Figure 3. Systemic inflammation coincides with the onset of clinical symptoms.

(A) Parasite growth curves colour-coded by host response; each line represents one volunteer. Blood samples were collected every 12 hr for qPCR analysis of circulating parasite density and the horizontal green line represents the lower limit of quantification (20 parasites ml⁻¹). (B) Parasite multiplication rates colour-coded by host response; each dot represents one volunteer and shaded areas show the mean value. A Mann Whitney test was used to ask whether the parasite multiplication rate observed in the inflammatory group was different to all other volunteers (p value is shown). (C and D) Linear regression of CXCL10 (C) or parasite multiplication rate (D) plotted against clinical score (the sum of adverse events during infection). CXCL10 fold-change measures plasma concentration at diagnosis over baseline (day −1). One dot represents one volunteer (no data for v020) and dots are colour-coded by host response. The green line represents the best-fit model (p value of the slope is shown) and dashed lines are the 95% confidence intervals. (E) Log10 transformed intensity values of adenosine in plasma during infection. An authentic standard was run in tandem with all samples to validate adenosine detection. (F) Range-scaled intensity values of 10 plasma metabolites that were differentially abundant during infection. Metabolites (rows) and samples (columns) are ordered by hierarchical clustering. Note that an authentic standard was used to validate detection of all underlined metabolites and the full name for oxoglutaric acid is 4-hydroxy-2-oxoglutaric acid. (E and F) Only plasma samples from the most inflammatory and symptomatic volunteers (v016, v017, and v013), the suppressor volunteers (v022 and v019) and two unresponsive volunteers (v018 and v208) were analysed for metabolite abundance.

Figure 3—figure supplement 1. Adverse events after blood challenge.

Data on symptoms were collected every 12 hr from day 2 post-infection either on diary cards (self-reporting) or during clinic visits. Adverse events were graded as mild (transient or mild discomfort – no medical intervention required); moderate (mild to moderate limitation in activity – no or minimal medical intervention required); or severe (marked limitation in activity – may require medical intervention).

Figure 3—figure supplement 2. Inflammation is linked to hallmark symptoms of malaria.

(A) Proportion of mild, moderate and severe adverse events at diagnosis. For each volunteer, adverse events were recorded for 13 clinical categories and these were summed to give a clinical score at diagnosis (mild = 1, moderate = 2 and severe = 3). A Fisher’s exact test was then used to assess the significance of the difference in clinical score between the inflammatory group and unresponsive/suppressor hosts (p value is shown and n = total number of data-points recorded). The maximum core body temperature measured in any volunteer within a group is shown in each doughnut plot. (B) Plasma concentration of Angiopoietin-2 comparing pre-infection (open circle) and diagnosis (filled circle) samples. Each dot represents one volunteer and dots are colour-coded by host response. The green line represents the mean reference value measured in healthy human donors (heparin plasma samples). (C) Lymphocyte counts in whole blood during infection; each line represents one volunteer and lines are colour-coded by host response. Data are shown as fold-change over baseline (day −1). A Mann Whitney test was used to assess the significance of differences in cell counts between inflammatory volunteers and all other hosts at diagnosis (p value is shown). (D) Five-part differential whole blood counts comparing pre-infection and diagnosis samples. Volunteer numbers are inset into stacked bars and samples are ordered by host response followed by time-point.

Figure 3—figure supplement 3. A conserved early metabolic signature of falciparum malaria.

Volcano plot showing the 10 plasma metabolites that were differentially abundant during infection. We grouped unresponsive (v018 and v208), inflammatory (v016, v017 and v013), and suppressor (v022 and v019) hosts and grouped two post-infection time-points (day 8 and diagnosis) to identify a conserved and persistent signature, respectively. These samples (n = 14) were tested against pre-infection plasma (n = 7) using an FDR-corrected p value < 0.1. A positive intensity ratio indicates metabolites are more abundant during infection, whereas a negative ratio indicates metabolite depletion. Vertical black dotted lines represent a 1.5-fold change in abundance. Squares with a solid black border show that an authentic standard was run in tandem with the samples to validate metabolite detection.