Stephen J. Simpson

Severe colitis in mice with aberrant thymic selection

Tg epsilon 26 mice display an arrest very early in T cell development that has a profound effect on the architecture of thymic stromal cells. We have recently demonstrated that transplantation of wild-type bone marrow cells restores the thymic microenvironment of fetal but not adult Tg epsilon 26 mice. Here, we report that T cell-reconstituted adult Tg epsilon 26 mice develop a spontaneous wasting syndrome characterized by extensive inflammation of the colon, resembling human ulcerative colitis. Colitis in these animals was marked by substantial infiltration of the colon by activated thymus-derived CD4+ T cells. Importantly, bone marrow-transplanted Tg epsilon 26 mice previously engrafted with a fetal Tg epsilon 26 thymus did not develop colitis. These results suggest that T cells selected in an aberrant thymic microenvironment contain a population of cells able to induce severe colitis that can be prevented by T cells that have undergone normal thymic development.

Both the lymphotoxin and tumor necrosis factor pathways are involved in experimental murine models of colitis.

BACKGROUND & AIMS Membrane lymphotoxin (LT) alpha/beta, a member of the tumor necrosis factor (TNF) family of immune regulatory molecules, is involved both in the development of secondary lymphoid tissues and the maintenance of organized lymphoid tissues in the adult. Defects observed in the mucosal immune system in animals with a genetically disrupted LTalpha/beta pathway coupled with the expression of LTalpha/beta in activated T cells motivated an examination of the importance of this pathway in experimental colitis. METHODS Soluble LTbeta receptor (LTbetaR) immunoglobulin fusion protein was used to inhibit the LTalpha/beta/light axis in two independent rodent models of colitis: CD45RBhi CD4(+)-reconstituted SCID mice and bone marrow-transplanted tg26 mice (BM --> tg26). RESULTS Treatment with LTbetaR immunoglobulin attenuated the development of both the clinical and histological manifestations of the disease in these two murine models of colitis. Given the success of TNF inhibitors in the treatment of human Crohns disease, the effects of LTbetaR immunoglobulin have been compared with antibody to TNF in the BM --> tg26 model, and both treatments were equally efficacious. CONCLUSIONS The LT pathway plays a role in the development of colitis as important as that of the TNF system and, therefore, represents a potential novel intervention point for the treatment of inflammatory bowel disease.

Development and function of T lymphocytes and natural killer cells after bone marrow transplantation of severely immunodeficient mice

Summary: Bone marrow (BM) transplantation experiments were performed in a strain of CD3E‐transgenii: mice, termed tge26, which are completely deficient in T‐cell and natural killer (NK) cell development. We found that an interaction of stromal cells and prothymocytes is required for the induction of a cortical thymic microenvironment. This induction takes place in a time window from fetal development to early neonates. Although the thymic environment is not required for NK‐cell development, we found that aberrantly educated αβ or γδ T lymphocytes can influence NK‐cell ontogeny. Surprisingly, BM transplantation of tge26 fetuses and neonates results in normal T‐cell development, but very low levels of NK cells. The poor NK‐cell reconstitution in fetal and neonatal stages could be explained by an inefficient migration of hematopoietic progenitor ceils to the BM. By contrast, migration of the progenitor cells to the thymus was efficient to initiate T‐cell development, BM transplantation of adult tgE26 mice resulted in abnormal T‐cell development which, in turn, caused an inflammatory bowel disease (IBD) in the recipient mice. Studies in these BM chimeras have revealed that both αβ and γδ T cells can be pathogenic and, further, that Th 1‐like cytokines produced by these cells are causal factors in the pathogenesis of IBD.

