We describe here the immunologic characterization of a new mouse strain, SAMP1/Yit, which spontaneously develops a chronic intestinal inflammation localized to the terminal ileum. The resulting ileitis bears a remarkable resemblance to human Crohn's disease. This strain of mice develops discontinuous, transmural inflammatory lesions in the terminal ileum with 100% penetrance by 30 weeks of age. The intestinal inflammation is characterized by massive infiltration of activated CD4+ and CD8alpha(+)TCRalphabeta(+) T cells into the lamina propria and is accompanied by a dramatic decrease in the intraepithelial lymphocyte CD8alpha(+)TCRgammadelta(+)/CD8alpha(+)TCRalphabeta(+) ratio. The results of adoptive transfer experiments strongly suggest that CD4+ T cells that produce a Th1-like profile of cytokines, e.g., IFN-gamma and TNF, mediate the intestinal inflammation found in SAMP1/Yit mice. In addition, pretreatment of adoptive transfer recipients with a neutralizing anti-TNF antibody prevents the development of intestinal inflammation, suggesting that TNF plays an important role in the pathogenesis of intestinal inflammation in this model. To our knowledge, these data provide the first direct evidence that Th1-producing T cells mediate intestinal inflammation in a spontaneous animal model of human Crohn's disease.

The CD4+ CD25+ regulatory T cells play a critical role in controlling autoimmunity, but little is known about their development and maintenance. In this study, we investigated whether CD4+ CD25− cells can convert to CD4+ CD25+ regulatory T cells in vivo under natural conditions. CD4+ CD25− cells from CD45.1+ mice were sorted and transferred into congenic CD45.2+ mice. Converted CD4+ CD25+ cells could be detected in lymphoid organs as early as 1 wk after transfer and by 6 wk after transfer, 5–12% of transferred CD4+ cells expressed CD25. Converted CD4+ CD25+ cells themselves failed to proliferate after stimulation, but could suppress proliferation of responder cells in vitro, and also expressed high levels of Foxp3 mRNA. In addition, CD4+ CD25− cells transferred into thymectomized congenic mice converted to CD4+ CD25+ cells that also suppressed responder cell proliferation in vitro, and expressed high levels of Foxp3 mRNA. Finally, CD4+ CD25− cells transferred into B7−/− mice failed to convert into CD4+ CD25+ cells that exhibit the regulatory phenotype. These data indicate that CD4+ CD25− cells convert into CD4+ CD25+ regulatory T cells spontaneously in vivo and suggest that this conversion process could contribute significantly to the maintenance of the peripheral CD4+ CD25+ regulatory T cell population.

A single intratumoral injection of IL-12 and GM-CSF-loaded slow-release microspheres induces T cell-dependent eradication of established primary and metastatic tumors in a murine lung tumor model. To determine how the delivery of cytokines directly to the microenvironment of a tumor nodule induces local and systemic antitumor T cell activity, we characterized therapy-induced phenotypic and functional changes in tumor-infiltrating T cell populations. Analysis of pretherapy tumors demonstrated that advanced primary tumors were infiltrated by CD4+ and CD8+ T cells with an effector/memory phenotype and CD4+CD25+Foxp3+ T suppressor cells. Tumor-associated effector memory CD8+ T cells displayed impaired cytotoxic function, whereas CD4+CD25+Foxp3+ cells effectively inhibited T cell proliferation demonstrating functional integrity. IL-12/GM-CSF treatment promoted a rapid up-regulation of CD43 and CD69 on CD8+ effector/memory T cells, augmented their ability to produce IFN-γ, and restored granzyme B expression. Importantly, treatment also induced a concomitant and progressive loss of T suppressors from the tumor. Further analysis established that activation of pre-existing effector memory T cells was short-lived and that both the effector/memory and the suppressor T cells became apoptotic within 4 days of treatment. Apoptotic death of pre-existing effector/memory and suppressor T cells was followed by infiltration of the tumor with activated, nonapoptotic CD8+ effector T lymphocytes on day 7 posttherapy. Both CD8+ T cell activation and T suppressor cell purge were mediated primarily by IL-12 and required IFN-γ. This study provides important insight into how local IL-12 therapy alters the immunosuppressive tumor milieu to one that is immunologically active, ultimately resulting in tumor regression.

Our immune system has evolved to recognize and eradicate pathogenic microbes. However, we have a symbiotic relationship with multiple species of bacteria that occupy the gut and comprise the natural commensal flora or microbiota. The microbiota is critically important for the breakdown of nutrients, and also assists in preventing colonization by potentially pathogenic bacteria. In addition, the gut commensal bacteria appear to be critical for the development of an optimally functioning immune system. Various studies have shown that individual species of the microbiota can induce very different types of immune cells (e.g., Th17 cells, Foxp3+ regulatory T cells) and responses, suggesting that the composition of the microbiota can have an important influence on the immune response. Although the microbiota resides in the gut, it appears to have a significant impact on the systemic immune response. Indeed, specific gut commensal bacteria have been shown to affect disease development in organs other than the gut, and depending on the species, have been found to have a wide range of effects on diseases from induction and exacerbation to inhibition and protection. In this review, we will focus on the role that the gut microbiota plays in the development and progression of inflammatory/autoimmune disease, and we will also touch upon its role in allergy and cancer.

