Because overgrowth of gram-negative bacteria is commonly observed in the inflamed intestine (14, 37) and LPS is believed to be one of the causes of NEC (18), our study suggests important evidence to determine the effect of colonic LPS in the development and progress of intestinal ref 1 inflammatory diseases. GRANTS This work was supported by a Young Clinical Scientist Award from the Flight Attendant Medical Research Institute (S. H. Rhee and E. Im), Pusan National University Research Grant, 2012 (E. Im.), and National Institute of Diabetes and Digestive and Kidney Diseases Grants DK-072471 (C. Pothoulakis), DK-083336 (E. Im), and DK-079015 (S. H. Rhee). DISCLOSURES No conflicts of interest, financial or otherwise, are declared by the authors. AUTHOR CONTRIBUTIONS E.I. and S.H.R.

are responsible for conception and design of the research; E.I., F.M.R., and S.H.R. performed the experiments; E.I. and S.H.R. analyzed the data; E.I. and S.H.R. interpreted the results of the experiments; E.I., F.M.R., and S.H.R. drafted the manuscript; E.I., C.P., and S.H.R. edited and revised the manuscript; E.I., F.M.R., C.P., and S.H.R. approved the final version of the manuscript; S.H.R. prepared the figures.
The gastrointestinal tract is lined with a single layer of epithelial cells that separates the gut lumen from the connective tissue and the immune system (Kaser et al., 2010; MacDonald et al., 2011). Because it is constantly exposed to dietary and environmental antigens and to an estimated community of 1014 commensal bacteria, the immune system is confronted with the difficult task of enforcing tolerance to innocuous environmental antigens while also protecting against invading pathogens.

An aberrant immune response to the intestinal microbiota contributes to the pathogenesis of Crohn��s disease (CD), a chronic inflammatory bowel disease (IBD) that affects genetically predisposed individuals (Chassaing and Darfeuille-Michaud, 2011; Maloy and Powrie, 2011). Mononuclear phagocytes, which include a large population Dacomitinib of macrophages (M��) and rare subsets of DCs, are critical for the establishment and maintenance of gut homeostasis (Coombes and Powrie, 2008; Varol et al., 2010). However, myeloid cell heterogeneity in phenotype, origin, and function has led to confusion over the classification between M�� and DCs, especially in mucosal tissues (Gautier et al., 2012; Miller et al., 2012). In murine tissues, CD11c is not an adequate marker to identify DCs because it is also expressed in varying levels on F4/80+ M�� (Medina-Contreras et al., 2011; Rivollier et al., 2012). This is in contrast to resident M�� in human lamina propria (LP), which do not express CD11c (Smith et al., 2011).