Development of colonic adenocarcinomas in a mouse model of ulcerative colitis

Summary: Mice deficient in both interleukin‐2 and &bgr;2‐microglobulin expression (&bgr;2mnull × IL‐2null mice) develop an inflammatory disease of the colon resembling ulcerative colitis. To examine long‐term complications of disease in these mice, a group of 34 &bgr;2mnull × IL‐2null mice was monitored for 6‐12 months. Development of clinical disease was assessed by wasting, general appearance, and diarrhea. Further analysis included histologic examination of the distal colon for colitis, staining of CD4+ T cells for surface activation markers, and cytoplasmic staining of CD4+ T cells for IFN‐&ggr; and TNF‐&agr;. These older &bgr;2mnull × IL‐2null mice had activated CD4+ T cells as assessed by surface markers on flow cytometry. Cytoplasmic staining revealed IFN‐&ggr; production, but not TNF‐&agr; production by CD4+ T cells. The majority of these older &bgr;2mnull × IL‐2null mice continued to have colitis on histology. However, they lived much longer and had less wasting in comparison to IL‐2null mice. At necropsy, 11 (32%) of 34 of the &bgr;2mnull × IL‐2null mice had tumors in the proximal half of the colon. Histologic examination confirmed these tumors to be adenocarcinomas. These mice may be useful as a model for studying carcinogenesis in chronic colitis.

Consequences of Fas-Ligand and Perforin Expression by Colon T Cells in a Mouse Model of Inflammatory Bowel Disease

BACKGROUND & AIMS We describe a type of colitis that develops after transplantation of nonallogeneic wt bone marrow cells into T cell- and natural killer cell-deficient Tg26 mice (BM-->Tg26). In these animals, severe wasting and inflammation of the colon correlates with the expansion of mucosal T lymphocytes that displays cytotoxic activity. The aims of this study were to determine the relative contribution of perforin and Fas ligand (Fas-L) expression to the cytotoxic action of these T cells and to examine the influence of each pathway in this model of colitis. METHODS Colonic T cells were tested for their ability to mediate Fas- and perforin-dependent killing in redirected cytotoxicity assays. Bone marrow cells from donor mice lacking either Fas-L (gld mice) or perforin (PFPnull mice) or both molecules were used to reconstitute Tg26 mice. RESULTS Colon cytotoxic T lymphocyte displayed both Fas- and perforin-dependent killing. Deficiency in perforin, but not Fas-L, resulted in reduced incidence of wasting and, to a lesser extent, severe colitis in BM-->Tg26 animals. CONCLUSIONS Colon T cells from BM-->Tg26 mice express both perforin and Fas-L. Although neither pathway is critical in the development of colitis, perforin does have a measurable influence on disease in the BM-->Tg26 colitis model.

Pathways of T cell Pathology in Models of Chronic Intestinal Inflammation

The prominence of the immune system within the intestinal mucosa of the small and large bowel testifies to the importance of these organs as major sites of entry for pathogenic organisms. At the same time immune responses might equally be elicited to dietary antigens and commensal bacteria, yet it is only rarely that this appears to happen, demonstrating the tight regulation to which immune responses within the gastrointestinal (GI) tract are normally subject. Human inflammatory bowel diseases (IBD) arise from disturbances in immuno-regulation, appearing as seemingly spontaneous inflammation of the intestinal mucosa. Although some evidence exists for infectious etiology in IBD [I] evidence pointing towards a noninfectious component is plentiful, yet the initiating factors and the

Defects in T-Cell Regulation: Lessons for Inflammatory Bowel Disease

Publisher Summary The intestinal mucosa can pose a considerable risk if not kept under very tight control, as is clearly illustrated by the severe intestinal pathology that often accompanies human inflammatory bowel disease (IBD). IBD encompasses two related conditions, ulcerative colitis (UC) and Crohns disease (CD), that are thought to arise as immunopathological manifestations of a variety of initiating and predisposing factors. The recent emergence of a new generation of rodent IBD models born from refined and novel approaches to the manipulation of the immune system has generated new excitement in the field IBD research. Some of the first of the new spontaneous IBD models appeared as the unexpected consequence of targeted mutations of regulatory T-cell cytokine genes, including IL-2. The development of colitis in these animals was significant since it underscored the importance of cytokine-mediated regulation of pathogenic T cells. The studies of cytokine-deficient mice were complemented by others that demonstrated the importance of specific T-cell subsets in maintaining homeostasis within the mucosal lymphoid compartment.Publisher Summary The intestinal mucosa can pose a considerable risk if not kept under very tight control, as is clearly illustrated by the severe intestinal pathology that often accompanies human inflammatory bowel disease (IBD). IBD encompasses two related conditions, ulcerative colitis (UC) and Crohns disease (CD), that are thought to arise as immunopathological manifestations of a variety of initiating and predisposing factors. The recent emergence of a new generation of rodent IBD models born from refined and novel approaches to the manipulation of the immune system has generated new excitement in the field IBD research. Some of the first of the new spontaneous IBD models appeared as the unexpected consequence of targeted mutations of regulatory T-cell cytokine genes, including IL-2. The development of colitis in these animals was significant since it underscored the importance of cytokine-mediated regulation of pathogenic T cells. The studies of cytokine-deficient mice were complemented by others that demonstrated the importance of specific T-cell subsets in maintaining homeostasis within the mucosal lymphoid compartment.

