A LONGITUDINAL INVESTIGATION OF IGG AND IGM ANTIBODY-RESPONSES TO THEMEROZOITE SURFACE PROTEIN-1 19-KILODALTON DOMAIN OF PLASMODIUM-FALCIPARUM IN PREGNANT-WOMEN AND INFANTS - ASSOCIATIONS WITH FEBRILE ILLNESS, PARASITEMIA, AND ANEMIA

This study was aimed at delineating characteristics of naturally acqui red immunity against the merozoite surface antigen-1 (MSP-1) of Plasmo dium falciparum, a candidate malaria vaccine antigen, A case/control s tudy was performed on 75 case/control pairs of infants with febrile il lness at the time of the first detected infection indicating a clinica l case. The presence and level of antibodies at one month prior to the first infection and at the time of the first infection in the afebril e group was significantly higher than in the febrile group. Decreased parasite density and decreased infection-related loss of hemoglobin wa s seen in infants with anti-MSP-1(19kD) IgG antibodies. In addition, m others who were positive for the presence of these antibodies conferre d protection against placental infection and infection in their infant s. In this study, development of anti-MSP-1(19kD) antibody responses i n 24 infants were studied longitudinally using monthly serum samples c ollected from birth until approximately one year of age. In addition, umbilical cord blood sera and respective mothers' sera were analyzed. Longitudinal studies of antibody responses revealed several short-live d IgG and IgM peaks throughout an infant's first year that correlated with detection of parasitemia. The protection against parasitemia and febrile illness was observed in infants when anti-MSP1-(19kD) antibodi es were present; when infants were negative for IgG, they had a 10-tim es greater risk of becoming parasitemic. These data from a longitudina l and prospective study of malaria suggest a protective role for anti- MSP-1(19kD) antibodies in infants and pregnant women.