Colitis-inducing potency of CD4+ T cells in immunodeficient, adoptive hosts depends on their state of activation, IL-12 responsiveness, and CD45RB surface phenotype

We studied the induction, severity and rate of progression of inflammatory bowel disease (IBD) induced in SCID mice by the adoptive transfer of low numbers of the following purified BALB/c CD4+ T cell subsets: 1) unfractionated, peripheral, small (resting), or large (activated) CD4+ T cells; 2) fractionated, peripheral, small, or large, CD45RBhigh or CD45RBlow CD4+ T cells; and 3) peripheral IL-12-unresponsive CD4+ T cells from STAT-4-deficient mice. The adoptive transfer into SCID host of comparable numbers of CD4+ T cells was used to assess the colitis-inducing potency of these subsets. Small CD45RBhigh CD4+ T lymphocytes and activated CD4+ T blasts induced early (6-12 wk posttransfer) and severe disease, while small resting and unfractionated CD4+ T cells or CD45RBlow T lymphocytes induced a late-onset disease 12-16 wk posttransfer. SCID mice transplanted with STAT-4-/- CD4+ T cells showed a late-onset IBD manifest > 20 wk posttransfer. In SCID mice with IBD transplanted with IL-12-responsive CD4+ T cells, the colonic lamina propria CD4+ T cells showed a mucosa-seeking memory/effector CD45RBlow Th1 phenotype abundantly producing IFN-gamma and TNF-alpha. In SCID mice transplanted with IL-12-unresponsive STAT-4-/- CD4+ T cells, the colonic lamina propria, mesenteric lymph node, and splenic CD4+ T cells produced very little IFN-gamma but abundant levels of TNF-alpha. The histopathologic appearance of colitis in all transplanted SCID mice was similar. These data indicate that CD45RBhigh and CD45RBlow, IL-12-responsive and IL-12-unresponsive CD4+ T lymphocytes and lymphoblasts have IBD-inducing potential though of varying potency.     

CD69 regulates type I IFN-induced tolerogenic signals to mucosal CD4 T cells that attenuate their colitogenic potential

CD69 is highly expressed by lymphocytes at mucosal surfaces. We aimed to investigate the role of CD69 in mucosal immune responses. The expression of CD69 by CD4 T cells isolated from the spleen, mesenteric lymph nodes, small intestinal lamina propria, and colonic lamina propria was determined in specific pathogen-free B6 and TCR transgenic animals, as well as in germ-free B6 mice. Transfer colitis was induced by transplanting RAG(-/-) mice with B6 or CD69(-/-)CD45RB(high) CD4 T cells. CD69 expression by CD4 T cells is induced by the intestinal microflora, oral delivery of specific Ag, and type I IFN (IFN-I) signals. CD4 T cells from CD69(-/-) animals produce higher amounts of the proinflammatory cytokines IFN-γ, TNF-α, and IL-21, whereas the production of TGF-β1 is decreased. CD69-deficient CD4 T cells showed reduced potential to differentiate into Foxp3(+) regulatory T cells in vivo and in vitro. The transfer of CD69(-/-)CD45RB(high) CD4 T cells into RAG(-/-) hosts induced an accelerated colitis. Oral tolerance was impaired in CD69(-/-) and IFN-I receptor 1-deficient mice when compared with B6 and OT-II × RAG(-/-) animals. Polyinosinic-polycytidylic acid treatment of RAG(-/-) mice transplanted with B6 but not CD69(-/-) or IFN-I receptor 1-deficient CD45RB(high) CD4 T cells attenuated transfer colitis. CD69 deficiency led to the increased production of proinflammatory cytokines, reduced Foxp3(+) regulatory T cell induction, impaired oral tolerance, and more severe colitis. Hence, the activation Ag CD69 plays an important role in regulating mucosal immune responses.     

