Thus, in a model of infectious colitis induced by Citrobacter rodentium in IL-1R or MyD88 KO mice, an exacerbated form of disease was observed in the KO mice, indicating that IL-1R signaling is essential for colon repair and resolution of colitis [143]. To directly assess the role of the IL-1 molecules in colon inflammation, we induced colitis in IL-1 KO mice, lacking either IL-1 or IL-1, and examined their patterns of acute DSS-induced colitis [144]. in the unique microenvironment in the colon is largely unknown. Here, we described the role of IL-1 and IL-1 in colon homeostasis, colon inflammation, colon carcinogenesis and invasiveness of colorectal cancer. Understanding of the integrative role of IL-1 and IL-1 in these processes will facilitate the application of novel IL-1 modulating approaches. Keywords: IL-1, IBD, CRC, Carcinogenesis, Inflammation, Tumor invasiveness == Instruction == Colon cancer is one of the most common malignancies observed in clinical practice. More than 1 . 2 million cases of colorectal cancer (CRC) are diagnosed each year worldwide. CRC remains the fourth most common cause of cancer-related death in NS13001 western countries, in spite of early screening and improved treatment, including advances in surgery, chemotherapy and biological therapy [reviewed in [1]]. Survival of CRC patients is highly dependent on the tumor stage at the time of diagnosis. Over one-third of patients die within five years of the initial diagnosis, mainly from liver metastasis [reviewed in [1]]. NS13001 Colon carcinogenesis is a multistep process, in which normal colon epithelial cells (IECs) are transformed to malignant cells. Approximately 20 % of CRC cases have a familial background, however , the majority have been linked to environmental causes rather than heritable genetic changes. Environmental risk factors for CRC include food-borne mutagens, specific intestinal commensals and chronic intestinal inflammation [reviewed in [2]]. Fifteen percent of all epithelial tumors develop in organs in which chronic inflammation occurs. As in all solid tumors, the microenvironment of colon tumors consist of recruited inflammatory cells from the bone marrow (BM) and stromal cells. In most instances, the microenvironment supports invasiveness and tumor progression [(reviewed in [35]]. Correlation between prolonged inflammation and susceptibility to CRC is documented in patients with chronic inflammatory bowel disease (IBD), such as SEMA3F ulcerative colitis (UC) and Crohns disease (CD) [reviewed in [311]]. Patients suffering from UC for more than 35 years show an increased risk for CRC development from 18 to 35 %, while 8 % of CD patients are at risk of carcinogenesis [reviewed in [12, 13]]. The CRC subtype that is associated with IBD is difficult to treat and has a high mortality rate. == The Microenvironment of the Colon == Intestinal mononuclear phagocytes, which normally reside in the intestinal lamina propria (LP), such as macrophages and DCs, are important in preventing harmful responses to food constituents and commensal bacteria [14]. However , in the presence of pathogenic bacteria, the immune system can elicit robust inflammatory and protective host-defensive responses in the intestine [1517]. A central question is how the immune system discriminates between commensal NS13001 and pathogenic bacteria. This issue is particularly important in the intestine, where a large number of commensal microorganisms challenge the immune system without eliciting pro-inflammatory responses [18]. The signals that program mononuclear phagocytes to become anergic to Toll NS13001 like receptor (TLR) ligands of commensals and thus maintain intestinal homeostasis have not yet been elucidated. Induction of anti-inflammatory cytokines following the engulfment and degradation of commensal bacteria in intestinal macrophages are among the possible mechanisms conferring tolerance. For example , mononuclear phagocytes of the LP do not produce TNF and IL-6 when stimulated with TLR ligands or commensal bacteria [19, 20]. Another possible mechanism for tolerance is the low expression of TLRs or key components of patterns recognition receptors (PRRs) signaling in intestinal mononuclear cells [21]. Production of IL-10 by mononuclear cells and TGF by stromal cells were also shown to be involved in suppression of colon immunity to commensals [20, 22]. IL-10 is secreted by Treg cells, which are abundant in the intestine and play a significant role in colon homeostasis. Treg cells also suppress the induction and function of effector T cells, especially pro-inflammatory Th17, and inhibit the activation/function of mononuclear cells. Given that resident macrophages and dendritic cells are anergic to TLR ligands and commensal bacteria, it is unclear if they can actively promote host defenses against pathogenic bacteria. Alternatively, infiltrating myeloid cells, such as neutrophils, myeloid derived suppressor cells (MDSCs), inflammatory monocytes and macrophages differentiated from them could be responsible for eliminating pathogenic bacteria. Major pathological features of colon chronic inflammation, such as IBD, include intestinal epithelial cells (IEC) injury and disruption of.