Expression profiling by high throughput sequencing
Summary
Controlled human malaria infection is a powerful experimental medicine tool to understand the human immune response to a first ever malaria infection. Here we have taken this approach a step further and conducted the first human malaria reinfection trial in the modern era. Volunteers were challenged up to three times with Plasmodium falciparum in 4- to 8-month intervals. Remarkably, parasite densities and the dynamics of blood-stage infection were not altered over the course of three homologous infections. Using whole blood RNA-sequencing we tracked the host immune response through time and found that the emergency myeloid response, which triggers systemic inflammation and the global recruitment of T cells into lymphoid tissues, is not altered by repeated infection. Six days after parasite clearance, when the innate response subsides, T cells return to the circulation and reflect the outcome of critical cell-cell interactions within the inflamed spleen. By transcriptionally profiling flow sorted CD4+ T cell subsets after their release from the tissue we could show that TH1 polarised effector response in naïve hosts is tolerised upon re-challenge to avoid collateral tissue damage. Instead, a subset of specialised cytokine-producing CD4+ T cells are activated to promote essential protective immune functions. Together these data indicate that innate and adaptive immune responses can be uncoupled in malaria and illustrate that human hosts prioritises damage limitation (tolerance) over parasite clearance (resistance) to quickly acquire clinical immunity.
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