Impact of CCR7 on the gastrointestinal field effect

Standardized intestinal manipulation (IM) leads to local bowel wall inflammation subsequently spreading over the entire gastrointestinal tract. Previously, we demonstrated that this so-called gastrointestinal field effect (FE) is immune mediated. This study aimed to investigate the role of CCR7 in IM-induced FE. Since CCR7 is expressed on activated dendritic cells and T cells and is well known to control their migration, we hypothesized that lack of CCR7 reduces or abolishes FE. Small bowel muscularis and colonic muscularis from CCR7(-/-) and wild-type (WT) mice were obtained after IM of the jejunum or sham operation. FE was analyzed by measuring gastrointestinal transit time of orally given fluorescent dextran (geometric center), colonic transit time, infiltration of MPO-positive cells, and circular smooth muscle contractility. Furthermore, mRNA levels of the inflammatory cytokine IL-6 were determined by RT-PCR. The number of dendritic cells and CD3+CD25+ T cells separately isolated from jejunum and colon was determined in mice after IM and sham operation. There was no significant difference in IL-6 mRNA upregulation in colonic muscularis between sham-operated WT and CCR7(-/-) mice after IM. Contractility of circular muscularis strips of the colon was significantly improved in CCR7(-/-) animals following IM and did not vary significantly from sham-operated animals. Additionally, inflammation of the colon determined by the number of MPO-positive cells and colonic transit time was significantly reduced in CCR7(-/-) mice. In contrast, jejunal contractility and jejunal inflammation of transgenic mice did not differ significantly from WT mice after IM. These data are supported by a significant increase of CD3+CD25+ T cells in the colonic muscularis of WT mice after IM, which could not be observed in CCR7(-/-) mice. These data demonstrate that CCR7 is required for FE and postoperative ileus. CCR7 indirectly affects FE by inhibiting migration of activated dendritic cells and of T cells from the jejunum to the colon. These findings support the critical role of the adaptive immune system in FE.     

The critical role of LIGHT in promoting intestinal inflammation and Crohn's disease

Crohn's disease (CD) is a type of inflammatory bowel disease associated with increased Th1 cytokines and unique pathological features. However, its pathogenesis has not been fully understood. Previous studies showed that homologous to lymphotoxin, exhibits inducible expression, competes with herpesvirus glycoprotein D for HVEM on T cells (LIGHT) transgenic (Tg) mice develop autoimmunity including intestinal inflammation with a variable time course. In this study, we establish an experimental model for CD by adoptive transfer of Tg mesenteric lymph node cells into RAG(-/-) mice. The recipients of Tg lymphocytes rapidly develop a disease strikingly similar to the key pathologic features and cytokine characterization observed in CD. We demonstrate that, as a costimulatory molecule, LIGHT preferentially drives Th1 responses. LIGHT-mediated intestinal disease is dependent on both of its identified signaling receptors, lymphotoxin beta receptor and herpes virus entry mediator, because LIGHT Tg mesenteric lymph node cells do not cause intestinal inflammation when transferred into the lymphotoxin beta receptor-deficient mice, and herpes virus entry mediator on donor T cells is required for the full development of disease. Furthermore, we demonstrated that up-regulation of LIGHT is associated with active CD. These data establish a new mouse model resembling CD and suggest that up-regulation of LIGHT may be an important mediator of CD pathogenesis.     

In vivo adjuvant-induced mobilization and maturation of gut dendritic cells after oral administration of cholera toxin

