Activation of RegIIIbeta/gamma and interferon gamma expression in the intestinal tract of SCID mice: an innate response to bacterial colonisation of the gut.

BACKGROUND AND AIMS: The mechanisms by which commensal bacteria provoke intestinal inflammation in animal models of inflammatory bowel disease (IBD) remain incompletely defined, leading to increasing interest in the innate immune response of the colonic mucosa to bacterial colonisation. METHODS: Using gene expression profiling of colonic RNA from C.B17.SCID germ free mice and those colonised with altered Schaedler's flora, we investigated the innate immune response to bacterial colonisation in vivo. The two most consistently induced gene groups were RegIIIbeta and gamma as well as interferon gamma (IFN-gamma) response genes. RESULTS: Using quantitative reverse transcription-polymerase chain reaction, we showed that RegIIIbeta, RegIIIgamma, and IFN-gamma were constitutively expressed in the colon of conventionally housed SCID mice compared with either germ free SCID or conventionally housed BALB/c mice. Induction of these genes was reproduced by chronic monoassociation of germ free SCID mice with either of two separate gut commensal bacterial species-segmented filamentous bacteria and Schaedler's Escherichia coli. The cellular source for IFN-gamma on monoassociation of SCID mice with Schaedler's E coli was localised to a subset of intraepithelial natural killer (IENK) cells that express asialo-GM1. In vivo IFN-gamma immunoneutralisation studies failed to demonstrate any alteration in RegIIIbeta or gamma expression. CONCLUSIONS: Thus bacterial colonisation of the colon independently activates two distinct innate immune cell types at the mucosal interface with the colonic lumen, intestinal epithelial cells, and IENK cells, a response that may be regulated by the adaptive immune system. These innate immune responses may play a role in the pathogenesis of colitis in SCID adoptive transfer models in mice and possibly in patients with IBD.

Colonic epithelial cell mediated suppression of CD4 T cell activation.

BACKGROUND AND AIMS: As the first point of contact with enteric antigens, intestinal epithelial cells (IEC) may be key in regulating mucosal immune responses. We determined therefore if murine colonic epithelial cells (CEC) have tolerogenic or activating effects on CD4 T cells. METHODS: Using a novel CEC, macrophages, and CD4 T cell coculture system, mitogen and antigen specific responses of naïve and antigen primed CD4 T cells were assessed. RESULTS: Although a proportion of CEC express the costimulatory molecules B7.1, B7.2, CD40, and CD54, they were unable to promote mitogen or antigen driven activation of CD4 T cells, even in the presence of exogenous costimulatory signals. CD4 T cells cocultured with CEC were CD25lo and CD45RBlo and remained in the G1 phase of the cell cycle. CEC were also able to prevent CD4 T cell activation by professional antigen presenting cells. CEC mediated suppression of T cell activation was cell contact dependent and transforming growth factor beta independent. CONCLUSIONS: These observations suggest that CEC contribute to the maintenance of T cell tolerance in the gut by preventing inappropriate activation of CD4 T cells.

Generation of human gammadelta T-cell repertoires.

The nature of how the human gammadelta T-cell repertoire is generated during normal development is poorly understood. Unlike TCR -alphabeta+ cells that are almost exclusively dependent upon the thymus for their development and maturation, gammadelta T cells can be generated in extrathymic sites. The focus of this article is to understand how the human gammadelta T-cell repertoire is generated during normal human development before and after birth. The expressed repertoire is a reflection of many mechanisms operating at both the DNA and protein levels, and we describe the features of the observed repertoires in various tissues in fetal and postnatal development and in the adult, and the potential mechanisms that account for them. Identifying the site(s) of origin and understanding how the various subsets of gammadelta T cells are generated is important for understanding their function. In addition, understanding how the gammadelta T-cell repertoire is modulated during life by infection, inflammation, and cancer should also bring us closer to understanding its function.

