from the Wellcome strain of P. falciparum were used in in vitro lymphocyte proliferation, cytokine and antibody assays. Cellular responses of individual donors fluctuated over time, independent of seasonal changes in malaria transmission whereas anti-PfMSP1 antibody levels were remarkably stable. At a population level, IFNgamma responses were both more prevalent and of greater magnitude at the end of the rainy (malaria transmission) season than during the dry season. Responses of individuals living in a rural village were compared with those of individuals living in an urban area with much lower levels of malaria transmission. Malaria infections were more likely to be symptomatic in urban dwellers than in inhabitants of rural villages but no significant differences in the level or prevalence of cellular or serological responses were seen between the two groups. However, urban dwellers with current symptomatic malaria infections had somewhat lower anti-PfMSP1 antibody levels than their healthy, non-parasitaemic neighbours.