title: Inflammation enhances myeloid-derived suppressor cell cross-talk by signaling through Toll-like receptor 4.
abstract: Myeloid-derived suppressor cells (MDSC) are potent inhibitors of anti-tumor immunity that facilitate tumor progression by blocking the activation of CD4(+) and CD8(+) T cells and by promoting a type 2 immune response through their production of IL-10 and down-regulation of macrophage production of IL-12. MDSC accumulate in many cancer patients and are a significant impediment to active cancer immunotherapies. Chronic inflammation has been shown recently to enhance the accumulation of MDSC and to increase their suppression of T cells. These findings led us to hypothesize that inflammation contributes to tumor progression through the induction of MDSC, which create a favorable environment for tumor growth. As chronic inflammation also drives type 2 immune responses, which favor tumor growth, we asked if inflammation mediates this effect through MDSC. We find that IL-1beta-induced inflammation increased IL-10 production by MDSC and induces MDSC, which are more effective at down-regulating macrophage production of IL-12 as compared with MDSC isolated from less-inflammatory tumor microenvironments, thereby skewing tumor immunity toward a type 2 response. Inflammation heightens MDSC phenotype by signaling through the TLR4 pathway and involves up-regulation of CD14. Although this pathway is well-recognized in other myeloid cells, it has not been implicated previously in MDSC function. These studies demonstrate that MDSC are an intermediary through which inflammation promotes type 2 immune responses, and they identify the TLR4 pathway in MDSC as a potential target for down-regulating immune suppression and promoting anti-tumor immunity.
authors.affiliation: University of Maryland Baltimore County, 1000 Hilltop Circle, Baltimore, MD 21250, USA.
authors.forename: Stephanie K
authors.initials: SK
authors.lastname: Bunt
authors.forename: Virginia K
authors.initials: VK
authors.lastname: Clements
authors.forename: Erica M
authors.initials: EM
authors.lastname: Hanson
authors.forename: Pratima
authors.initials: P
authors.lastname: Sinha
authors.forename: Suzanne
authors.initials: S
authors.lastname: Ostrand-Rosenberg
mesh_terms: D000818:Animals; D045744:Cell Line, Tumor; D015536:Down-Regulation / Q000187:drug effects; D007249:Inflammation / Q000276:immunology*; D016753:Interleukin-10 / Q000096:biosynthesis; D018664:Interleukin-12 / Q000096:biosynthesis; D053583:Interleukin-1beta; D018950:Lipopolysaccharide Receptors / Q000378:metabolism; D008070:Lipopolysaccharides / Q000494:pharmacology; D008262:Macrophage Activation / Q000187:drug effects; D008264:Macrophages / Q000166:cytology / Q000187:drug effects / Q000276:immunology; D051379:Mice; D008807:Mice, Inbred BALB C; D022423:Myeloid Cells / Q000187:drug effects / Q000276:immunology*; D020239:Receptor Cross-Talk; D015398:Signal Transduction / Q000187:drug effects; D051197:Toll-Like Receptor 4 / Q000378:metabolism*; D015854:Up-Regulation / Q000187:drug effects
chemical_list: D053583:Interleukin-1beta; D018950:Lipopolysaccharide Receptors; D008070:Lipopolysaccharides; C493487:Tlr4 protein, mouse; D051197:Toll-Like Receptor 4; D016753:Interleukin-10; D018664:Interleukin-12