Mechanisms of immune cell-mediated tissue injury in inflammatory bowel disease (Review).

This review discusses the mechanisms and pathways of immune cell-mediated intestinal inflammation and tissue injury in inflammatory bowel disease (IBD). Our lack of understanding of how the mucosal immune system normally functions to maintain the balance between tolerance and immunity to innumerable dietary and bacterial constituents of the gut is perhaps the biggest obstacle to understanding the cause(s) of IBD, and to developing more effective treatments for these debilitating disorders. Evidence that abnormalities or disruptions in the interaction of immune cells and gut bacteria can trigger or contribute to changes in the composition, regulation and activity of the mucosal immune system that result in inflammatory immune responses and tissue injury are discussed. Based upon these studies, we propose a model to explain how a breakdown in regulation and failure to resolve immune responses in the gut mucosa results in persistent activation of T lymphocytes and other immune cells and the uncontrolled production of soluble inflammatory mediators that directly or indirectly produce the pathophysiological changes and tissue injury characteristic of IBD.

The generation of human gammadelta T cell repertoires during fetal development.

The nature of how human gammadelta T cells are normally generated is not clear. We have used an RT-PCR assay and DNA sequencing to identify and compare delta-encoded TCRs (TCRDs) that are generated de novo in the fetal gut, liver, and thymus and to determine when, where, and how the TCRD repertoire is established during normal embryonic development. Rearranged TCRDV genes are first expressed outside of the thymus in the liver and primitive gut between 6 and 9 wk gestation. Although DV1Rs and/or DV2Rs predominated, differences in the pattern of TCRDV gene rearrangement and transcription in each tissue during ontogeny were identified. Specific, DV2-encoded TCRs are highly conserved throughout ontogeny in the tissues from the same and between genetically distinct donors. Although the thymic and intestinal gammadelta T cell repertoires partially overlap early in development, they diverge and become nonoverlapping during the second trimester, and the generation of the intestinal gammadelta T cell repertoire is characterized by differences in the processing of DV1Rs and DV2Rs. Whereas the structural diversity of DV1Rs progressively increases during gut development up to birth, DV2Rs have limited structural diversity throughout ontogeny. Together, our findings provide evidence for the ability of different fetal tissues to support the development of gammadelta T cells.

Increased expression of tissue cytokines in graft-versus-host disease after small bowel transplantation in the rat.

BACKGROUND: Graft-versus-host disease (GVHD) occurs in the recipient after small bowel transplantation (SBT). Proinflammatory cytokines, such as tumor necrosis factor-alpha (TNF-alpha), interferon-gamma (IFN-gamma), and interleukin 6 (IL-6), may be important mediators of GVHD. Increased expression of these cytokines might precede the clinical manifestations of GVHD induced by SBT. METHODS: Heterotopic SBT was performed using Lewis donors into Lewis x Brown Norway F1 (LBN-F1) recipients. The isograft control was performed from LBN-F1 into LBN-F1. Animals were killed on the 5th and 11th postoperative day (POD). mRNA was isolated from recipient native small bowel, colon, spleen, liver, and mesenteric lymph nodes and from nonsurgical controls as baseline. Semiquantitative reverse transcriptase polymerase chain reaction was performed to amplify mRNA transcripts for TNF-alpha, IFN-gamma, and IL-6 using alpha32P-dATP incorporation. Clinical signs, histologic assessment, and cytokine expression were correlated. RESULTS: On POD 5, there were neither clinical signs nor histologic features of GVHD, but mRNA expression of TNF-alpha and IL-6 in small bowel, IL-6 in spleen, and IFN-gamma in mesenteric lymph nodes were significantly increased in allograft animals when compared with normal and isograft tissues. On POD 11, both the clinical signs and histologic features of GVHD were seen, and TNF-alpha and IL-6 in native small bowel, TNF-alpha in colon, IFN-gamma in spleen, and IL-6 in mesenteric lymph nodes were significantly increased in allograft animals when compared with that in normal and isograft tissues. CONCLUSIONS: In conclusion, TNF-alpha, IFN-gamma, and IL-6 expression precede clinical onset and histologic evidence of GVHD in specific tissues. Therefore, increased expression of these cytokines is correlated with the development of GVHD in this model of SBT.