Although dendritic cells (DCs) regulate immune responses, they exhibit functional heterogeneity depending on their anatomical location. We examined the functional properties of intestinal DCs after oral administration of cholera toxin (CT), the most potent mucosal adjuvant. Two CD11c+ DC subsets were identified both in Peyer's patches and mesenteric lymph nodes (MLN) based on the expression of CD8alpha (CD8+ and CD8- DCs, respectively). A third subset of CD11c+CD8int was found exclusively in MLN. Feeding mice with CT induced a rapid and transient mobilization of a new CD11c+CD8- DC subset near the intestinal epithelium. This recruitment was associated with an increased production of the chemokine CCL20 in the small intestine and was followed by a massive accumulation of CD8int DCs in MLN. MLN DCs from CT-treated mice were more potent activators of naive T cells than DCs from control mice and induced a Th2 response. This increase in immunostimulating properties was accounted for by CD8int and CD8- DCs, whereas CD8+ DCs remained insensitive to CT treatment. Consistently, the CD8int and CD8- subsets expressed higher levels of costimulatory molecules than CD8+ and corresponding control DCs. Adoptive transfer experiments showed that these two DC subsets, unlike CD8+ DCs, were able to present Ags orally coadministered with CT in an immunostimulating manner. The ability of CT to mobilize immature DCs in the intestinal epithelium and to promote their emigration and differentiation in draining lymph nodes may explain the exceptional adjuvant properties of this toxin on mucosal immune responses.     

Mice with a selective deletion of the CC chemokine receptors 5 or 2 are protected from dextran sodium sulfate-mediated colitis: lack of CC chemokine receptor 5 expression results in a NK1.1+ lymphocyte-associated Th2-type immune response in the intestine

The chemokine receptors CCR2 and CCR5 and their respective ligands regulate leukocyte chemotaxis and activation. To determine the role of these chemokine receptors in the regulation of the intestinal immune response, we induced colitis in CCR2- and CCR5-deficient mice by continuous oral administration of dextran sodium sulfate (DSS). Both CCR2- and CCR5-deficient mice were susceptible to DSS-induced intestinal inflammation. The lack of CCR2 or CCR5 did not reduce the DSS-induced migration of macrophages into the colonic lamina propria. However, both CCR5-deficient mice and, to a lesser degree, CCR2-deficient mice were protected from DSS-induced intestinal adhesions and mucosal ulcerations. CCR5-deficient mice were characterized by a greater relative infiltration of CD4+ and NK1.1+ lymphocyte in the colonic lamina propria when compared to wild-type and CCR2-deficient mice. In CCR5-deficient mice, mucosal mRNA expression of IL-4, IL-5, and IL-10 was increased, whereas that of IFN-gamma was decreased, corresponding to a Th2 pattern of T cell activation. In CCR2-deficient mice, the infiltration of Th2-type T cells in the lamina propria was absent, but increased levels of IL-10 and decreased levels of IFN-gamma may have down regulated mucosal inflammation. Our data indicate that CCR5 may be critical for the promotion of intestinal Th1-type immune responses in mice.     

CD4+CD25+ regulatory cells contribute to the regulation of colonic Th2 granulomatous pathology caused by schistosome infection

Eggs of the helminth Schistosoma mansoni accumulate in the colon following infection and generate Th2-biassed inflammatory granulomas which become down- modulated in size as the infection proceeds to chronicity. However, although CD4+CD25+FoxP3+ regulatory T cells (T(regs)) are known to suppress Th1-mediated colitis, it is not clear whether they control Th2-associated pathologies of the large intestine which characterise several helminth infections. Here we used a novel 3D-multiphoton confocal microscopy approach to visualise and quantify changes in the size and composition of colonic granulomas at the acute and chronic phases of S. mansoni infection. We observed decreased granuloma size, as well as reductions in the abundance of DsRed+ T cells and collagen deposition at 14 weeks (chronic) compared to 8 weeks (acute) post-infection. Th2 cytokine production (i.e. IL-4, IL-5) in the colonic tissue and draining mesenteric lymph node (mLN) decreased during the chronic phase of infection, whilst levels of TGF-β1 increased, co-incident with reduced mLN proliferative responses, granuloma size and fibrosis. The proportion of CD4+CD25+FoxP3+T(regs): CD4+ cells in the mLN increased during chronic disease, while within colonic granulomas there was an approximate 4-fold increase. The proportion of CD4+CD25+FoxP3+T(regs) in the mLN that were CD103+ and CCR5+ also increased indicating an enhanced potential to home to intestinal sites. CD4+CD25+ cells suppressed antigen-specific Th2 mLN cell proliferation in vitro, while their removal during chronic disease resulted in significantly larger granulomas, partial reversal of Th2 hypo-responsiveness and an increase in the number of eosinophils in colonic granulomas. Finally, transfer of schistosome infection-expanded CD4+CD25+T(regs) down-modulated the development of colonic granulomas, including collagen deposition. Therefore, CD4+CD25+FoxP3+T(regs) appear to control Th2 colonic granulomas during chronic infection, and are likely to play a role in containing pathology during intestinal schistosomiasis.     

