Longevity of naturally acquired antibody responses to the N- and C-terminal regions of Plasmodium vivax merozoite surface protein 1.

In an earlier study, we found that individuals with patent infection had significantly higher IgG antibody titers to the 19-kD C-terminal region of Plasmodium vivax merozoite surface protein 1 (PvMSP1) than individuals treated for malaria 1-4 months earlier. These results suggested that the antibody levels decreased rapidly following treatment. The present study was designed to determine the persistence of antibody response to the N- and C-terminal regions of PvMSP1 after infection with P. vivax in individuals from the city of Bélem in northern Brazil. Our results demonstrated that the vast majority of individuals had a significant decrease in antibody titers to the C-terminal region of PvMSP1 in a period of two months following treatment. Among responders to the C-terminal region, 44.4% became serologically negative and 44.4% had their antibody titers reduced by an average of 13-fold. Only 11.2% of the individuals had their antibody titers maintained or slightly increased during that period. A decrease in the antibody response to the recombinant protein representing the N-terminal region of PvMSP1 was also noted; however, it was not as dramatic. The rapid decrease in the antibody levels to the C-terminal region of PvMSP1 might contribute to the high risk of reinfection in these individuals.