Changes in human mucosal gamma delta T cell repertoire and function associated with the disease process in inflammatory bowel disease.

BACKGROUND: Although gamma delta T cells are a major component of the human intestinal mucosa, it is not clear what role they play in mucosal immunity or if they are involved in the disease process of inflammatory bowel disease (IBD). MATERIALS AND METHODS: Flow cytometry and reverse transcriptase-polymerase chain reaction (RT-PCR) assays were used to identify quantitative and qualitative changes in the repertoire of gamma delta T cells present in surgical and/or biopsy samples or normal and inflamed colon from individual patients with ulcerative colitis (UC) or Crohn's disease (CD). Cytokine production and the ability to adhere to and interact with colonic fibroblasts were used to compare the functional properties of gamma delta T cells isolated from the normal and diseased colonic mucosa. RESULTS: Increased numbers of gamma delta T cells localized in areas of inflammation and tissue injury were found in the majority of patients, irrespective of the type of IBD present. This expansion was attributable to an increase in V delta 1+ cells expressing a V delta 1-(D delta 3)-J delta 1-encoded T cell receptor and was seen in patients with severe disease as well as those with newly diagnosed or less severe forms of IBD. Among T cells present in the inflamed mucosa of patients with CD, gamma delta T cells, particularly V delta 1+ cells, were a major source of the proinflammatory cytokine interferon-gamma and could interact with colonic fibroblasts. CONCLUSIONS: Our results demonstrate that the chronic inflammatory immune response characteristic of IBD is associated with distinct changes in the number, distribution, composition, and function of mucosal gamma delta T cells. Through the production of cytokines and physical interaction with other cells, gamma delta T cells can perform an immunoregulatory function and contribute to the pathophysiology of IBDs.

Extrathymic origin of human gamma delta T cells during fetal development.

We have identified the first TCRs to be generated in vivo during normal human fetal development. Before thymic formation, the liver is a site of generation for a subset of V gamma 9/V delta 2+ gamma delta T cells. Analysis of the expression of the male-specific gene, SRY, by V gamma 9/V delta 2+ gamma delta T cells isolated from the fetal liver of male donors has shown that these cells are generated de novo in the liver. Examination of TCR-V gamma and -V delta gene expression demonstrated that although multiple receptor rearrangements could be detected, V gamma 9-JP- and V delta 2-D delta 3-J delta 1/3-encoded receptors were preferentially expressed in each of five individual liver samples. Structural analysis of these receptor chains and those expressed by a panel of V gamma 9/V delta 2+ fetal T cell clones showed that the V gamma 9-JP receptors were invariant or canonical and that the delta-chains contained non-germ line-encoded structural motifs. gamma delta T cells expressing these structurally limited receptor chains were shown to be functional and capable of responding to mycobacterial Ags. Together with the observation that V gamma 9/V delta 2+ cells represented the majority of T cells present in the fetal liver between 7 and 11 wk of development, our findings demonstrate that this subset of gamma delta T cells is a major, and presumably important, component of the human fetal immune system.

Regulated expression and structure of T cell receptor gamma/delta transcripts in human thymic ontogeny.

