Innate immune receptor genetic polymorphisms in pouchitis: is CARD15 a susceptibility factor?

Innate immunogenetics: a tool for exploring new frontiers of host defence

The discovery of innate immune genes, such as those encoding Toll-like receptors (TLRs), nucleotide-binding oligomerisation domain-like receptors (NLRs), and related signal-transducing molecules, has led to a substantial improvement of our understanding of innate immunity. Recent immunogenetic studies have associated polymorphisms of the genes encoding TLRs, NLRs, and key signal-transducing molecules, such as interleukin-1 receptor-associated kinase 4 (IRAK4), with increased susceptibility to, or outcome of, infectious diseases. With the availability of high-throughput genotyping techniques, it is becoming increasingly evident that analyses of genetic polymorphisms of innate immune genes will further improve our knowledge of the host antimicrobial defence response and help in identifying individuals who are at increased risk of life-threatening infections. This is likely to open new perspectives for the development of diagnostic, predictive, and preventive management strategies to combat infectious diseases.

Late-breaking news from the "4th International Meeting on Inflammatory Bowel Diseases" Capri, 2006

At the "4th International Meeting on Inflammatory Bowel Diseases: on the Way to New Therapies," Capri, 2006, genetics, bacteria-host interactions, immunomodulation, and tissue response were discussed deeply in order to understand, rationalize, and develop novel therapies. About genetics, the importance of a better understanding of the nature of known loci and of the putative associations was stressed. It was confirmed that genotype-phenotype associations in inflammatory bowel disease (IBD) have important clinical and therapeutic implications. The importance of the search for dominant bacterial antigens in chronic immune-mediated intestinal inflammation emerged, as well as knowledge of cellular and molecular mechanisms of bacterial-host interactions. It was discussed how innate and adaptive immunity signaling events can perpetuate chronic inflammation. Signal transduction pathways provide an intracellular mechanism by which cells respond and adapt to environmental stress. The identification of these signals have led to a greater understanding of the pathogenesis of IBD and pointed to potential therapeutic targets. It was shown that immune homeostasis is lost in IBD, resulting in a complex tissue response involving the action of immune and nonimmune cells. The nonimmune tissue response in IBD could be regarded as a new target for control of chronic intestinal inflammation. The changing role of biotherapy in IBD was widely discussed and in particular the anti-TNF-alpha monoclonal antibodies. Granulocyte-colony stimulating factor (GM-CSF) and stem cells therapies were also discussed. The risk-to-benefit ratio of the novel therapies was analyzed in detail. Finally, future directions for basic science and the unmet needs for clinical practice were presented.

Toll-like receptors and innate immunity in gut homeostasis and pathology

PURPOSE OF REVIEW

Immune responses to commensal bacteria and resulting chronic inflammation are hallmarks of inflammatory bowel disease. Considerable evidence has accumulated to suggest that innate immune defense mechanisms interact with pro-inflammatory pathways and exacerbate or perhaps even initiate development of inflammatory bowel disease.

RECENT FINDINGS

Recent cellular and mouse studies now show Toll-like receptor responses in intestinal epithelial cells are polarized and their activation by commensal bacteria plays an essential role in maintaining colonic homeostasis and controlling tolerance in the gut. Recent data also implicate signaling by Toll-like receptors and the common adaptor molecule MyD88 in intestinal epithelial homeostasis as well as the pathogenesis of inflammatory bowel disease, establishing a key link between the innate and adaptive immune defenses.

SUMMARY

We review recent progresses in the understanding of the role of Toll-like receptors and other pattern recognition receptors in the host defense against gastrointestinal pathogens and maintenance of immune tolerance to commensal bacteria, highlighting areas that should provide fertile ground for future studies aimed at a more comprehensive understanding of the interplay between innate and adaptive immune defense mechanisms and inflammatory bowel disease.

Risk factors for clinical phenotypes of Crohn's disease of the ileal pouch

BACKGROUND

Crohn's disease (CD) of the pouch can occur in patients with colectomy and ileal pouch-anal anastomosis (IPAA) originally performed for a preoperative diagnosis of ulcerative colitis. The clinical presentations of CD of the pouch are inflammatory, fibrostenotic, and fistulizing. Risk factors for clinical phenotypes of CD of the pouch have not been characterized.

METHODS

A total of 78 eligible patients with CD of the pouch together with 294 nonselected non-CD patients with IPAA seen in the Pouchitis Clinic were enrolled, including 28 with inflammatory CD, 18 with fibrostenotic CD, and 32 with fistulizing CD. The clinical phenotypes of CD were diagnosed based on a combined assessment of clinical, endoscopic, radiographic, and histologic features. Three separate analyses were performed, and for each analysis, the outcome of interest was having one of the phenotypes versus not having it. A stepwise selection multivariable logistic regression analysis was used.

RESULTS

In the multivariable analysis, the risk factor for inflammatory CD was higher afferent-limb endoscopy scores (hazard ratio [HR] 1.87 95% confidence interval [CI] 1.54-2.27); the risk factors for fibrostenotic CD were higher afferent-limb (95% CI 1.81-3.48, HR 2.51) and higher cuff (95% CI 1.01-1.84, HR 1.36) endoscopy scores; and for fistulizing CD the risk factors were younger age (95% CI 0.93-0.99, HR 0.96), female gender (95% CI 1.35-6.97, HR 3.07), a preoperative diagnosis of indeterminate colitis (95% CI 1.72-9.34, HR 4.00), and no use of nonsteroidal antiinflammatory drugs (95% CI 1.31-8.25, HR 3.28).

CONCLUSIONS

Each of the three phenotypes of CD of the pouch was associated with certain risk factors, suggesting that each of these diseases has a different etiology and disease process. The identification and management of some of the modifiable risk factors may reduce CD-related morbidity.

CARD15/NOD2 mutations in Crohn's disease

Inflammatory bowel diseases (IBDs) are complex genetic disorders characterized by a complex interplay between genetic and environmental risk factors. At least ten genes or anonymous loci have been proposed to play a role in IBD. Among them, the best studied is CARD15/NOD2, a gene coding for a protein involved in bacterial recognition by cells involved in innate immunity. Despite a large amount of work, a consensus model explaining the effect of Card 15/NoD2 mutations did not emerge, and the disease mechanisms are still subject to debate.