Fig. 5
Complement fixing antibodies are associated with reduced risk of P. falciparum placental infection and enhanced inhibition of pRBC binding to CSA. A Odds ratios for P. falciparum placental infection for complement C1q and C3 fixation levels stratified by P. falciparum infection status at enrolment, using logistic regression. Model included complement fixation as a continuous dependent variable, effect modification by P. falciparum peripheral infection status at enrolment (uninfected vs infected). Model includes additional adjustment for gravidity (primigravid vs multigravid), location of residence (town vs village), smoking (no vs yes), middle upper arm circumference in cm, gender of newborn (male vs female), hemoglobin levels (g/dl) at enrolment, South East Asian Ovalocytosis (wild type vs SAO) and α+thalassemia (wild type vs heterozygous/homozygous). A total of 140 uninfected and 71 P. falciparum infected (at enrolment ANC visit) individuals were included in the analysis of complement fixation on pRBCs and 141 uninfected and 71 P. falciparum infected individuals for complement fixation on VAR2CSA recombinant protein domains (VAR2CSA-DBL5 (3D7) & VAR2CSA-DBL3 (7G8)). Plots represent odds ratios for P. falciparum placental infection in individuals with high (75th percentile) and intermediate (50th percentile) complement fixing antibodies relative to low antibody levels (25th percentile) and bars represent 95% confidence intervals. Statistically significant associations (P<0.05) are shown in asterisks. B CS2 pRBCs binding to CSA was tested following opsonisation of CS2 pRBCs with 10% PNG antibody pool in the presence of NS, purified human C1q or C1q-depleted human serum. A malaria non-exposed antibody pool was used as a negative control. Plots represent median and interquartile range of pRBCs bound to CSA per mm2. Each data point represents an independent assay with 3–6 independent assays performed for each condition. All comparisons were statistically significant when compared to the non-exposed antibodies pool (P<0.04)