a b s t r a c tThe interplay between the immune response and the gut microbiota is complex. Although it is well-established that the gut microbiota is essential for the proper development of the immune system, recent evidence indicates that the cells of the immune system also influence the composition of the gut microbiota. This interaction can have important consequences for the development of inflammatory diseases, including autoimmune diseases and allergy, and the specific mechanisms by which the gut commensals drive the development of different types of immune responses are beginning to be understood. Furthermore, sex hormones are now thought to play a novel role in this complex relationship, and collaborate with both the gut microbiota and immune system to influence the development of autoimmune disease. In this review, we will focus on recent studies that have transformed our understanding of the importance of the gut microbiota in inflammatory responses. Ó 2014 Federation of European Biochemical Societies. Published by Elsevier B.V. All rights reserved. Regulation of the immune response by the gut microbiotaThe commensal bacteria, or microbiota, colonizing the gut performs several functions: it plays a critical role in the breakdown of indigestible complex plant polysaccharides, synthesizes important nutrients such as vitamin K, and provides an important layer of defense against invasion by pathogenic microorganisms. Interestingly, the intestinal microbiota affects the immune and/or inflammatory status of the host by modulating intestinal barrier function and by influencing the development of the immune response. Several gut microbial structures that play an important role in barrier functions have been identified. The secreted protein, p40, from Lactobacilli LGG ameliorates cytokine-mediated apoptosis and disruption of the gut epithelial barrier [1], and flagellin from Escherichia coli Nissle is associated with induction of b-defensin 2 in epithelial cells [2]. Gut microbiota has been shown to direct maturation of the host immune system [3], to play a key role in the induction of immunoglobulin (Ig) A [4,5] and germinal centers [6], and to drive Th1, Th17, and regulatory T cell (Treg) development in the gut [7][8][9]. In most individuals, the commensal-mediated induction of these different components of the immune response is beneficial for host health. However, the composition of the gut microbiota can differentially influence various immune cell populations and adversely affect autoimmune/inflammatory disease-susceptible hosts, e.g., the presence of segmented filamentous bacteria (SFB) has been associated with a strong Th17 response and development of Th17-mediated diseases [10][11][12].Colonic commensal bacteria may ''educate'' both thymically and peripherally-derived regulatory T cells. One study using mice transgenic for T cells expressing a limited, but diverse [i.e., express identical T cell receptor (TCR) b], TCR repertoire showed that the TCR repertoire of colonic Tregs is unique (i.e., is not e...

Various defects in antigen-presenting cells (APCs) and T-cells, including regulatory cells, have been associat-

Transforming growth factor g (TGF g )-treated antigen-presenting cells (APC) pulsed with antigen induce tolerance in mice, i.e. inhibition of IFN-+ production and delayed type hypersensitivity response. Although evidence suggests that regulatory T cells are involved, their mechanism of action is currently unknown and is the subject of the present study. Both CD4 and CD8 splenic T cells from mice injected i.v. with adherent thioglycolate-elicited peritoneal exudate cells cultured with TGF g 2 and antigen (TGF g -treated APC) transferred tolerance to naive recipients. Interestingly, TGF g -treated APC from class II knockout mice were unable to induce tolerance in wild-type mice, whereas wild-type TGF g -treated APC could induce tolerance in CD8 knockout mice. TGF g was detected in cultures of lymphoid cells from mice injected with TGF g -treated APC, and treatment with anti-TGF g antibody in vivo impaired tolerance induction. TGF g appeared to be involved in both the development of CD4 regulatory T cells and the effector function of the CD4 regulatory T cells. In summary, the important findings in this study are that CD4, and not CD8, regulatory T cells are required for tolerance induced by TGF g -treated APC in naive mice, and tolerance appears to be mediated by a mechanism involving TGF g .

The CD4(+)CD25(+)Foxp3(+) cells are essential for regulation of the immune response, and the integrin, CD103 (α(E)β(7)), identifies a potent subset of these cells. Defects in CD4(+)CD25(+)Foxp3(+) cells are thought to contribute to susceptibility to autoimmune disease in predisposed individuals. Studies evaluating the quality and quantity of CD4(+)CD25(+)Foxp3(+) regulatory cell populations in the context of autoimmune disease susceptibility have been inconclusive, and few if any, have analyzed the CD103 subset. In this study, we analyzed regulatory T cells (Tregs) from different strains of mice with varying degrees of susceptibility to autoimmune disease. We found no differences in the ability of CD4(+)CD25(+) or the CD103(+) subset of Tregs from young female (NZB × NZW)F1 (BWF1), SJL, C57BL/6, or BALB/c mice to suppress CD4(+)CD25(- ) responders in vitro. Analysis of CD4(+)Foxp3(+) and CD4(+)CD25(+)CD103(+) cell frequencies in lymphoid organs revealed that BWF1 mice had dramatically lower percentages of both populations in the lymph node (LN) than the other strains, and lower percentages in the spleen in all but the C57BL/6 strain. We next determined whether these findings extended to another autoimmune-prone strain. Similar to BWF1 mice, percentages of CD4(+)Foxp3(+) and CD4(+)CD25(+)CD103(+) cells were significantly lower in predisease NOD mice. The low frequencies of CD4(+)Foxp3(+) and CD4(+)CD25(+)CD103(+) cells in BWF1 and NOD mice were not due to deficiencies in either thymic production or homeostatic proliferation. These data indicate that decreased percentages of CD4(+)Foxp3(+) cells and particularly, CD4(+)CD25(+)CD103(+) cells in LN correlate with the predisposition to spontaneous development of autoimmune disease.