A Plasma Survey Using 38 PfEMP1 Domains Reveals Frequent Recognition of the Plasmodium falciparum Antigen VAR2CSA among Young Tanzanian Children

PfEMP1 proteins comprise a family of variant antigens that appear on the surface of P. falciparum-infected erythrocytes and bind to multiple host receptors. Using a mammalian expression system and BioPlex technology, we developed an array of 24 protein constructs representing 38 PfEMP1 domains for high throughput analyses of receptor binding as well as total and functional antibody responses. We analyzed the reactivity of 561 plasma samples from 378 young Tanzanian children followed up to maximum 192 weeks of life in a longitudinal birth cohort. Surprisingly, reactivity to the DBL5 domain of VAR2CSA, a pregnancy malaria vaccine candidate, was most common, and the prevalence of reactivity was stable throughout early childhood. Reactivity to all other PfEMP1 constructs increased with age. Antibodies to the DBL2βC2PF11_0521 domain, measured as plasma reactivity or plasma inhibition of ICAM1 binding, predicted reduced risk of hospitalization for severe or moderately severe malaria. These data suggest a role for VAR2CSA in childhood malaria and implicate DBL2βC2PF11_0521 in protective immunity

Prevalence of plasma IgG reactivity to individual PfEMP1 domains, stratified by age.

<p>Bars indicate the prevalence of plasma IgG reactivity among Tanzanian children of different ages to the indicated PfEMP1 constructs. PfEMP1 classification: V2 - VAR2CSA, A - group A, B - group B, C - group C, B/C - group B/C (according to <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0031011#pone.0031011-Lavstsen1" target="_blank">[29]</a>). As indicated in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0031011#pone-0031011-g001" target="_blank">Figure 1</a> and <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0031011#pone-0031011-t001" target="_blank">Table 1</a>, DBL1-containing constructs also contain N-terminal segment (NTS), but NTS is not included in the construct names.</p

Plasma IgG reactivity to PfEMP1 domains is dynamic over time in individual children.

<p>The two panels portray two children as representative examples who experience increases and decreases in plasma reactivity over time against two commonly recognized PfEMP1 domains.</p

PfEMP1 domains tested for IgG reactivity using Tanzanian children's plasma.

<p>PfEMP1 domain constructs studied in this work are indicated by boxes. Shaded boxes indicate constructs recognized by ≥10% of children. <i>Var</i> gene groups according to (25) and total numbers of PfEMP1 genes from parasite clone 3D7 genome in these groups are shown on the left.</p

Levels of CD36 binding to N-terminal head structures (NTS-DBL1-CIDR1) or their CIDR1 domains (CIDR1).

<p>*Domains cloned into pAdEx, other domains cloned into pHisAdEx.</p><p>Abbreviations: AU, Arbitrary Units; SD, Standard Deviation; NT, Not Tested.</p

Number of children hospitalized with subsequent severe or moderately severe malaria, stratified by Positive plasma reactivity (IgG>0 or BI>0) against DBL2βC2_{PF11_0521} domain measured at 76 weeks of age.

<p>Fisher's Exact Text: p = 0.048, OR = 0.117 [95% CI = 0.007 to 1.98].</p><p>Please, note that the P value computed from Fisher's test is exactly correct. However, the confidence intervals for the Odds ratio (OR) are computed by methods that are only approximately correct. Because one cell contains “0”, a value of 0.5 was automatically added to each cell for calculation of OR (GraphPad Prizm software). Therefore, the confidence interval does not quite agree with the P value.</p