Toxoplasma gondii is a common protozoan parasite that infects up to one third of the world’s population. Notably, very little is known about innate immune sensing mechanisms for this obligate intracellular parasite by human cells. Here, by applying an unbiased biochemical screening approach, we show that human monocytes recognized the presence of T. gondii infection by detecting the alarmin S100A11 protein, which is released from parasite-infected cells via caspase-1-dependent mechanisms. S100A11 induced a potent chemokine response to T. gondii by engaging its receptor RAGE, and regulated monocyte recruitment in vivo by inducing expression of the chemokine CCL2. Our experiments reveal a sensing system for T. gondii by human cells that is based on the detection of infection-mediated release of S100A11 and RAGE-dependent induction of CCL2, a crucial chemokine required for host resistance to the parasite.
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The materials, data, and any associated protocols that support the findings of this study are available from the authors upon reasonable request. All RNA-seq data generated in this study have been deposited in the Gene Expression Omnibus (GEO) under accession code GSE119835.
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This work was supported by National Institute of Allergy and Infectious Diseases grants R01AI136538 and R01AI121090 and by the Burroughs Wellcome Foundation.
The authors declare no competing interests.
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Integrated supplementary information
a, List of the most significant differentially expressed genes in human PBMCs infected with the Pru strain of T. gondii (MOI 3:1) for 12 h. b, Heat map of differentially expressed genes based on RNA-seq results of PBMCs infected with the RH strain of T. gondii (MOI 3:1) for 12 h.
a, Amino acid peptides detected by mass spectrometry. The red boxes denote the most frequently detected peptides by mass spectrometry. The data shown are representative of three independent experiments. b, Complete gel images from Figs. 4c and 5. Dotted markings indicate the parts used for the figures.
a–d, Knockdown of S100A11 in THP-1 cells was performed by siRNA targeting S100A11 or irrelevant targets (siRNA-GFP and ‘scrambled siRNA’). The efficiency of S100A11 knockdown was verified by immunoblot (a), qRT–PCR (b), and hS100A11-specific ELISA (c). THP-1 cells with the reduced S100A11 expression produced less CCL2 when infected with RH88 (c) or Pru (d) strains of T. gondii. The data shown (mean ± s.d.) are representative of three independent experiments. Each symbol represents an individual experimental sample.
Supplementary Figure 4 Gene ontology analysis identifies the RAGE pathway as activated in PBMCs infected by T. gondii (Pru strain).
Differentially expressed genes (fold change > 2, P < 0.001) in PBMCs (n = 5) identified by Ingenuity Pathway Analysis (IPA) software in response to the T. gondii Pru strain.
Supplementary Figure 5 Gene ontology analysis identifies the RAGE pathway as activated in PBMCs infected by T. gondii (RH88 strain).
Differentially expressed genes (fold change > 2, P < 0.001) in PBMCs (n = 5) identified by Ingenuity Pathway Analysis (IPA) software in response to T. gondii RH88 strain.
a, Parental (TATi) and inducible profilin knockout parasites (ΔPRFe/PRFi) were grown for 4 d ± anhydrotetracycline (ATc), harvested and incubated with THP-1 cells at a 3:1 ratio for 16 h in triplicates. CCL2 expression was then measured by RT–PCR. The experiment shown is representative of five independent experiments performed. b, MYB- (3 μM) or DMSO-pretreated T. gondii parasites were added to THP-1 cells (MOI 3:1) for 16 h, and CCL2 expression was analyzed by RT–PCR. Each symbol represents an individual experimental sample. The data shown represent the mean ± s.d.
a, A schematic diagram of the CRISPR/Cas9 strategy used to generate S100a11-deficient mice and primer design used in the study. Exons 2 and 3 of the S100a11 gene were targeted by two sgRNAs depicted as sg#9 and sg#3. b, Representative genotyping of the targeted alleles with a set of primers S100A11 wtF and S100A11 wtR that result in PCR products of 2.7 kb for WT mice and 557 bp for the S100a11 KO allele, as a result of deletion of exons 2 and 3.
a,b, WT and S100a11 KO mice (n = 5) were infected orally with T. gondii, and the presence of monocytes and neutrophils in small intestinal lamina propria (n = 3) was analyzed (a) and quantified by flow cytometry on day 7 after infection (b). c, CCL2 and IFN-γ secretion in small intestine. d, Parasite burden in small intestine (n = 5) was measured by qRT–PCR. e, Histological analysis of the small intestines (n = 5) of infected WT and S100a11 KO mice with 20 cysts of ME49 T. gondii on day 7 after infection. Image fields are representative of pathology in multiple tissue sections, and chosen sections were selected by blinded observation. f, Histological changes in the small intestine were analyzed on day 7 after infection based on an additive scoring system. The data shown (mean ± s.d.) are representative of three independent experiments. Each symbol represents an individual experimental sample, and unpaired two-tailed Student’s t test was used for statistical analysis; ns, not significant.
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Safronova, A., Araujo, A., Camanzo, E.T. et al. Alarmin S100A11 initiates a chemokine response to the human pathogen Toxoplasma gondii. Nat Immunol 20, 64–72 (2019). https://doi.org/10.1038/s41590-018-0250-8
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