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Inducible mechanisms of disease tolerance provide an alternative strategy of acquired immunity to malaria.

ABSTRACT: Disease tolerance is an important alternative strategy for rapidly acquired immunity to malaria. We show that tolerance is induced by a single malaria episode - in the absence of parasite clearance. Inflammatory spleen monocytes from C57Bl6/J mice with memory of malaria infection dramatically change their transcriptional response to a second infection; instead of driving emergency inflammation they promote stress and tissue tolerance (RNAseq data available in GEO series GSE150047). This unique functional profile is not underpinned by alterations in the epigenetic landscape of inflammatory monocytes before their release from the bone marrow (ChIPseq data available in GEO series GSE150478) - tolerance is therefore imprinted within the spleen (microarray data available in GEO series GSE149894). Hosts thus acquire long-lasting mechanisms that control inflammation (reducing collateral tissue damage) and learn to actively promote stress tolerance (protecting tissues against toxic products and processes) after one malaria episode.

ORGANISM(S): Mus musculus

PROVIDER: GSE150479 | GEO | 2020/11/26

REPOSITORIES: GEO

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Project description:Disease tolerance is an alternative strategy for acquired immunity to malaria and can be rapidly induced after a single malaria episode - in the absence of improved parasite clearance. Memory of a first malaria episode dampens the inflammatory profile of spleen monocytes and induces mechanisms of stress tolerance to minimise tissue damage. This begs the question how monocytes are instructed to respond in a different way to second compared to first malaria infection. We asked if malaria alters the epigenetic landscape of inflammatory monocytes before their release from the bone marrow - thus testing the compelling innate memory hypothesis. We compared the genome-wide distribution of histone modifications on flow-sorted bone marrow monocytes from mice with memory of severe mosquito transmitted P. chabaudi AJ infection (30 days after drug cure) and drug treated uninfected age-matched controls using ChIPseq. Specifically, we tested whether once-infected mice have long-lived modifications in i) transcription start sites marked with H3K27ac to activate transcription ii) enhancers or superenhancers marked with H3K4me1 to promote gene expression and iii) in H3K9me3 to condense DNA into heterochromatin thereby silencing gene expression. We found no meaningful differences in the histone modification profiles of 2848 genes that define monocyte function in first and second malaria infection using the motif discovery software HOMER. Furthermore, when calling differentially modified regions (DMR) between once-infected mice and uninfected mice to ask whether there were any measurable differences in the epigenetic landscapes of these genes, we found 95% had no detectable modifications. In those rare cases where a DMR was called, HOMER assigned a low peak score, indicating low confidence and minimal biological relevance. Epigenetic reprogramming does therefore not underpin the functional specialisation of inflammatory monocytes in tolerised hosts. Innate memory is thus not induced by malaria infection in vivo. Instead, altered monocyte function and fate are imprinted within the spleen (link to GEO microarray) to promote disease tolerance.

Project description:Genome wide DNA methylation profiling of isolated monocyte samples from healthy Kenyan children, the same children during an episode of acute malaria, healthy Kenyan adults, and healthy adults from the United States. The Illumina Infinium MethylationEPIC BeadChip microarray was used to obtain DNA methylation profiles across approximately 860,000 CpGs in negatively selected monocyte samples. Samples included monocytes from 8 children from western Kenya obtained while healthy and matching samples from the same 8 Kenyan children obtained during an episode of acute uncomplicated Plasmodium falciparum malaria, 8 healthy malaria-immune adults from western Kenya, and 8 healthy malaria-naive adults from the US. Abstract -- Background: Age-related changes in adaptive and innate immune cells have been associated with a decline in effective immunity and chronic, low-grade inflammation. Epigenetic, transcriptional, and functional changes in monocytes occur with aging, though most studies to date have focused on differences between young adults and the elderly in populations with European ancestry; few data exist regarding changes that occur in circulating monocytes during the first few decades of life or in African populations. We analyzed DNA methylation profiles, cytokine production, and inflammatory gene expression profiles in monocytes from young adults and children from western Kenya. Results: We identified several hypo- and hyper-methylated CpG sites in monocytes from Kenyan young adults vs. children that replicated findings in the current literature of differential DNA methylation in monocytes from elderly persons vs. young adults across diverse populations. Differentially methylated CpG sites were also noted in gene regions important to inflammation and innate immune responses. Monocytes from Kenyan young adults vs. children displayed increased production of IL-8, IL-10, and IL-12p70 in response to TLR4 and TLR2/1 stimulation as well as distinct inflammatory gene expression profiles. Conclusions: These findings complement previous reports of age-related methylation changes in isolated monocytes and provide novel insights into the role of age-associated changes in innate immune functions.

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Inducible mechanisms of disease tolerance provide an alternative strategy of acquired immunity to malaria.

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