Development of inflammatory bowel disease in Long-Evans Cinnamon rats based on CD4+CD25+Foxp3+ regulatory T cell dysfunction

Research progress of ferroptosis and inflammatory bowel disease

Inflammatory bowel disease (IBD) is a non-specific chronic inflammatory disorder of the gastrointestinal tract, imposing significant burdens on both society and individuals. As a new type of regulated cell death (RCD), ferroptosis is different from classic RCDs such as apoptosis and necrosis in cell morphology, biochemistry and genetics. The main molecular mechanisms of ferroptosis include dysregulation of iron metabolism, impaired antioxidant capacity, mitochondrial dysfunction, accumulation of lipid-associated super-oxides, and membrane disruption. In recent years, increasing evidence has shown that ferroptosis is involved in the pathophysiology of inflammatory bowel disease. However, the exact roles and underlying molecular mechanisms have not been fully elucidated. This article reviews the mechanism of ferroptosis in the occurrence and development of inflammatory bowel disease, in order to provide new ideas for the pathophysiological research of inflammatory bowel disease. Additionally, we discuss potential strategies for the prevention and treatment of inflammatory bowel disease by targeting ferroptosis.

Melatonin and inflammatory bowel disease: From basic mechanisms to clinical application

Inflammatory bowel disease is a chronic inflammatory disease and has periods of recurrence and remission. Improper immune responses to gut flora bacteria, along with genetic susceptibility, appear to be involved in causing this complex disease. It seems dysbiosis and oxidative stress may also be involved in IBD pathogenesis. A significant number of clinical studies have shown an interesting association between sleep disturbances and IBD. Studies in animal models have also shown that sleep deprivation has a significant effect on the pathogenesis of IBD and can aggravate inflammation. These interesting findings have drawn attention to melatonin, a sleep-related hormone. Melatonin is mainly produced by the pineal gland, but many tissues in the body, including the intestines, can produce it. Melatonin can have an interesting effect on the pathogenesis of IBD. Melatonin can enhance the intestinal mucosal barrier, alter the composition of intestinal bacteria in favor of bacteria with anti-inflammatory properties, regulate the immune response, alleviate inflammation and attenuate oxidative stress. It seems that, melatonin supplementation is effective in relieving inflammation and healing intestinal ulcers in IBD animal models. Some clinical studies have also shown that melatonin supplementation as an adjuvant therapy may be helpful in reducing disease activity in IBD patients. In this review article, in addition to reviewing the effects of sleep disturbances and melatonin on key mechanisms involved in the pathogenesis of IBD, we will review the findings of clinical studies regarding the effects of melatonin supplementation on IBD treatment.

The role of diosgenin in crohn’s disease

Inflammatory bowel disease (IBD) is a chronic idiopathic inflammation that can grossly affect the entire gastrointestinal tract (GIT) from the mouth to the anus. Crohn’s disease is the most known type of IBD and has been the focus of attention due to its increase in prevalence worldwide. Although the etiology is yet to be elucidated, recent studies have pointed out Crohn’s disease to arise from a complex interaction between environmental influences, genetic predisposition, and altered gut microbiota, resulting in dysregulated adaptive and innate responses. The presenting hallmarks of Crohn’s disease may include weight loss, nausea, vomiting, abdominal pain, diarrhea, fever, or chills. Treatment is usually done with many approved immunosuppressive drugs and surgery. However, a promising avenue from natural compounds is a safer therapy due to its safe natural active ingredients and the strong activity it shows in the treatment and management of diseases. Diosgenin, “a major biologically active natural steroidal sapogenin found in Chinese yam,” has been widely reported as a therapeutic agent in the treatment of various classes of disorders such as hyperlipidemia, inflammation, diabetes, cancer, infection, and immunoregulation. In this review, an analysis of literature data on diosgenin employed as a therapeutic agent for the treatment of Crohn’s disease is approached, to strengthen the scientific database and curtail the dreadful impact of Crohn’s disease.

Mevalonate promotes differentiation of regulatory T cells

Mevalonate is a precursor in a biosynthetic pathway that is important for the coordination of regulatory T cell (Treg) proliferation and upregulation of the suppressive function that establishes the functional competency of Tregs. The extensive role of mevalonate and its underlying effect on Treg differentiation are still unclear. We found that mevalonate increases in vitro differentiation of induced Tregs (iTregs) without broadly affecting Th1 and Th17 cell differentiation. Furthermore, an adoptive transfer study showed that mevalonate enhanced peripherally induced Treg cells (pTregs) in mesenteric lymphocytes in vivo. Mevalonate-treated iTregs exhibited greater suppressive activity against effector cells than untreated Tregs. Mechanistically, mevalonate enhanced transforming growth factor (TGF)-β signaling by increasing the phosphorylation of Smad3, but not Smad2, and by promoting Foxp3 expression. Furthermore, we demonstrated that mevalonate treatment ameliorated dextran sulfate sodium (DSS)-induced colitis and resulted in an increased percentage of Tregs in vivo. Our results suggest that mevalonate enhanced Treg differentiation and ameliorated DSS colitis, indicating its potential for treatment of inflammatory diseases.