Gamma delta (gamma delta) T cells have been found in all vertebrates examined, yet their function in vivo remains unknown. Because gamma delta T cell receptors are related to immunoglobulin, and because they are encoded by rearranging, multi-gene families, the receptors are thought to be antigen recognition molecules. However, a capacity to recognize naturally diverse antigens has not yet been shown. In this work, the expression and structure of human gamma delta transcripts have been examined in the fetal and early post-natal thymus. The data indicate that many gamma and delta genes are rearranged and expressed throughout ontogeny, but that as ontogeny proceeds, quite dramatic changes occur in the patterns of gene expression and rearrangement. In particular, receptors encoded by early to mid-gestation fetal thymic transcripts would be of quite restricted diversity. Only later in ontogeny can receptors of substantial diversity be generated. These properties are very similar to the patterns of gamma delta gene activation in the mouse, and they serve to reiterate similarities both in gene rearrangement and in gamma delta across vertebrate species.

Pancreatic pseudotumor in pancreas divisum: CT characteristics.

We report a case in which a focally spared area of pancreatic tissue in a gland otherwise replaced by fat created a "pseudomass" mimicking neoplasm on sonography and CT. The "pseudomass" appearance was related to the anomalous ductal anatomy in pancreas divisum. The spared area of pancreas creating a "pseudomass" was drained by the dorsal duct and the remainder of the pancreas that had undergone relative fatty replacement was drained by the ventral duct.

Pancreas divisum: thin-section CT.

Twelve patients with known pancreas divisum underwent thin-section computed tomography (CT) to determine the capability of CT to depict this pancreatic anomaly. Focal pancreatic enlargement was present in five patients. Two distinct pancreatic moieties separated by a fat cleft were noted in three patients; a fourth patient had focal atrophy in the distribution of the dorsal pancreas. The two pancreatic moieties were identified at the same craniocaudal level in all four of these patients. The dorsal duct was depicted in all 12 patients, while the short ventral duct was seen in only five of the 12 patients. Failure of the ventral and dorsal pancreatic ducts to fuse was identified in all five patients in whom both ducts were seen. CT may not enable specific diagnosis of pancreas divisum in the majority of patients. If, however, distinct pancreatic moieties or unfused ductal systems are evident, the diagnosis may be confidently suggested.

The identification of ulcerative plaque with high resolution duplex carotid scanning.

A retrospective study evaluated 50 patients who had pathologically proven intraplaque hemorrhage. The patients were pathologically divided into two groups by the presence or absence of intimal ulcerations. These two groups were then sonographically compared with regard to surface characteristics of the plaque, plaque size, size of the sonolucent area within the plaque, and location of the sonolucent area relative to the intimal surface. No defined sonographic characteristics could be used to separate these two groups of patients with heterogeneous plaques into those who had or did not have ulcerations. Most importantly, merely sonographically evaluating the surface of the plaque to determine if it was smooth or irregular could not be used as a successful means to identify which patients were at risk for ulceration.

Ultrasonic characteristics of ileal tuberculosis.

Knowledge of the "pseudokidney sign" has proven beneficial in order to identify bowel lesions during ultrasound examinations. Numerous causes of the "pseudokidney sign" have been reported. Until now, however, there have been no published reports describing its association with tuberculosis. A description is given of a case of ileal tuberculosis identified by ultrasound, together with an explanation of its cause.

Quantitative variation in la antigen expression plays a central role in immune regulation.

The analysis of la antigen function has focused primarily on allelic variants of Ia molecules. In this review Charles Janeway and his colleagues discuss evidence that quantitative rather than qualitative variation in Ia antigen expression had a major role in immunoregulation and immunologically mediated disease.

Passive remote smoke plume opacity sensing: a technique.

A new passive technique for the remote measurement of the visual opacity of plumes emerging from smokestacks is presented. It is based on the detection of the attenuation of the polarized component of Rayleigh-scattered background skylight as it traverses a smoke plume. A two-color difference measurement of the polarization of skylight through the plume is compared with a similar measurement of the unattenuated skylight adjacent to the plume. This method is independent of the intrinsic brightness of the plume resulting from the scattering of sunlight and cancels white-light polarization effects of plume-scattered radiation. A prototype instrument incorporating this method has been successfully field tested on an EPA smoke school generator and a power plant stack plume.