Administration of mAb against alpha E beta 7 prevents and ameliorates immunization-induced colitis in IL-2-/- mice

We previously demonstrated that 2,4,6-trinitrophenol (TNP)-OVA immunization leads to a transmural colitis in the IL-2-/- mouse that is caused by IL-12-driven CD4+ Th1 T cells and resembles human Crohn's disease. The integrin alpha E beta 7 is highly expressed on colonic intraepithelial lymphocytes and has been suggested to function as a homing or retention molecule for intraepithelial lymphocytes. To evaluate the role of alpha E beta 7 in colitis, we administered a mAb against alpha E beta 7 to IL-2-/- mice that were immunized at the same time with TNP-OVA in CFA. To our surprise, this treatment resulted in a significantly reduced colitis severity score, 0-2 vs 3-4, that was associated with a significant reduction in CD4+ lamina propria lymphocyte subpopulation (p < 0.01). In contrast, the total number of splenic CD4+ T cells of treated animals was significantly elevated compared with that of untreated animals (3.2 +/- 0.6 x 107 vs 1.2 +/- 0.2 x 107; p < 0.05). Similarly, functional studies revealed that IFN-gamma production by lamina propria lymphocytes isolated from IL-2-/- TNP-OVA-immunized mice treated with anti-alpha E beta 7 was significantly lower than in untreated IL-2-/- TNP-OVA-immunized mice. In contrast, IFN-gamma production by splenic cells isolated from treated IL-2-/- TNP-OVA-immunized mice was significantly higher than in untreated mice. Finally, TNP-OVA-immunized IL-2-/- mice that were treated after the colitis had been established also showed a significant decrease in mucosal inflammation after alpha E beta 7 mAb administration. Thus, the above findings demonstrate that the onset and maintenance of inflammatory bowel disease depends on the colonic localization of lamina propria CD4+ lymphocytes expressing alpha E beta 7.     

CD8+ alpha/beta or gamma/delta T cell receptor-bearing T cells from athymic nude mice are cytolytically active in vivo.

Phenotypic analysis of lymphocytes that mature extrathymically in congenitally athymic nude mice has revealed a large population of CD3+ CD8+ T cells that express gamma/delta-TCR. In euthymic mice, significant numbers of cells with this phenotype are found only in the intestinal epithelium. Intestinal intraepithelial lymphocytes have been shown to be cytolytically active in vivo, as measured by the redirected lysis assay. In this communication, freshly harvested T cell subsets obtained from pooled nude mouse spleen and lymph nodes and separated by flow cytometric cell sorting were assayed for their ability to lyse FcR+ P815 targets in the presence of mAb to the epsilon-chain of the CD3 complex. CD8+, but not CD4+ or CD4- CD8-, T cells in nude mice were cytolytically active. CD8+ alpha/beta- and gamma/delta-TCR-bearing T cells from the spleen and lymph nodes of nude mice demonstrated similar cytolytic activity. No cytolytic activity of purified cell subsets was apparent in the absence of anti-CD3 mAb, even when NK-susceptible target cells were used. These data indicate that, in contrast to euthymic mice, a large proportion of CD8+ cells from the spleen and lymph nodes of nude mice are cytolytically active in vivo. In addition, these results suggest that the intestinal epithelium is not the only anatomical location where constitutively cytolytic CD8+ alpha/beta- or gamma/delta TCR-bearing T cells may be found.     