Therapeutic potential of hepatocyte-like-cells converted from stem cells from human exfoliated deciduous teeth in fulminant Wilson's disease

Wilson’s disease (WD) is an inherited metabolic disease arising from ATPase copper transporting beta gene (ATP7B) mutation. Orthotoropic liver transplantation is the only radical treatment of fulminant WD, although appropriate donors are lacking at the onset of emergency. Given the hepatogenic capacity and tissue-integration/reconstruction ability in the liver of stem cells from human exfoliated deciduous teeth (SHED), SHED have been proposed as a source for curing liver diseases. We hypothesized the therapeutic potential of SHED and SHED-converted hepatocyte-like- cells (SHED-Heps) for fulminant WD. SHED and SHED-Heps were transplanted into WD model Atp7b-mutated Long-Evans Cinnamon (LEC) rats received copper overloading to induce a lethal fulminant liver failure. Due to the superior copper tolerance via ATP7B, SHED-Hep transplantation gave more prolonged life-span of fulminant LEC rats than SHED transplantation. The integrated ATP7B-expressing SHED-Heps showed more therapeutic effects on to restoring the hepatic dysfunction and tissue damages in the recipient liver than the integrated naïve SHED without ATP7B expression. Moreover, SHED-Heps could reduce copper-induced oxidative stress via ATP7B- independent stanniocalcin 1 secretion in the fulminant LEC rats, suggesting a possible role for paracrine effect of the integrated SHED-Heps. Taken together, SHED-Heps offer a potential of functional restoring, bridging, and preventive approaches for treating fulminant WD.

Mesenchymal stem cell expression of interleukin-35 protects against ulcerative colitis by suppressing mucosal immune responses

BACKGROUND

Interleukin-35 (IL-35) has recently been identified as an immunosuppressive cytokine that has been used as a potential therapy for chronic inflammatory and autoimmune diseases. However, there remains a paucity of data regarding its potential benefits after integration into mesenchymal stem cells (MSCs).

METHODS

We used a dextran sulfate sodium (DSS)-induced colitis mice model and treated them with IL-35-MSCs, MSCs or saline. The body weight was recorded daily and inflammatory processes were determined. Cytokine secretion by lamina propria lymphocytes (LPLs) and percentage of regulatory T cells (Tregs) were also measured.

RESULTS

The data showed that mice in the two treated groups recovered their body weight more rapidly than mice treated with saline in the later stage of colitis. The colon lengths of IL-35-MSC-treated mice were markedly longer than those in the other two groups and the inflammation reduced significantly. Furthermore, the percentage of Foxp3 + Tregs increased significantly and the level of proinflammatory cytokines produced by LPLs decreased significantly in the IL-35-MSC-treated group.

DISCUSSION

The results demonstrate that IL-35-MSCs could ameliorate ulcerative colitis by down-regulating the expression of pro-inflammatory cytokines.

Immunomodulatory effect of CD200-positive human placenta-derived stem cells in the early phase of stroke

Human placenta amniotic membrane-derived mesenchymal stem cells (AMSCs) regulate immune responses, and this property can be exploited to treat stroke patients via cell therapy. We investigated the expression profile of AMSCs cultured under hypoxic conditions and observed interesting expression changes in various genes involved in immune regulation. CD200, an anti-inflammatory factor and positive regulator of TGF-β, was more highly expressed under hypoxic conditions than normoxic conditions. Furthermore, AMSCs exhibited inhibition of pro-inflammatory cytokine expression in co-cultures with LPS-primed BV2 microglia, and this effect was decreased in CD200-silenced AMSCs. The AMSCs transplanted into the ischemic rat model of stroke dramatically inhibited the expression of pro-inflammatory cytokines and up-regulated CD200, as compared with the levels in the sham-treated group. Moreover, decreased microglia activation in the boundary region and improvements in behavior were confirmed in AMSC-treated ischemic rats. The results suggested that the highly expressed CD200 from the AMSCs in a hypoxic environment modulates levels of inflammatory cytokines and microglial activation, thus increasing the therapeutic recovery potential after hypoxic-ischemic brain injury, and further demonstrated the immunomodulatory function of AMSCs in a stroke model.

