IgG3 antibodies to Plasmodium falciparum merozoite surface protein 2 (MSP2): increasing prevalence with age and association with clinical immunity to malaria.

In a cross-sectional survey carried out in west Africa (The Gambia), where Plasmodium falciparum malaria is endemic with seasonal transmission, 178 individuals 1-75 years of age were assessed for their antibody response to the malaria vaccine candidate, merozoite surface protein 2 (MSP2). Total IgG to recombinant antigens representing full-length, repetitive, and group-specific domains of both allelic families of MSP2 was determined by ELISA. The IgG-subclass profile of IgG-positive sera was assessed. Antibody prevalence was age-dependent, reaching a peak during adolescence. In MSP2-seropositive individuals, there was a predominance of cytophilic antibodies (IgG1 and IgG3); IgG1 antibodies were prevalent in children less than 10 years of age, whereas in adolescents and adults MSP2-specific antibodies were predominantly IgG3. In parallel, we conducted a longitudinal study of children (3-8 years of age) from the same community; sera collected before the malaria transmission season were tested for the presence of anti-MSP2 antibodies. The subsequent susceptibility of these children to clinical malaria was monitored and the association between anti-MSP2 antibodies of different IgG subclasses and resistance to clinical malaria was tested. The presence of IgG3 antibodies to MSP2 serogroup A was negatively associated with the risk of clinical malaria whereas IgG1 antibodies to MSP2 serogroup B were associated with an increased risk of clinical infection. Our data suggest that age/exposure-related acquisition of IgG3 antibodies to MSP2 may contribute to the development of clinically protective immunity to malaria.