Antibody levels in Tanzanian children. (A) The figure shows the overall frequency distribution of log-transformed naturally acquired anti-PfEMMA1 fragment 1 antibody concentrations measured approximately every 6 mo and at sick visits. The curve has a normal distribution; the dashed line denotes the 97.5th percentile, the only threshold among several tested that predicted lower parasite densities. (B) The plots show the relationship between antibodies to PfEMMA1 fragment 1 (frag 1), PfMSP1, PfMSP3, PfMSP7, PfLSA-N, and PfLSA-C and parasite densities in Tanzanian children. We measured IgG antibody levels to PfMSP1 (19-kD region of the 3D7 strain; BEI Resources/MR4), PfMSP3 (aa 99–265), PfMSP7 (aa 117–248), PfLSA-N (aa 28–150), and PfLSA-C (aa 1,630–1,909) using available plasma from 225 2-yr-old children enrolled in the Tanzanian birth cohort. The frequencies of contacts with children who had antibody levels ≤97.5th percentile vs. >97.5th percentile were as follows: PfEMMA1 fragment 1, 14,076 vs. 646; PfMSP1-19, 3,186 vs. 95; PfMSP3, 3,202 vs. 79; PfMSP7, 3,183 vs. 98; PfLSA-N, 3,181 vs. 100; and PfLSA-C, 3,203 vs. 78. RRs for these proteins are as follows: PfEMMA1 fragment 1, 0.54 (95% CI, 0.30–0.97, *, P = 0.038); PfMSP1-19, 2.04 (0.92–4.51, P = 0.08), PfMSP3, 0.38 (0.15–1.00, **, P = 0.05); PfMSP7, 0.63 (0.14–2.79, P = 0.54); PfLSA-N, 2.36 (1.05–5.31, P = 0.04); and PfLSA-C, 2.36 (1.15–4.81, P = 0.02). All analyses used multivariable GEE modeling.