A LONGITUDINAL-STUDY OF TYPE-SPECIFIC ANTIBODY-RESPONSES TO PLASMODIUM-FALCIPARUM MEROZOITE SURFACE PROTEIN-1 IN AN AREA OF UNSTABLE MALARIA IN SUDAN

Merozoite surface protein-1 (MSP-1) of Plasmodium falciparum is a mala ria vaccine candidate Ag, immunity to MSP-1 has been implicated in pro tection against infection in animal models. However, MSP-1 is a polymo rphic protein and its immune recognition by humans following infection is not well understood. We have compared the immunogenicity of conser ved and polymorphic regions of MSP-1, the specificity of Ab responses to a polymorphic region of the Ag, and the duration of these responses in Sudanese villagers intermittently exposed to P. falciparum infecti ons, Recombinant Ags representing the conserved N terminus (Block 1), the conserved C terminus, and the three main types of the major polymo rphic region (Block 2) of MSP-1 were used to determine the specificity and longitudinal patterns of IgG Ab responses to MSP-1 in individuals . Abs from 52 donors were assessed before, during, and after malaria t ransmission seasons for 4 yr, Ags from the Block 1 region were rarely recognized by any donor, Responses to the C-terminal Ag occurred in th e majority of acutely infected individuals and thus were a reliable in dicator of recent clinical infection. Ags from the polymorphic Block 2 region of MSP-1 were recognized by many, although not all individuals after clinical malaria infections, Responses to Block 2 were type spe cific and correlated with PCR typing of parasites present at the time of infection, Responses to all of these Ags declined within a few mont hs of drug treatment and parasite clearance, indicating that naturally induced human Ab responses to MSP-1 are short lived.