OBJECTIVE: Plasma levels of high-density lipoprotein (HDL) cholesterol are frequently found decreased in patients with inflammatory bowel disease (IBD). Therefore, and because HDL exerts anti-inflammatory activities, we investigated whether HDL and its major protein component apolipoprotein A-I (apoA-I) modulate mucosal inflammatory responses in vitro and in vivo.
METHODS: The human intestinal epithelial cell line T84 was used as the in vitro model for measuring the effects of HDL on the expression and secretion of tumor necrosis factor (TNF), interleukin-8 (IL-8), and intracellular adhesion molecule (ICAM). Nuclear factor-κB (NF-κB)-responsive promoter activity was studied by dual luciferase reporter assays. Mucosal damage from colitis induced by dextran sodium sulphate (DSS) and 2,4,6-trinitrobenzenesulfonic acid (TNBS) was scored by colonoscopy and histology in apoA-I transgenic (Tg) and apoA-I knockout (KO) and wild-type (WT) mice. Myeloperoxidase (MPO) activity and TNF and ICAM expression were determined in intestinal tissue samples. Autophagy was studied by Western blot analysis, immunofluorescence, and electron microscopy.
RESULTS: HDL and apoA-I down-regulated TNF-induced mRNA expression of TNF, IL-8, and ICAM, as well as TNF-induced NF-κB-responsive promoter activity. DSS/TNBS-treated apoA-I KO mice displayed increased mucosal damage upon both colonoscopy and histology, increased intestinal MPO activity and mRNA expression of TNF and ICAM as compared with WT and apoA-I Tg mice. In contrast, apoA-I Tg mice showed less severe symptoms monitored by colonoscopy and MPO activity in both the DSS and TNBS colitis models. In addition, HDL induced autophagy, leading to recruitment of phosphorylated IκB kinase to the autophagosome compartment, thereby preventing NF-κB activation and induction of cytokine expression.
CONCLUSIONS: Taken together, the in vitro and in vivo findings suggest that HDL and apoA-I suppress intestinal inflammation via autophagy and are potential therapeutic targets for the treatment of IBD.

OBJECTIVE: Granulocyte macrophage colony-stimulating factor (GM-CSF) treatment induces clinical response in patients with active Crohn\'s disease. To explore whether monocytes mediate GM-CSF effects in vivo, we used a mouse model of chronic colitis induced by dextran sulfate sodium (DSS).
METHODS: Murine bone marrow-derived monocytes were activated with GM-CSF in vitro, and gene expression, phenotype, and function of GM-CSF-activated monocytes (GMaM) were analyzed. Therapeutic effects of GMaM were assessed in a model of chronic colitis induced by repeated cycles of DSS. Monocytes were administered intravenously and their immunomodulatory functions were evaluated in vivo by clinical monitoring, histology, endoscopy, immunohistochemistry, and expression of inflammatory markers in the colon. The distribution of injected monocytes in the intestine was measured by in vivo imaging.
RESULTS: GMaM expressed significantly higher levels of anti-inflammatory molecules. Production of reactive oxygen species was also increased while phagocytosis and adherence were decreased. GMaM up-regulated CD39 and CD73, which allows the conversion of adenosine triphosphate into adenosine and coincided with the induction of Foxp3+ (forkhead-box-protein P3 positive) regulatory T cells (Treg) in cocultures of GMaM and naive T cells. In chronic DSS-induced colitis, adoptive transfer of GMaM led to significant clinical improvement, as demonstrated by reduced weight loss, inflammatory infiltration, ulceration, and colon shrinkage. As GMaM migrated faster and persisted longer in the inflamed intestine compared with control monocytes, their presence induced Treg generation in vivo.
CONCLUSIONS: GM-CSF leads to specific monocyte activation that modulates experimental colitis via mechanisms that include the induction of Treg. We demonstrate a possible mechanism of Treg induction through CD39 and CD73 expression on monocytes.