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The mouse pathogen Citrobacter rodentium is utilized as a model organism for studying infections caused by the human pathogens enteropathogenic Escherichia coli (EPEC) and enterohemorrhagic E. coli (EHEC) and to elucidate mechanisms of mucosal immunity. In response to C. rodentium infection, innate lymphoid cells and T cells secrete interleukin (IL)-22, a cytokine that promotes mucosal barrier function. IL-22 plays a pivotal role in enabling mice to survive and recover from C. rodentium infection, although the exact mechanisms involved remain incompletely understood. Here, we investigated whether particular components of the host response downstream of IL-22 contribute to the cytokine's protective effects during C. rodentium infection. In line with previous research, mice lacking the IL-22 gene (Il22-/- mice) were highly susceptible to C. rodentium infection. To elucidate the role of specific antimicrobial proteins modulated by IL-22, we infected the following knockout mice: S100A9-/- (calprotectin), Lcn2-/- (lipocalin-2), Reg3b-/- (Reg3β), Reg3g-/- (Reg3γ), and C3-/- (C3). All knockout mice tested displayed a considerable level of resistance to C. rodentium infection, and none phenocopied the lethality observed in Il22-/- mice. By investigating another arm of the IL-22 response, we observed that C. rodentium-infected Il22-/- mice exhibited an overall decrease in gene expression related to intestinal barrier integrity as well as significantly elevated colonic inflammation, gut permeability, and pathogen levels in the spleen. Taken together, these results indicate that host resistance to lethal C. rodentium infection may depend on multiple antimicrobial responses acting in concert, or that other IL-22-regulated processes, such as tissue repair and maintenance of epithelial integrity, play crucial roles in host defense to attaching and effacing pathogens.

There is strong evidence that exposure to fine particulate matter (PM2.5) and a high-fat diet (HFD) increase the risk of mortality from atherosclerotic cardiovascular diseases. Recent studies indicate that PM2.5 generated by combustion activates the Aryl Hydrocarbon Receptor (AHR) and inflammatory cytokines contributing to PM2.5-mediated atherogenesis. Here we investigate the effects of components of a HFD on PM-mediated activation of AHR in macrophages. Cells were treated with components of a HFD and AHR-activating PM and the expression of biomarkers of vascular inflammation was analyzed. The results show that glucose and triglyceride increase AHR-activity and PM2.5-mediated induction of cytochrome P450 (CYP)1A1 mRNA in macrophages. Cholesterol, fructose, and palmitic acid increased the PM- and AHR-mediated induction of proinflammatory cytokines in macrophages. Treatment with palmitic acid significantly increased the expression of inflammatory cytokines and markers of vascular injury in human aortic endothelial cells (HAEC) after treatment with PM2.5. The PM2.5-mediated activation of the atherogenic markers C-reactive protein (CRP) and S100A9, a damage-associated molecular pattern molecule, was found to be AHR-dependent and involved protein kinase A (PKA) and a CCAAT/enhancer-binding protein (C/EBP) binding element. This study identified nutritional factors interacting with AHR signaling and contributing to PM2.5-induced markers of atherogenesis and future cardiovascular risk.

BackgroundNeutrophil expression of the Fcγ receptor I (CD64) is upregulated in adult patients with clinically active inflammatory bowel disease (IBD). We tested the relationship of CD64 with mucosal inflammation and clinical relapse in pediatric Crohn's disease (CD).MethodsIn a cohort of 208 newly diagnosed CD and 43 non-IBD controls, ileal expression of FcγRI/S100A9 was determined by RNA sequencing from biopsies obtained at ileocolonoscopy. In a second cohort, we tested for the peripheral blood polymorphonuclear neutrophil (PMN) CD64 index from 26 newly diagnosed CD, 30 non-IBD controls, and 83 children with established CD.ResultsIleal FcγRIA mRNA expression was significantly elevated in CD at diagnosis compared with non-IBD controls (P < 0.001), and correlated with ileal S100A9 (calprotectin) expression (r = 0.83, P < 0.001). The median (range) PMN CD64 index for newly diagnosed CD was 2.3 (0.74-9.3) compared with 0.76 (0.39-1.2) for non-IBD controls (P < 0.001) with 96% sensitivity and 90% specificity at the cut point of 1.0. The PMN CD64 index significantly correlated with mucosal injury as measured by the simple endoscopic score for CD (r = 0.62, P < 0.001). Patients with CD in clinical remission receiving maintenance therapy with a PMN CD64 index 1.0 (P < 0.01).ConclusionsAn elevated PMN CD64 index is associated with both mucosal inflammation and an increased risk for clinical relapse in pediatric CD. The PMN CD64 index is a reliable marker for sustained remission in patients with CD receiving maintenance therapy.

BackgroundAs therapies for systemic cancer improve and patients survive longer, the risk for brain metastases increases. We evaluated whether immune mechanisms are involved in the development of brain metastasis.MethodsWe conducted our studies using BALB/c mice bearing syngeneic 4T1 mammary adenocarcinoma cells in the mammary gland.ResultsThe brains of mice bearing 4T1 tumors at day 14 had no detectable metastatic tumor cells but presented with marked accumulation of bone marrow-derived CD11b(+)Gr1(+) myeloid cells, which express high levels of inflammatory chemokines S100A8 and S100A9. In vitro, S100A9 attracts 4T1 cells through Toll-like receptor 4 and CD11b(+)Gr1(+) myeloid cells through Toll-like receptor 4 and the receptor for advanced glycation end-products. Systemic treatment of 4T1-bearing mice with anti-Gr1 (RB6-8C5) monoclonal antibody reduces accumulation of CD11b(+)Gr1(+) myeloid cells in the day-14 premetastatic brain as well as subsequent brain metastasis of 4T1 cells detected on day 30. Furthermore, treatment of 4T1 tumor-bearing mice with the cyclooxygenase-2 inhibitor celecoxib or genetic disruption of cyclooxygenase-2 in 4T1 cells inhibits the inflammatory chemokines and infiltration of CD11b(+)Gr1(+) myeloid cells in the premetastatic brain and subsequent formation of brain metastasis.ConclusionsOur results suggest that the primary tumor induces accumulation of CD11b(+)Gr1(+) myeloid cells in the brain to form "premetastatic soil" and inflammation mediators, such as S100A9, that attract additional myeloid cells as well as metastatic tumor cells. Celecoxib and anti-Gr1 treatment may be useful for blockade of these processes, thereby preventing brain metastasis in patients with breast cancer.