Mutation scan of a type 1 diabetes candidate gene: the human interleukin-18 binding protein gene

IL-18 in inflammatory and autoimmune disease

Inflammation serves as the first line of defense in response to tissue injury, guiding the immune system to ensure preservation of the host. The inflammatory response can be divided into a quick initial phase mediated mainly by innate immune cells including neutrophils and macrophages, followed by a late phase that is dominated by lymphocytes. Early in the new millennium, a key component of the inflammatory reaction was discovered with the identification of a number of cytosolic sensor proteins (Nod-like receptors) that assembled into a common structure, the 'inflammasome'. This structure includes an enzyme, caspase-1, which upon activation cleaves pro-forms of cytokines leading to subsequent release of active IL-1 and IL-18. This review focuses on the role of IL-18 in inflammatory responses with emphasis on autoimmune diseases.

Genetic and Molecular Basis of QTL of Diabetes in Mouse: Genes and Polymorphisms

A systematic study has been conducted of all available reports in PubMed and OMIM (Online Mendelian Inheritance in Man) to examine the genetic and molecular basis of quantitative genetic loci (QTL) of diabetes with the main focus on genes and polymorphisms. The major question is, What can the QTL tell us? Specifically, we want to know whether those genome regions differ from other regions in terms of genes relevant to diabetes. Which genes are within those QTL regions, and, among them, which genes have already been linked to diabetes? whether more polymorphisms have been associated with diabetes in the QTL regions than in the non-QTL regions.

Our search revealed a total of 9038 genes from 26 type 1 diabetes QTL, which cover 667,096,006 bp of the mouse genomic sequence. On one hand, a large number of candidate genes are in each of these QTL; on the other hand, we found that some obvious candidate genes of QTL have not yet been investigated. Thus, the comprehensive search of candidate genes for known QTL may provide unexpected benefit for identifying QTL genes for diabetes.

Association of polymorphisms in the interleukin-18 gene in patients with Crohn's disease depending on the CARD15/NOD2 genotype

An increased expression of interleukin-18 (IL-18), a proinflammatory cytokine inducing interferon-gamma, has been found in Crohn's disease (CD). In the IL-18 gene, several partly functional relevant polymorphisms are known. This study sought to investigate associations of IL-18 polymorphisms in inflammatory bowel disease and CD according to CARD15/NOD2 mutation status and clinical phenotypes.

METHODS

The IL-18 polymorphisms -607, -137, and the third position of codon 35 (c35/3) were genotyped in 210 patients with CD, 140 patients with ulcerative colitis, and 265 healthy controls using polymerase chain reaction and restriction fragment length polymorphism analysis.

RESULTS

Frequencies of alleles and genotypes of the 3 polymorphisms and of the respective haplotypes and diplotypes displayed no significant differences between the whole groups of patients with CD and ulcerative colitis, respectively, compared with the controls. After stratification of patients with CD for CARD15/NOD2 status, significant associations of genotypes -137 CC (P = 0.018) and c35/3 CC (P = 0.010) and of the diplotype 2-2 (P = 0.018) were found in cases carrying CARD15/NOD2 mutations. Associations of genotypes -137 GG (P = 0.015) and c35/3 AA (P = 0.030) with colonic disease only in cases positive for CARD15/NOD2 mutations and of the genotype -607 AA (P = 0.007) with fistulas in cases negative for CARD15/NOD2 mutations were observed.

CONCLUSIONS

In this study, significant differences of several genotypes and diplotypes within the IL-18 gene in CD depending on CARD15/NOD2 status have been found. In context with an increased expression of IL-18 in CD, it remains to be shown whether the expression of IL-18 is influenced by CARD15/NOD2 mutation status.

Interleukin-18: recent advances

PURPOSE OF REVIEW

Interleukin-18 (IL-18) has potent immunomodulatory effects. It is the only cytokine with a unique capacity to induce T helper 1 or T helper 2 polarization, depending on the immunologic context. Serum levels of IL-18 are increased in many human diseases and it has been implicated in the pathogenesis of several immune-mediated processes. Some of the recent key advances in the immunobiology of IL-18 are discussed in this review.

RECENT FINDINGS

Recent data from several laboratories have shed light on the structure of IL-18; the signaling cascades that are initiated; and its role on modulating T cells, dendritic cells, and natural killer cell function. Several new reports have expanded and delineated the role of IL-18 in a multitude of diseases, but only recent advances in the role of IL-18 in three disease processes (acute graft-versus-host disease, insulin-dependent diabetes, and sepsis), where it appears to play paradoxic roles are discussed.

SUMMARY

Although emerging data shed more light on the complex role of IL-18 in immune reactions, they also pose more questions. Given the pleiotropic, complex, and at times paradoxic effects of IL-18 in various disease processes, better understanding of its immunobiology might lead to the development of IL-18 and/or its antagonists as therapeutic agents against immune-mediated diseases.