The understanding of the intestinal inflammation occurring in the inflammatory bowel diseases (IBD) has been immeasurably advanced by the development of the now numerous murine models of intestinal inflammation. The usefulness of this research tool in IBD studies has been enabled by our improved knowledge of mucosal immunity and thus our improved ability to interpret the complex responses of mice with various causes of colitis; in addition, it has been powered by the availability of models in which the mice have specific genetic and/or immunologic defects that can be related to the origin of the inflammation. Finally, and more recently, it has been enhanced by our newly acquired ability to define the intestinal microbiome under various conditions and thus to understand how intestinal microorganisms impact on inflammation. In this brief review of murine models of intestinal inflammation we focus mainly on the most often used models that are, not incidentally, also the models that have yielded major insights into IBD pathogenesis.

IL-13 is a central mediator of allergic inflammation. The single nucleotide polymorphism IL13-1112C>T (rs1800925) is associated with allergic phenotypes in ethnically distinct populations, but the underlying mechanism(s) remain unknown. Using in vivo, in vitro, and in silico analysis, we show that the IL13-1112T allele enhanced IL13 promoter activity in primary human and murine CD4+ Th2 lymphocytes. Increased expression of IL13-1112T in Th2 cells was associated with the creation of a Yin-Yang 1 binding site that overlapped a STAT motif involved in negative regulation of IL13 expression and attenuated STAT6-mediated transcriptional repression. Because IL-13 secretion was increased in IL13-1112TT homozygotes, we propose that increased expression of IL13-1112T in vivo may underlie its association with susceptibility to allergic inflammation. Interestingly, IL13-1112T had opposite transcriptional effects in nonpolarized CD4+ T cells, paralleled by distinct patterns of DNA-protein interactions at the IL13 promoter. Our findings suggest the nuclear milieu dictates the functional outcome of genetic variation.

Natural killer (NK) cells help protect the host against viral infections and tumors. NKG2D is a vital activating receptor, also expressed on subsets of T cells, whose ligands are up-regulated by cells in stress. Ligation of NKG2D leads to phosphorylation of the associated DAP10 adaptor protein, thereby activating immune cells. Understanding how the expression of NKG2D-DAP10 is regulated has implications for immunotherapy. We show that IL-2 and TGF-β1 oppositely regulate NKG2D-DAP10 expression by NK cells. IL-2 stimulation increases NKG2D surface expression despite a decrease in NKG2D mRNA levels. Stimulation with IL-2 results in a small increase of DAP10 mRNA and a large up-regulation of DAP10 protein synthesis, indicating that IL-2-mediated effects are mostly posttranscriptional. Newly synthesized DAP10 undergoes glycosylation that is required for DAP10 association with NKG2D and stabilization of NKG2D expression. TGF-β1 has an opposite and dominant effect to IL-2. TGF-β1 treatment decreases DAP10, as its presence inhibits the association of RNA polymerase II with the DAP10 promoter, but not NKG2D mRNA levels. This leads to the down-regulation of DAP10 expression and, as a consequence, NKG2D protein as well. Finally, we show that other γ(c) cytokines act similarly to IL-2 in up-regulating DAP10 expression and NKG2D-DAP10 surface expression.

Expression of the cytokine interleukin-13 (IL13) is critical forThe T cell-derived cytokine interleukin (IL) 2 -13 plays a pivotal effector role in T helper type 2 (Th2) immune responses to extracellular parasites (1). When dysregulated by genetic and/or environmental factors, IL13 expression is essential for the pathogenesis of allergic diseases (2). Indeed, experimental animal models have shown that IL-13 is necessary and sufficient to induce all the cardinal features of allergic lung inflammation, including airway hyper-responsiveness, eosinophilia, goblet cell metaplasia and mucus hyper-secretion, epithelial cell damage, and fibrosis (3-5). IL13 expression and IL-13-dependent events are also amplified in human allergy (6, 7), and high IL-13 production in early life is strongly associated with the subsequent development of allergic sensitization (8 -10).The IL13 gene lies within the Th2 cytokine locus on human chromosome 5q31, which also includes IL4 and IL5. Th2 cytokine gene expression has been shown to be tightly coordinated and fine-tuned by multiple local and distant cis-regulatory elements that are located throughout the Th2 locus and are marked by developmentally conserved DNase I-hypersensitive (HS) sites (11). HS sites typically reflect the DNA binding activity of sequence-specific trans-acting factors that induce destabilization or displacement of local nucleosomes (12) and mark the location of enhancers, silencers, or locus control regions (13). In the murine Th2 locus, nuclease HS regions appear to work cooperatively (14, 15) and engage in local and long range intra-chromosomal interactions that are essential for concerted Th2 cytokine expression (16).We recently characterized the dynamic modifications in DNase I hypersensitivity and epigenetic marks that occur at the human IL13 locus during the differentiation of naive CD4ϩ Th cells into a polarized IL-13/IL-4 secreting Th2 phenotype (17). Our study demonstrated that distinct regions of the IL13 locus exhibit distinct patterns of chromatin accessibility at defined stages of the Th cell differentiation process. In naive T cells, chromatin at the proximal promoter, the transcription unit, and the IL13/IL4 intergenic region was in an inaccessible state, marked by the absence of HS sites and by extensive CpG hypermethylation. During Th2 differentiation, these regions underwent profound remodeling, revealed by the appearance of numerous HS sites that co-localized with DNA hypomethylation. In contrast, the distal IL13 promoter contained two closely spaced, novel HS sites, HS4 and HS5, which were detectable in unstimulated naive CD4 ϩ T cells and persisted throughout Th cell differentiation (17). Detection of constitutive HS sites in naive CD4ϩ T cells was intriguing because these cells rapidly express substantial amounts of IL-13 upon T cell receptor cross-linking (18). Early accessibility of the distal promoter suggested occupancy of HS4 and HS5 by constitutive transcription * This work was supported, in whole or in part, by National Institutes of Hea...

