title: Acquisition of antibodies against Plasmodium falciparum merozoites and malaria immunity in young children and the influence of age, force of infection, and magnitude of response.
abstract: Individuals in areas of Plasmodium falciparum endemicity develop immunity to malaria after repeated exposure. Knowledge of the acquisition and nature of protective immune responses to P. falciparum is presently limited, particularly for young children. We examined antibodies (IgM, IgG, and IgG subclasses) to merozoite antigens and their relationship to the prospective risk of malaria in children 1 to 4 years of age in a region of malaria endemicity in Papua New Guinea. IgG, IgG1, and IgG3 responses generally increased with age, were higher in children with active infection, and reflected geographic heterogeneity in malaria transmission. Antigenic properties, rather than host factors, appeared to be the main determinant of the type of IgG subclass produced. High antibody levels were not associated with protection from malaria; in contrast, they were typically associated with an increased risk of malaria. Adjustment for malaria exposure, using a novel molecular measure of the force of infection by P. falciparum, accounted for much of the increased risk, suggesting that the antibodies were markers of higher exposure to P. falciparum. Comparisons between antibodies in this cohort of young children and in a longitudinal cohort of older children suggested that the lack of protective association was explained by lower antibody levels among young children and that there is a threshold level of antibodies required for protection from malaria. Our results suggest that in populations with low immunity, such as young children, antibodies to merozoite antigens may act as biomarkers of malaria exposure and that, with increasing exposure and responses of higher magnitude, antibodies may act as biomarkers of protective immunity.
authors.affiliation: Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria, Australia Papua New Guinea Institute of Medical Research, Papua New Guinea Institute for Glycomics, Griffith University, Southport, Queensland, Australia.
authors.forename: Danielle I
authors.initials: DI
authors.lastname: Stanisic
authors.affiliation: Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria, Australia Burnet Institute for Medical Research and Public Health, Melbourne, Victoria, Australia.
authors.forename: Freya J I
authors.initials: FJ
authors.lastname: Fowkes
authors.affiliation: Papua New Guinea Institute of Medical Research, Papua New Guinea.
authors.forename: Melanie
authors.initials: M
authors.lastname: Koinari
authors.affiliation: Papua New Guinea Institute of Medical Research, Papua New Guinea.
authors.forename: Sarah
authors.initials: S
authors.lastname: Javati
authors.affiliation: Papua New Guinea Institute of Medical Research, Papua New Guinea.
authors.forename: Enmoore
authors.initials: E
authors.lastname: Lin
authors.affiliation: Papua New Guinea Institute of Medical Research, Papua New Guinea.
authors.forename: Benson
authors.initials: B
authors.lastname: Kiniboro
authors.affiliation: Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria, Australia Burnet Institute for Medical Research and Public Health, Melbourne, Victoria, Australia.
authors.forename: Jack S
authors.initials: JS
authors.lastname: Richards
authors.affiliation: Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria, Australia Papua New Guinea Institute of Medical Research, Papua New Guinea.
authors.forename: Leanne J
authors.initials: LJ
authors.lastname: Robinson
authors.affiliation: Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria, Australia.
authors.forename: Louis
authors.initials: L
authors.lastname: Schofield
authors.affiliation: Case Western Reserve University, Cleveland, Ohio, USA.
authors.forename: James W
authors.initials: JW
authors.lastname: Kazura
authors.affiliation: Case Western Reserve University, Cleveland, Ohio, USA.
authors.forename: Christopher L
authors.initials: CL
authors.lastname: King
authors.affiliation: Case Western Reserve University, Cleveland, Ohio, USA.
authors.forename: Peter
authors.initials: P
authors.lastname: Zimmerman
authors.affiliation: Swiss Tropical Institute and Public Health Institute, Basel, Switzerland University of Basel, Basel, Switzerland.
authors.forename: Ingrid
authors.initials: I
authors.lastname: Felger
authors.affiliation: Papua New Guinea Institute of Medical Research, Papua New Guinea.
authors.forename: Peter M
authors.initials: PM
authors.lastname: Siba
authors.affiliation: Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria, Australia Papua New Guinea Institute of Medical Research, Papua New Guinea Barcelona Centre for International Health Research (CRESIB), Barcelona, Spain ivomueller@fastmail.fm beeson@burnet.edu.au.
authors.forename: Ivo
authors.initials: I
authors.lastname: Mueller
authors.affiliation: Burnet Institute for Medical Research and Public Health, Melbourne, Victoria, Australia Department of Microbiology, Monash University, Victoria, Australia ivomueller@fastmail.fm beeson@burnet.edu.au.
authors.forename: James G
authors.initials: JG
authors.lastname: Beeson
mesh_terms: D000367:Age Factors; D000913:Antibodies, Protozoan / Q000276:immunology*; D000953:Antigens, Protozoan / Q000276:immunology*; D002675:Child, Preschool; D015331:Cohort Studies; D005260:Female; D006801:Humans; D007074:Immunoglobulin G / Q000097:blood / Q000145:classification / Q000276:immunology; D007075:Immunoglobulin M / Q000097:blood / Q000276:immunology; D007223:Infant; D016778:Malaria, Falciparum / Q000276:immunology* / Q000382:microbiology / Q000635:transmission; D008297:Male; D052940:Merozoites / Q000276:immunology*; D010219:Papua New Guinea; D010963:Plasmodium falciparum / Q000276:immunology*; D015800:Protozoan Proteins / Q000276:immunology
chemical_list: D000913:Antibodies, Protozoan; D000953:Antigens, Protozoan; D007074:Immunoglobulin G; D007075:Immunoglobulin M; D015800:Protozoan Proteins