Anti-merozoite surface protein-1 19-kDa IgG in mother-infant pairs naturally exposed to Plasmodium falciparum: Subclass analysis with age, exposure to asexual parasitemia, and protection against malaria. V. The Asembo Bay Cohort Project

The anti-merozoite surface protein-1 19-kDa IgG (anti-MSP1(19KD)) IgG respo nses of 33 parasitemic infants, aged 6-14 months, were compared with those of their mothers at the time of the infant's delivery and at the time the i nfants were sampled; the antimalaria protection associated with these respo nses was also compared. IgG1 and IgG3 were the predominant subclasses. Infa nts <300 days old and pregnant mothers had the lowest cytophilic-to-noncyto philic IgG ratio. By 300 days of age, the infants had IgG subclass composit ions and levels similar to those of their mothers at the same date. Among i nfants, older infants with only 1 or 2 detected asexual parasitemias had th e highest cytophilic-to-noncytophilic IgG ratio and IgG1 levels. IgG1 level was negatively correlated with protection. The findings suggest that the M SP1(19KD) antibody response develops with age, not with multiple experience s with parasitemia, and, thus, that an antimalaria vaccine strategy for pre gnant mothers could delay infants' first parasitemias until they are more c apable of mounting a favorable anti-MSP1(19KD) response.