Defects in T-Cell Regulation

Publisher Summary The intestinal mucosa can pose a considerable risk if not kept under very tight control, as is clearly illustrated by the severe intestinal pathology that often accompanies human inflammatory bowel disease (IBD). IBD encompasses two related conditions, ulcerative colitis (UC) and Crohns disease (CD), that are thought to arise as immunopathological manifestations of a variety of initiating and predisposing factors. The recent emergence of a new generation of rodent IBD models born from refined and novel approaches to the manipulation of the immune system has generated new excitement in the field IBD research. Some of the first of the new spontaneous IBD models appeared as the unexpected consequence of targeted mutations of regulatory T-cell cytokine genes, including IL-2. The development of colitis in these animals was significant since it underscored the importance of cytokine-mediated regulation of pathogenic T cells. The studies of cytokine-deficient mice were complemented by others that demonstrated the importance of specific T-cell subsets in maintaining homeostasis within the mucosal lymphoid compartment.Publisher Summary The intestinal mucosa can pose a considerable risk if not kept under very tight control, as is clearly illustrated by the severe intestinal pathology that often accompanies human inflammatory bowel disease (IBD). IBD encompasses two related conditions, ulcerative colitis (UC) and Crohns disease (CD), that are thought to arise as immunopathological manifestations of a variety of initiating and predisposing factors. The recent emergence of a new generation of rodent IBD models born from refined and novel approaches to the manipulation of the immune system has generated new excitement in the field IBD research. Some of the first of the new spontaneous IBD models appeared as the unexpected consequence of targeted mutations of regulatory T-cell cytokine genes, including IL-2. The development of colitis in these animals was significant since it underscored the importance of cytokine-mediated regulation of pathogenic T cells. The studies of cytokine-deficient mice were complemented by others that demonstrated the importance of specific T-cell subsets in maintaining homeostasis within the mucosal lymphoid compartment.

Chapter 22 – Defects in T-Cell Regulation: Lessons for Inflammatory Bowel Disease

Publisher Summary The intestinal mucosa can pose a considerable risk if not kept under very tight control, as is clearly illustrated by the severe intestinal pathology that often accompanies human inflammatory bowel disease (IBD). IBD encompasses two related conditions, ulcerative colitis (UC) and Crohns disease (CD), that are thought to arise as immunopathological manifestations of a variety of initiating and predisposing factors. The recent emergence of a new generation of rodent IBD models born from refined and novel approaches to the manipulation of the immune system has generated new excitement in the field IBD research. Some of the first of the new spontaneous IBD models appeared as the unexpected consequence of targeted mutations of regulatory T-cell cytokine genes, including IL-2. The development of colitis in these animals was significant since it underscored the importance of cytokine-mediated regulation of pathogenic T cells. The studies of cytokine-deficient mice were complemented by others that demonstrated the importance of specific T-cell subsets in maintaining homeostasis within the mucosal lymphoid compartment.Publisher Summary The intestinal mucosa can pose a considerable risk if not kept under very tight control, as is clearly illustrated by the severe intestinal pathology that often accompanies human inflammatory bowel disease (IBD). IBD encompasses two related conditions, ulcerative colitis (UC) and Crohns disease (CD), that are thought to arise as immunopathological manifestations of a variety of initiating and predisposing factors. The recent emergence of a new generation of rodent IBD models born from refined and novel approaches to the manipulation of the immune system has generated new excitement in the field IBD research. Some of the first of the new spontaneous IBD models appeared as the unexpected consequence of targeted mutations of regulatory T-cell cytokine genes, including IL-2. The development of colitis in these animals was significant since it underscored the importance of cytokine-mediated regulation of pathogenic T cells. The studies of cytokine-deficient mice were complemented by others that demonstrated the importance of specific T-cell subsets in maintaining homeostasis within the mucosal lymphoid compartment.