A Novel Role for TL1A/DR3 in Protection against Intestinal Injury and Infection

TNF-like cytokine 1A (TL1A) is expressed on APCs and provides costimulatory signals to activated lymphocytes that bear its functional receptor, death receptor 3 (DR3). TL1A/DR3 signaling is involved in the pathogenesis of human and experimental inflammatory bowel disease. In the current study, we investigated the role of this cytokine/receptor pair in acute intestinal injury/repair pathways. We demonstrate that intact DR3 signaling protected mice from acute dextran sodium sulfate colitis because DR3(-/-) mice showed more severe mucosal inflammation and increased mortality. DR3(-/-) mice were compromised in their ability to maintain adequate numbers of CD4(+)CD25(+)Foxp3(+) regulatory T cells in response to acute mucosal damage. This defect in immune regulation led to a nonspecific upregulation of effector proinflammatory pathways, which was most prominent for the Th17 immunophenotype. TL1A(-/-) mice were similarly more susceptible to dextran sodium sulfate colitis, although without mortality and with delayed kinetics compared with DR3(-/-) mice, and also displayed significantly reduced numbers of regulatory T cells. Infection of DR3(-/-) mice with Salmonella typhimurium was associated with defective microbial clearance and elevated bacterial load. Taken together, our findings indicate a novel protective role for the TL1A/DR3 axis in the regulation of mucosal homeostasis during acute intestinal injury/repair, which contrasts with its known pathogenic function during chronic intestinal inflammation.

Role of regulatory T cell in the pathogenesis of inflammatory bowel disease

Regulatory T (Treg) cells play key roles in various immune responses. For example, Treg cells contribute to the complex pathogenesis of inflammatory bowel disease (IBD), which includes Crohn's disease and ulcerative colitis during onset or development of that disease. Many animal models of IBD have been used to investigate factors such as pathogenic cytokines, pathogenic bacteria, and T-cell functions, including those of Treg cells. In addition, analyses of patients with IBD facilitate our understanding of the precise mechanism of IBD. This review article focuses on the role of Treg cells and outlines the pathogenesis and therapeutic strategies of IBD based on previous reports.

A potential role for regulatory T-cells in the amelioration of DSS induced colitis by dietary non-digestible polysaccharides

Inflammatory bowel diseases (IBD) including ulcerative colitis (UC) and Crohn's disease (CD) are chronic relapsing inflammatory disorders of the gastrointestinal tract. The interaction between a disturbed microbial composition, the intestinal mucosal barrier and the mucosal immune system plays an important role in IBD and its chronicity. It has been indicated that due to the altered microbial composition the balance between T regulatory cells (Treg) and T helper cells (Th) 17 is disturbed, leading to an inflammatory state. The present study shows that oral intake of a specific multi fibre mix (MF), designed to match the fibre content of a healthy diet, counteracts IBD-like intestinal inflammation and weight loss in dextran sodium sulphate treated mice. This reduction in inflammation might be brought about, at least in part, by the MF-induced decrease in inflammatory cytokines, increase in IL-10 and the relative increase in Treg cells in the mesenteric lymph nodes (MLN). Moreover, the Treg percentage in the MLN correlates with the percentage of tolerogenic lamina propria derived CD103+RALDH+dendritic cells in the MLN, suggesting that these play a role in the observed effects. In children with CD exclusive enteral nutrition (EEN) is a widely used safe and effective therapy. Optimizing enteral nutritional concepts with the tested fibre mix, know to modulate the gut microbiota composition, SCFA production and inflammatory status (as indicated by the present study) could possibly further improve efficacy in inducing remission.

Thymic epithelial cell development and its dysfunction in human diseases

Thymic epithelial cells (TECs) are the key components in thymic microenvironment for T cells development. TECs, composed of cortical and medullary TECs, are derived from a common bipotent progenitor and undergo a stepwise development controlled by multiple levels of signals to be functionally mature for supporting thymocyte development. Tumor necrosis factor receptor (TNFR) family members including the receptor activator for NFκB (RANK), CD40, and lymphotoxin β receptor (LTβR) cooperatively control the thymic medullary microenvironment and self-tolerance establishment. In addition, fibroblast growth factors (FGFs), Wnt, and Notch signals are essential for establishment of functional thymic microenvironment. Transcription factors Foxn1 and autoimmune regulator (Aire) are powerful modulators of TEC development, differentiation, and self-tolerance. Dysfunction in thymic microenvironment including defects of TEC and thymocyte development would cause physiological disorders such as tumor, infectious diseases, and autoimmune diseases. In the present review, we will summarize our current understanding on TEC development and the underlying molecular signals pathways and the involvement of thymus dysfunction in human diseases.

