Merozoite surface protein-1 (MSP-1) of Plasmodium falciparum is a
malaria vaccine candidate Ag. Immunity to
MSP-1 has been implicated in protection against
infection in animal models. However,
MSP-1 is a polymorphic
protein and its immune recognition by humans following
infection is not well understood. We have compared the immunogenicity of conserved 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
infections. Recombinant Ags representing the conserved N terminus (Block 1), the conserved C terminus, and the three main types of the major polymorphic 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 transmission seasons for 4 yr. Ags from the Block 1 region were rarely recognized by any donor. Responses to the C-terminal Ag occurred in the majority of acutely infected individuals and thus were a reliable
indicator 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 specific and correlated with PCR typing of parasites present at the time of
infection. Responses to all of these Ags declined within a few months of
drug treatment and parasite clearance, indicating that naturally induced human Ab responses to
MSP-1 are short lived.