<i>Var</i> transcription profiles of parasites recovered from infected volunteers at the day of first microscopically detectable parasitemia.

Abstract

<p>(A) Heat map showing the individual <i>var</i> gene expression for all volunteer samples taken when parasites were present in the thick blood smear ranked by mean expression. To correct for individual differences in the overall <i>var</i> expression levels, the expression for each <i>var</i> gene was normalized against the total <i>var</i> expression in each sample. The color scale indicates the relative expression levels with red representing values above the median, blue representing values below the median, and white representing median. Grey means not detected. The number of sporozoites (200, 800, 2500 and 3200) and mode of injection (iv = intravenous, id = intradermal) used for each volunteer are indicated below. (B) The distribution of the relative gene expression per <i>var</i> gene and control genes is shown in a dot plot for all volunteer samples at the day of patent infection defined as parasites present in the thick blood smear (n = 18). Each point represents a <i>var</i> gene expression value relative to the normalizing gene <i>sbp1</i> observed per volunteer sample and the median expression per <i>var</i> gene is marked. Housekeeping genes used as controls, <i>var</i> gene names and groups are indicated. (C) Proportion of <i>var</i> gene expression by group across all volunteers at the day of patent infection. For comparison, genomic proportion of each <i>var</i> gene group is indicated after the color code. (D) Comparison of the expression levels between subtelomeric and centromeric <i>var</i> gene variants. The box plot shows the distribution of transcript levels for each individual <i>var</i> gene relative to <i>sbp1</i> according to the chromosomal localization of the genes for all 18 volunteer samples at the day of patent infection. Gene expression varied significantly between both gene sets (Wilcoxon rank-sum test, p<0.0001) with median expression of 232 (IQR: 87–510) for telomeric <i>var</i> genes and 40 (IQR: 18–94) for centromeric <i>var</i> genes. (E) The heat map of pairwise Spearman’s rank correlation coefficients (R) between expression profiles illustrates the positive correlation between all 18 volunteer samples at the day of patent infection. Volunteer samples were ranked by the sum of their correlation coefficients. The color scale indicates the correlation coefficient in the range from 0 to 1. With exception of isolate 25.1 versus the isolates 02.1 (p = 0.0015), 25.3 (p = 0.0029) and 32.4 (p = 0.0030) all expressions correlated at a significance level below 0.001.</p