Intestinal epithelial antigen induces mucosal CD8 T cell tolerance, activation, and inflammatory response

Intestinal autoimmune diseases are thought to be associated with a breakdown in tolerance, leading to mucosal lymphocyte activation perhaps as a result of encounter with bacterium-derived Ag. To study mucosal CD8(+) T cell activation, tolerance, and polarization of autoimmune reactivity to self-Ag, we developed a novel (Fabpl(4x at -132)-OVA) transgenic mouse model expressing a truncated form of OVA in intestinal epithelia of the terminal ileum and colon. We found that OVA-specific CD8(+) T cells were partially tolerant to intestinal epithelium-derived OVA, because oral infection with Listeria monocytogenes-encoding OVA did not elicit an endogenous OVA-specific MHC class I tetramer(+)CD8(+) T cell response and IFN-gamma-, IL-4-, and IL-5-secreting T cells were decreased in the Peyer's patches, mesenteric lymph nodes, and intestinal mucosa of transgenic mice. Adoptive transfer of OVA-specific CD8(+) (OT-I) T cells resulted in their preferential expansion in the Peyer's patches and mesenteric lymph nodes and subsequently in the epithelia and lamina propria but failed to cause mucosal inflammation. Thus, CFSE-labeled OT-I cells greatly proliferated in these tissues by 5 days posttransfer. Strikingly, OT-I cell-transferred Fabpl(4x at -132)-OVA transgenic mice underwent a transient weight loss and developed a CD8(+) T cell-mediated acute enterocolitis 5 days after oral L. monocytogenes-encoding OVA infection. These findings indicate that intestinal epithelium-derived "self-Ag" gains access to the mucosal immune system, leading to Ag-specific T cell activation and clonal deletion. However, when Ag is presented in the context of bacterial infection, the associated inflammatory signals drive Ag-specific CD8(+) T cells to mediate intestinal immunopathology.     

CD1-restricted recognition of exogenous and self-lipid antigens by duodenal gammadelta+ T lymphocytes

Gammadelta T cells are present in the mucosal intestinal epithelia and secrete factors necessary to maintain tissue integrity. Ags recognized by these cells are poorly defined, although in mice non-classical MHC class I molecules have been implicated. Since MHC class I-like CD1 receptors are widely expressed at the surface of epithelial and dendritic intestinal cells and have the capacity to present lipid Ags to T cells, we hypothesized that these molecules might present autologous and/or exogenous phospholipids to intestinal gammadelta T lymphocytes. Intraepithelial T lymphocytes from normal human duodenal mucosal biopsies were cloned and exposed to natural and synthetic phospholipids using CD1a-, CD1b-, CD1c- or CD1d-transfected C1R lymphoblastoid or HeLa cell lines as APCs. Their cytolytic properties and regulatory cytokine secretion were also examined. Most clones obtained from duodenal mucosa (up to 70%) were TCRalphabeta+, and either CD4+ or CD8+, whereas 20% were CD4-CD8- (6 clones) or TCRgammadelta+ (12 clones). A relevant percentage (up to 66%) of TCRgammadelta+ but few (<5%) TCRalphabeta+ T cell clones responded to synthetic and/or natural phospholipids presented by CD1 molecules, as measured by both [(3)H]thymidine incorporation and IL-4 release assays. A Th1-like cytolytic and functional activity along with the ability to secrete regulatory cytokines was observed in most phospholipid-specific gammadelta T cell clones. Thus, a substantial percentage of TCRgammadelta+ but few TCRalphabeta+ from human duodenal mucosa recognize exogenous phospholipids in a CD1-restricted fashion. This adaptive response could contribute to mucosal homeostasis, but could also favor the emergence of inflammatory or allergic intestinal diseases.     