IL-13 is a central effector of Th2-mediated allergic inflammation and is critical for the induction of IgE synthesis. Common IL13 variants are associated with allergy phenotypes in populations of distinct ethnic background. We recently demonstrated that IL13 expression by human CD4+ T cells is paralleled by extensive IL13 locus remodeling, which results in the appearance of multiple DNase I hypersensitive sites. Among these, HS4 in the distal promoter is constitutive in both naïve and polarized Th1 and Th2 cells, and spans a common single nucleotide polymorphism, IL13-1512A>C (rs1881457), strongly associated with total serum IgE levels. We recently characterized HS4 as a novel cis-acting element that upregulates IL13 transcription in activated human and murine T cells. Here we show that IL13-1512A>C is a functional polymorphism that significantly enhances HS4-dependent IL13 expression by creating a binding site for the transcription factor Oct-1. Of note, endogenous Oct-1 was preferentially recruited to the IL13-1512C risk allele in primary CD4+ T cells from IL13-1512A>C heterozygous subjects. Moreover, the IL13-1512C allele was overexpressed in transfected Th2 cells from Oct1(+/+) mice, but not from Oct1(+/-) mice, demonstrating that increased activity was exquisitely dependent on physiologic levels of Oct-1. Our results illustrate how a functional variant in a regulatory element enhances transcription of an allergy-associated gene, thereby modulating disease susceptibility.

Acute graft-versus-host disease (aGVHD) is an immune-mediated reaction that can occur after hematopoietic stem cell transplantation in which donor T cells recognize the host antigens as foreign, destroying host tissues. Establishment of a tolerogenic immune environment while preserving the immune response to infectious agents is required for successful bone marrow transplantation. Pregnancy-specific glycoprotein 1 (PSG1), which is secreted by the human placenta into the maternal circulation throughout pregnancy, likely plays a role in maintaining immunotolerance to prevent rejection of the fetus by the maternal immune system. We have previously shown that PSG1 activates the latent form of transforming growth factor b1 (TGF-b), a cytokine essential for the differentiation of tolerance-inducing CD4 + FoxP3 + regulatory T cells (Tregs). Consistent with this observation, treatment of na€ ıve murine T cells with PSG1 resulted in a significant increase in FoxP3 + cells that was blocked by a TGF-b receptor I inhibitor. We also show here that PSG1 can increase the availability of active TGF-b in vivo. As the role of CD4 + FoxP3 + cells in the prevention of aGVHD is well established, we tested whether PSG1 has beneficial effects in a murine aGHVD transplantation model. PSG1-treated mice had reduced numbers of tissueinfiltrating inflammatory CD3 + T cells and had increased expression of FoxP3 in T cells compared with vehicletreated mice. In addition, administration of PSG1 significantly inhibited aGVHD-associated weight loss and mortality. On the other hand, administration of PSG1 was less effective in managing aGVHD in the presence of an alloimmune reaction against a malignancy in a graft-versus-leukemia experimental model. Combined, this data strongly suggests that PSG1 could be a promising treatment option for patients with aGVHD following bone marrow transplantation for a nonmalignant condition, such as an autoimmune disorder or a genetic immunodeficiency. Published by Elsevier Inc. on behalf of American Society for Blood and Marrow Transplantation.

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Dysregulated production of the Th2 cytokines IL4 and IL13 is a hallmark of allergy and asthma. Th2 cytokine gene locus regulation has been extensively studied in mice, much less in humans. We have generated mice carrying a 160 kb BAC transgene (BAC5) that encompasses human RAD50, IL13 and IL4 and includes all the elements known to be required for faithful regulation of mouse Th2 cytokine locus. BAC5 transgenic mice appeared normal, were born at the expected Mendelian ratio, and carried 1-15 intact copies of BAC5. In vitro polarized mouse transgenic CD4 Th2, but not Th1 cells expressed human IL13 and IL4, demonstrating tissue-specific regulation of human Th2 cytokines. Murine CD4 T cells expressed physiologic levels of human IL13 and IL4, particularly in a house dust mite immunization model. Human IL13 expression was transgene copy number-dependent, suggesting BAC5 includes the human Th2 locus control region. Notably, DNA methylation patterns at multiple DNase I hypersensitive sites in the Th2 locus of human CD4 T cells were highly comparable if not identical in transgenic CD4 T cells of equivalent differentiation stages. Our results support the notion that in homologous tissues, genetic sequence is largely responsible for directing transcriptional programs and chromatin modifications even in a heterologous nuclear environment. Moreover, our findings suggest BAC5 transgenic mice are a powerful tool to study human Th2 cytokine gene regulation and Th2-dependent events in vivo.