Multiparameter analysis of immunogenetic mechanisms in clinical diagnosis and management of inflammatory bowel disease

Evolving paradigms in the pathogenesis of IBD

The pathogenesis of all immune-mediated inflammatory diseases has been carefully studied over the past several decades, but it is only recently that we have come to appreciate common pathways and genes. This is especially true for the inflammatory bowel diseases (IBD) Crohn's disease and ulcerative colitis, where a keener appreciation of the contributions of genetics, environment, and immune response have been dissected. In fact, in many ways, IBD has become the model for studying such disorders. The complex nature of interactions is continuing to be defined, and novel therapies targeting defects in these interactions have been developed and are being tested in the clinic. The era of bench to bedside has finally matured, and cures for debilitating diseases are now in sight. This review describes our current state of knowledge of each component of IBD pathogenesis. What has evolved is a clearer picture and novel targets for therapy.

Inflammatory bowel disease in Korea: epidemiological, genomic, clinical, and therapeutic characteristics

Inflammatory bowel disease (IBD) describes chronic inflammatory disease of the intestines and has a variable course; Crohn's disease and ulcerative colitis comprise the two main forms of the condition. Although IBD occurs worldwide, its epidemiologic and clinical characteristics vary depending upon the geographic location and the ethnicity of the population. Identifying the characteristic features of IBD in populations living in different geographical locations and with different ethnicities may provide significant clues about its etiology and pathophysiology, which in turn may be helpful in the development of more appropriate treatment strategies for IBD for these different populations. Therefore, it is important for each country and region to evaluate critically the epidemiology, genomics, and clinical characteristics of IBD among its own population. We have performed a critical review of the recent data in Korea, and describe herein the current epidemiologic and genotypic status, as well as the clinical manifestations and therapeutic responses of IBD that are unique to Korean patients.

Body traffic: ecology, genetics, and immunity in inflammatory bowel disease

The abundant bacteria and other microbial residents of the human intestine play important roles in nutrient absorption, energy metabolism, and defense against microbial pathogens. The mutually beneficial relationship of host and commensal microbiota represents an ancient and major coevolution in composition and mutual regulation of the human mucosa and the resident microbial community. Inflammatory bowel disease (IBD) is a set of chronic, relapsing inflammatory intestinal diseases in which rules of normal host-microbial interaction have been violated. This review considers the components of this host-microbial mutualism and the ways in which it is undermined by pathogenic microbial traits and by host immune and epithelial functions that confer to them susceptibility in patients with IBD. Recent advances in understanding the genetics of IBD and the immunology of host-microbial interaction are opening new strategies for treatments that target host susceptibility, candidate microbial pathogens, and intestinal ecology.

Bacteria and bacterial rRNA genes associated with the development of colitis in IL-10(-/-) mice

BACKGROUND

Microorganisms appear to play important yet ill-defined roles in the etiology of inflammatory bowel disease (IBD). This study utilized a novel population-based approach to identify bacteria and bacterial rRNA genes associated with the development of colitis in IL-10(-/-) mice.

METHODS

Mice were housed in 2 environments: a community mouse facility where the mice were fed nonsterile chow (Room 3) and a limited access facility where the mice were fed sterile chow (Room 4). Every month the disease activity levels were assessed and fecal bacterial compositions were analyzed. At the end of the experiments histological and bacterial analyses were performed on intestinal tissue.

RESULTS

Although disease activity increased over time in both environments, it progressed at a faster rate in Room 3 than Room 4. Culture and culture-independent bacterial analyses identified several isolates and phylotypes associated with colitis. Two phylotypes (GpC2 and Gp66) were distinguished by their negative associations with disease activity in fecal and tissue samples. Notably, rRNA genes from these phylotypes had high sequence identity (99%) to an rRNA gene from a previously described flagellated Clostridium (Lachnospiraceae bacterium A4).

CONCLUSIONS

The negative associations of these 2 phylotypes (GpC2 and Gp66) suggest that these bacteria were being immunologically targeted, consistent with prior findings that the Lachnospiraceae bacterium A4 bears a prevalent flagellar antigen for disease-associated immunity in murine immune colitis and human Crohn's disease. Identification of these associations suggests that the experimental approach used in this study will have considerable utility in elucidating the host-microbe interactions underlying IBD.

Diagnostics of inflammatory bowel disease

The diagnosis of inflammatory bowel disease (IBD) with its 2 main subforms, Crohn's disease and ulcerative colitis, is based on clinical, endoscopic, radiologic, and histologic criteria. This paradigm remains unchanged despite the advent of new molecular technologies for the examination of serum proteins and genetic sequences, respectively. The main innovations in diagnostic technologies include the development of more sophisticated endoscopic and noninvasive imaging techniques with the aim of improving the identification of complications, in particular malignant diseases associated with IBD. The future will see further progress in the identification of genetic susceptibility factors and of protein biomarkers and their use to describe the molecular epidemiology of IBD. It can be expected that future diagnostic algorithms will include molecular parameters to detect early disease or guide therapies by predicting the individual course of disease.

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.