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Pulmonary parasite infection: do trypanosomes take your breath away?

ABSTRACT: Approximately 20% of sleeping sickness patients exhibit respiratory complications which are commonly attributed to secondary bacterial infections, with an unknown role of the parasite. Using a Glossina morsitans tsetse fly initiated Trypansoma brucei infection in mice we found that parasites rapidly and permanently colonize the lungs, representing one of the major target organs next to the adipose tissue. Trypanosomes were found by immunofluorescence staining and scanning electron microscopy to occupy the extravascular spaces surrounding the blood vessels of the alveoli and bronchi. Parasites were even found in the lung cartilage. Trypanosomes were often observed as nests of multiplying parasites exhibiting close interactions with collagen and highly active secretion of extracellular vesicles that are engaged in intercellular communication. The local immune response was analysed by flow cytometry after 10 and 21 days of infection and was characterized by a substantial increase of CD11b+ Ly6C+ monocytes, CD11b+ Ly6C+ F4/80+ macrophages and CD11b+ CD11c+ dendritic cells. CD11b+ Ly6G+ neutrophils only accumulated prominently at the late infection time point. Interestingly, parasite presence resulted in a significant reduction of B220+ IgM+ B cells, CD11b+ CD11clo/- SiglecF+ eosinophils and TcR-β- NK1.1+ natural killer cells. Digital transcriptomics revealed infection-induced upregulation of Il-10, IFN-ɣ- and IFN-α-responses, IL-2-, IL-6- and TNF-signalling, a Th1 pro-inflammatory signature, negative immune checkpoint regulators and a predominant M1 macrophage polarization. Il12a and genes associated with complement and the B cell receptor were downregulated. No infection-associated pulmonary dysfunction could be detected by in vivo lung function measurements, mirroring the limited pulmonary complications during sleeping sickness. However, the substantial reduction of eosinophils, B cells and NK cells may render individuals more susceptible to opportunistic infections. Collectively, these observations provide essential insights in the peculiar parasite biology, immunological reactions and physiological function of a largely overlooked target organ which may trigger new diagnostic approaches for sleeping sickness.

ORGANISM(S): Mus musculus Homo sapiens

PROVIDER: GSE212622 | GEO | 2022/10/25

REPOSITORIES: GEO

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Project description:The bloodstream forms of Trypanosoma brucei (BSF), responsible for the sleeping sickness, primarily evaluate in the blood of its mammalian hosts. The skin and the adipose tissues were recently identified as additional major sites for the parasite proliferation and transmission through its insect vector blood ingestion. Glucose is the only carbon source used by the blood parasites to feed its central metabolism, however, the metabolic behavior of the tissue-adapted parasites has not yet been addressed. Since production of glycerol is an important primary function of adipocytes, we have adapted the BSF trypanosomes to glucose-depleted and glycerol-rich growth medium (CMM_Gly/GlcNAc) and compared its metabolism and proteome with standard glucose-rich growth conditions (CMM_Glu). BSF consume 2-times more oxygen per carbon consumed in CMM_Gly/GlcNAc and is 11.5-times more sensitive to SHAM, a specific inhibitor of the alternative oxidase, which is consistent with the expected absolute requirement of the mitochondrial respiratory chain activity to convert glycerol into dihydroxyacetone phosphate. Metabolomic analyses by mass spectrometry showed that 13C-labeled glycerol is incorporated into hexose phosphates through gluconeogenesis. After several weeks of growth in CMM_Gly/GlcNAc, BSF adapt their metabolism by increasing and decreasing the rate of glycerol and glucose consumption, respectively. As expected RNAi-mediated down-regulation of glycerol kinase expression abolished glycerol degradation and is lethal for BSF growth in CMM_Gly/GlcNAc. However, the glycerol kinase activity is 7.8-fold decreased in CMM_Gly/GlcNAc, as confirms by western blotting and proteomic analyses, which suggests that the huge excess of glycerol kinase, which is not necessary for glycerol metabolism, is required for another yet undetermined non-essential function in glucose rich-conditions. Altogether these data shows that BSF trypanosomes are well adapted to glycerol-rich conditions, which could be encountered by the parasite in extravascular niches, such as skin and adipose tissues.

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Pulmonary parasite infection: do trypanosomes take your breath away?

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