Alteration of V beta usage and cytokine production of CD4+ TCR beta beta homodimer T cells by elimination of Bacteroides vulgatus prevents colitis in TCR alpha-chain-deficient mice

A major pathogenic factor for the development of inflammatory bowel disease (IBD) is the breakdown of the intestinal homeostasis between the host immune system and the luminal microenvironment. To assess the potential influence of luminal Ags on the development of IBD, we fed TCR alpha(-/-) mice an elemental diet (ED). ED-fed TCR alpha(-/-) mice showed no pathologic features of IBD, and their aberrant mucosal B cell responses were suppressed. Similar numbers of CD4(+), TCR betabeta homodimer T cells (betabeta T cells) were developed in the colonic mucosa of ED-fed mice; however, Th2-type cytokine productions were lower than those seen in diseased regular diet (RD)-fed mice. The higher cytokine production in diseased RD-fed mice could be attributed to the high incidence of Bacteroides vulgatus (recovered in 80% of these mice), which can induce Th2-type responses of colonic CD4(+), betabeta T cells. In contrast, ED-fed TCR alpha(-/-) mice exhibited a diversification of Vbeta usage of betabetaT cell populations from the dominant Vbeta8 one associated with B. vulgatus in cecal flora to Vbeta6, Vbeta11, and Vbeta14. Rectal administration of disease-free ED-fed mice with B. vulgatus resulted in the development of Th2-type CD4(+), betabeta T cell-induced colitis. These findings suggest that the ED-induced alteration of intestinal microenvironments such as the enteric flora prevented the development of IBD in TCR alpha(-/-) mice via the immunologic quiescence of CD4(+), betabeta T cells.     

Constitutive TL1A (TNFSF15) expression on lymphoid or myeloid cells leads to mild intestinal inflammation and fibrosis

TL1A is a member of the TNF superfamily and its expression is increased in the mucosa of inflammatory bowel disease patients. Moreover, a subset of Crohn's disease (CD) patients with the risk TL1A haplotype is associated with elevated TL1A expression and a more severe disease course. To investigate the in vivo role of elevated TL1A expression, we generated two transgenic (Tg) murine models with constitutive Tl1a expression in either lymphoid or myeloid cells. Compared to wildtype (WT) mice, constitutive expression of Tl1a in either lymphoid or myeloid cells showed mild patchy inflammation in the small intestine, which was more prominent in the ileum. In addition, mice with constitutive Tl1a expression exhibited enhanced intestinal and colonic fibrosis compared to WT littermates. The percentage of T cells expressing the gut homing chemokine receptors CCR9 and CCR10 was higher in the Tl1a Tg mice compared to WT littermates. Sustained expression of Tl1A in T cells also lead to increased Foxp3+ Treg cells. T cells or antigen presenting cells (APC) with constitutive expression of Tl1a were found to have a more activated phenotype and mucosal mononuclear cells exhibit enhanced Th1 cytokine activity. These results indicated an important role of TL1A in mucosal T cells and APC function and showed that up-regulation of TL1A expression can promote mucosal inflammation and gut fibrosis.     

Commensal bacteria exacerbate intestinal inflammation but are not essential for the development of murine ileitis

