The human immune response against the major merozoite surface antigen of Plasmodium falciparum.

The major surface antigen of the merozoite (MMSA) is very immunogenic in humans and it is considered a candidate for developing a malaria vaccine. This protein consists of conserved, dimorphic and polymorphic sequences that might differ in their ability to induce immunity. Epidemiological studies were undertaken in two different endemic areas of West Africa with the aim to identify the sequences within the protein that are the target of the humoral and cellular immune responses. Recombinant polypeptides expressed in E. coli, covering the conserved, the dimorphic and polymorphic regions, were used to evaluate the reactivity of sera and of Peripheral Blood Mononuclear Cells (PBMC) from inhabitants of rural communities exposed to P. falciparum transmission. The analysis of the humoral immune response against the MMSA showed that both qualitative and quantitative differences exist among groups of individuals with different susceptibility to P. falciparum infection. Furthermore, an association between intensity of transmission and antibody reactivity against the dimorphic regions was observed in individuals living in a malaria endemic area. The proliferative response of the PBMC was in most cases very low, however, several T cell clones could be established. The dimorphic region of MMSA was shown to contain T cell epitopes together with sequences most frequently recognized by human sera.