Pathogen Evasion of Chemokine Response Through Suppression of CXCL10
Abstract
Clearance of intracellular pathogens, such as Leishmania (L.) major, depends on an immune response with well-regulated cytokine signaling. Here we describe a pathogen-mediated mechanism of evading CXCL10, a chemokine with diverse antimicrobial functions, including T cell recruitment. Infection with L. major in a human monocyte cell line induced robust CXCL10 transcription without increasing extracellular CXCL10 protein concentrations. We found that this transcriptionally independent suppression of CXCL10 is mediated by the virulence factor and protease, glycoprotein-63 (gp63). Specifically, GP63 cleaves CXCL10 after amino acid A81 at the base of a C-terminal alpha-helix. Cytokine cleavage by GP63 demonstrated specificity, as GP63 cleaved CXCL10 and its homologs, which all bind the CXCR3 receptor, but not distantly related chemokines, such as CXCL8 and CCL22. Further characterization demonstrated that CXCL10 cleavage activity by GP63 was produced by both extracellular promastigotes and intracellular amastigotes. Crucially, CXCL10 cleavage impaired T cell chemotaxis in vitro, indicating that cleaved CXCL10 cannot signal through CXCR3. Ultimately, we propose CXCL10 suppression is a convergent mechanism of immune evasion, as Salmonella enterica and Chlamydia trachomatis also suppress CXCL10. This commonality suggests that counteracting CXCL10 suppression may provide a generalizable therapeutic strategy against intracellular pathogens.
Importance
Leishmaniasis, an infectious disease that annually affects over one million people, is caused by intracellular parasites that have evolved to evade the host's attempts to eliminate the parasite. Cutaneous leishmaniasis results in disfiguring skin lesions if the host immune system does not appropriately respond to infection. A family of molecules called chemokines coordinate recruitment of the immune cells required to eliminate infection. Here, we demonstrate a novel mechanism that Leishmania (L.) spp. employ to suppress host chemokines: a Leishmania-encoded protease cleaves chemokines known to recruit T cells that fight off infection. We observe that other common human intracellular pathogens, including Chlamydia trachomatis and Salmonella enterica, reduce levels of the same chemokines, suggesting a strong selective pressure to avoid this component of the immune response. Our study provides new insights into how intracellular pathogens interact with the host immune response to enhance pathogen survival.
Acknowledgments
We thank Robyn Guo for assistance with immunoblotting, Sarah Rains for assistance with sample prep for CXCL10 cleavage site identification, and Jeffrey S. Bourgeois for thoughtful discussion about experimental design and analysis. For assistance with screening additional pathogens for CXCL10 cleavage we thank Emily Derbyshire, Maria Toro-Moreno, David Tobin, Ana-María Xet-Mull, Raphael Valdivia, Qin Yan, Vance Fowler, Jennifer Tenor, and John Perfect. We thank the Duke University School of Medicine for the use of the Proteomics and Metabolomics Shared Resource.
Footnotes
Funding. AA, KG, ET, KP, BS, and DK were supported by Duke Molecular Genetics and Microbiology startup funds, Duke University Whitehead Scholarship, Butler Pioneer Award, and NIH U19AI084044. ET was supported by the Duke Summer Research Opportunity Program (SROP). AM was supported by the Duke Department of Molecular Genetics and Microbiology Summer Undergraduate Research Experience (MGM SURE). JS and SR were supported by NIH {"type":"entrez-nucleotide","attrs":{"text":"GM122798","term_id":"221993598","term_text":"GM122798"}}GM122798 and the Burroughs Wellcome Fund Career Award for Medical Scientists. RR was supported by NIH {"type":"entrez-nucleotide","attrs":{"text":"AI119004","term_id":"3519328","term_text":"AI119004"}}AI119004.