The pathogenesis of Crohn's disease has been associated with a dysregulated response of the mucosal immune system against intraluminal Ags of bacterial origin. In this study, we have investigated the effects of germfree (GF) conditions in the SAMP1/YitFc murine model of Crohn's disease-like ileitis. We show that the bacterial flora is not essential for ileitis induction, because GF SAMP1/YitFc mice develop chronic ileitis. However, compared with disease in specific pathogen-free (SPF) mice, ileitis in GF mice is significantly attenuated, and is associated with delayed lymphocytic infiltration and defective mucosal expression of Th2 cytokines. In addition, we demonstrate that stimulation with purified fecal Ags from SPF, but not GF mice leads to the generation of IL-4-secreting effector lymphocytes. This result suggests that commensal bacteria drive Th2 responses characteristic of the chronic phase of SAMP1/YitFc ileitis. Finally, adoptive transfer of CD4-positive cells from GF, but not SPF mice induces severe colitis in SCID recipients. These effects were associated with a decreased frequency of CD4(+)CD25(+)Foxp3(+) T cells in the mesenteric lymph nodes of GF mice compared with SPF mice, as well as lower relative gene expression of Foxp3 in CD4(+)CD25(+) T cells in GF mice. It is therefore apparent that, in the absence of live intraluminal bacteria, the regulatory component of the mucosal immune system is compromised. All together, our results indicate that in SAMP1/YitFc mice, bacterial flora exacerbates intestinal inflammation, but is not essential for the generation of the chronic ileitis that is characteristic of these mice.     

Osteopontin as two-sided mediator of intestinal inflammation

Osteopontin (OPN) is characterized as a major amplifier of Th1-immune responses. However, its role in intestinal inflammation is currently unknown. We found considerably raised OPN levels in blood of wild-type (WT) mice with dextran sodium sulfate (DSS)-induced colitis. To identify the role of this mediator in intestinal inflammation, we analysed experimental colitis in OPN-deficient (OPN(-/-)) mice. In the acute phase of colitis these mice showed more extensive colonic ulcerations and mucosal destruction than WT mice, which was abrogated by application of soluble OPN. Within the OPN(-/-) mice, infiltrating macrophages were not activated and showed impaired phagocytosis. Reduced mRNA expression of interleukin (IL)-1 beta and matrix metalloproteinases was found in acute colitis of OPN(-/-) mice. This was associated with decreased blood levels of IL-22, a Th17 cytokine that may mediate epithelial regeneration. However, OPN-(/-) mice showed increased serum levels of tumour necrosis factor (TNF)-alpha, which could be due to systemically present lipopolysaccharide translocated to the gut. In contrast to acute colitis, during chronic DSS-colitis, which is driven by a Th1 response of the lamina propria infiltrates, OPN(-/-) mice were protected from mucosal inflammation and demonstrated lower serum levels of IL-12 than WT mice. Furthermore, neutralization of OPN in WT mice abrogated colitis. Lastly, we demonstrate that in patients with active Crohn's disease OPN serum concentration correlated significantly with disease activity. Taken together, we postulate a dual function of OPN in intestinal inflammation: During acute inflammation OPN seems to activate innate immunity, reduces tissue damage and initiates mucosal repair whereas during chronic inflammation it promotes the Th1 response and strengthens inflammation.     

Transient local depletion of Foxp3+ regulatory T cells during recovery from colitis via Fas/Fas ligand-induced death

Regulatory T cells (Tregs) play a fundamental role in regulating the immune system in health and disease. Considerable evidence exists demonstrating that transfer of Tregs can cure colitis and a variety of other inflammatory disorders. However, little is known about the effects of inflammation on resident Tregs. Mice (BALB/c or C57BL/6) treated with an intrarectal instillation of the haptenizing agent 2,4-dinitrobenzene sulfonic acid (DNBS) develop an acute inflammatory disease, the histopathology of which peaks at 3 days posttreatment and resolves spontaneously thereafter. In this study we demonstrate that DNBS (or oxazolone)-induced colitis causes a depletion of colonic Foxp3+ Tregs 8 days posttreatment, while the proportion of Foxp3+ cells in the ileum, mesenteric lymph nodes, and spleen remains unchanged. Replenishment of the colonic Treg population was associated with the reappearance of mucosal homing (alpha4beta7+) CD4+Foxp3+ Tregs. Assessing the mechanism of local Treg depletion, we found no evidence to implicate cytokine-induced phenotypic switching in the Foxp3+ population or increased SMAD7 expression despite the essential role that TGF-beta has in Foxp3+ Treg biology. Increased Fas ligand (FasL) expression was observed in the colon of colitic mice and in vitro stimulation with a Fas cross-linking Ab resulted in apoptosis of CD4+Foxp3+ but not CD4+Foxp3- cells. Furthermore, DNBS-induced colitis in Fas/FasL-deficient mice did not result in depletion of colonic Tregs. Finally, adoptively transferred synergic Fas-/- but not Fas+/+ Tregs were protected from depletion in the colon 8 days post-DNBS treatment, thus substantiating the hypothesis that inflammation-induced local depletion of Foxp3+ Tregs in the colon of mice occurs via Fas/FasL-mediated death.     

The susceptibility to experimental myasthenia gravis of STAT6-/- and STAT4-/- BALB/c mice suggests a pathogenic role of Th1 cells

Autoantibodies to the muscle acetylcholine receptor (AChR) cause the symptoms of human and experimental myasthenia gravis (EMG). AChR-specific CD4+ T cells permit development of these diseases, but the role(s) of the Th1 and Th2 subsets is unclear. The STAT4 and STAT6 proteins, which mediate intracellular cytokine signaling, are important for differentiation of Th1 and Th2 cells, respectively. Wild-type (WT) BALB/c mice, which are prone to develop Th2 rather than Th1 responses to Ag, are resistant to EMG. We have examined the role of Th1 and Th2 cells in EMG using STAT4 (STAT4-/-)- or STAT6 (STAT6-/-)-deficient BALB/c mice. After AChR immunization, STAT6-/- mice were susceptible to EMG: they developed more serum anti-AChR Ab, and had more complement-fixing anti-AChR IgG2a and 2b and less IgG1 than WT or STAT4-/- mice. The susceptibility to EMG of STAT6-/- mice is most likely related to the Th1 cell-induced synthesis of anti-AChR Ab, which trigger complement-mediated destruction of the neuromuscular junction. CD4+ T cells of the STAT6-/- mice had proliferative responses to the AChR comparable to those of WT and STAT4-/- mice, and recognized similar AChR epitopes. STAT6-/- mice had abundant AChR-specific Th1 cells, which were nearly absent in WT and STAT4-/- mice. Spleen and lymph nodes from STAT6-/- mice contained cells that secreted IL-4 when cultured with AChR: these are most likely STAT6-independent cells, stimulated in a non-Ag-specific manner by the cytokines secreted by AChR-specific Th1 cells.     

Mucosal T lymphocyte numbers are selectively reduced in integrin alpha E (CD103)-deficient mice.

The mucosal lymphocyte integrin alpha E(CD103)beta 7 is thought to be important for intraepithelial lymphocyte (IEL) localization or function. We cloned the murine integrin gene encoding alpha E, localized it to chromosome 11, and generated integrin alpha E-deficient mice. In alpha E-/- mice, intestinal and vaginal IEL numbers were reduced, consistent with the known binding of alpha E beta 7 to E-cadherin expressed on epithelial cells. However, it was surprising that lamina propria T lymphocyte numbers were diminished, as E-cadherin is not expressed in the lamina propria. In contrast, peribronchial, intrapulmonary, Peyer's patch, and splenic T lymphocyte numbers were not reduced in alpha E-deficient mice. Thus, alpha E beta 7 was important for generating or maintaining the gut and vaginal T lymphocytes located diffusely within the epithelium or lamina propria but not for generating the gut-associated organized lymphoid tissues. Finally, the impact of alpha E deficiency upon intestinal IEL numbers was greater at 3-4 wk of life than in younger animals, and affected the TCR alpha beta+ CD8+ T cells more than the gamma delta T cells or the TCR alpha beta+ CD4+CD8- population. These findings suggest that alpha E beta 7 is involved in the expansion/recruitment of TCR alpha beta+ CD8+ IEL following microbial colonization. Integrin alpha E-deficient mice will provide an important tool for studying the role of alpha E beta 7 and of alpha E beta 7-expressing mucosal T lymphocytes in vivo.