Keeping the bowel regular: the emerging role of Treg as a therapeutic target in inflammatory bowel disease

The understanding of the intricate mechanisms by which gut immune cells interact with each other and the intestinal flora is constantly developing. The mucosal immune system must retain the ability to mount a prompt response to intestinal pathogens while maintaining tolerance for commensal organisms. Effector T lymphocytes drive inflammation, whereas their actions are counteracted by populations of regulatory T cells (Treg), which act as an endogenous suppressor of mucosal inflammation. There is growing evidence that a loss of this delicate counterbalance is important in the etiology of inflammatory bowel disease (IBD). Here, we review studies highlighting alterations in Treg in the pathogenesis of IBD. Observations of dynamic changes in Treg activity with successful IBD treatment have highlighted their functional importance and potential to also serve as a biomarker of disease activity and to predict response to therapy. Furthermore, we explore the potential for adoptive transfer of Treg as part of IBD treatment.

Adoptive regulatory T-cell therapy protects against cerebral ischemia

OBJECTIVE

Recent evidence suggests that functional deficiency in regulatory T cells (Tregs), an innate immunomodulator, exacerbates brain damage after cerebral ischemia. We therefore evaluated the effect of Treg transfer in rodent models of ischemic stroke and further investigated the mechanism underlying Treg-afforded neuroprotection.

METHODS

We examined the therapeutic potential of Tregs and the mechanisms of neuroprotection in vivo in 2 rodent models of ischemic stroke and in vitro in Treg-neutrophil cocultures using a combined approach including cell-specific depletion, gene knockout mice, and bone marrow chimeras.

RESULTS

Systemic administration of purified Tregs at 2, 6, or even 24 hours after middle cerebral artery occlusion resulted in a marked reduction of brain infarct and prolonged improvement of neurological functions lasting out to 4 weeks. Treg-afforded neuroprotection was accompanied by attenuated blood-brain barrier (BBB) disruption during early stages of ischemia, decreased cerebral inflammation, and reduced infiltration of peripheral inflammatory cells into the lesioned brain. Surprisingly, Tregs exerted early neuroprotection without penetrating into the brain parenchyma or inhibiting the activation of residential microglia. Rather, both in vivo and in vitro studies demonstrated that Tregs suppressed peripheral neutrophil-derived matrix metallopeptidase-9 production, thus preventing proteolytic damage of the BBB. In addition to its potent central neuroprotection, Treg treatment was shown to ameliorate poststroke lymphopenia, suggesting a beneficial effect on immune status.

INTERPRETATION

Our study suggests that Treg adoptive therapy is a novel and potent cell-based therapy targeting poststroke inflammatory dysregulation and neurovascular disruption.

Tregs are dysfunctional in vivo in a spontaneous murine model of Crohn's disease

Although regulatory T cells (Tregs) have been implicated in inflammatory bowel disease, Tregs from Crohn's disease (CD) patients are increased in number and function normally in vitro. To clarify this disparity, we studied Treg function in vivo using a spontaneous model of CD-like ileitis. We first administered anti-CD25-depleting antibodies to SAMP1/YitFc (SAMP) mice to assess ileitis; mesenteric lymph node cells were then transferred into SCID (severe combined immunodeficient) recipients to induce colitis. CD25 depletion increased the severity of both spontaneous ileitis and adoptively transferred colitis. Interestingly, a second transfer of CD4(+)CD25(+) cells from untreated AKR control mice was able to ameliorate the induced colitis, whereas CD4(+)CD25(+) cells from untreated SAMP mice were not, suggesting a functional abnormality in SAMP Tregs. Anti-CD25 treatment in SAMP mice also induced proliferation of CD25(-)Foxp3(+) Tregs, which had a proinflammatory intestinal T helper type 1/ T helper type 2 (Th1/Th2) effector phenotype. These studies demonstrate Treg dysfunction in a spontaneous model of CD-like ileitis.

Immunohistochemical investigation of Foxp3 expression in the intestine in healthy and diseased dogs

Intestinal immune regulation including development of oral tolerance is of great importance for the maintenance of intestinal homeostasis. Concerning this, regulatory T cells (Tregs) occupy a pivotal role in cell-mediated immunosuppression. Dysregulation of mucosal immunology leading to an abnormal interaction with commensal bacteria is suggested to play a key role in the pathogenesis of Inflammatory Bowel Disease (IBD) in men and dogs. The aim of this study was to characterise the expression of Foxp3 in the normal canine gut of 18 dogs (mean age: 6.03 years), in 16 dogs suffering from IBD (mean age: 5.05 years), and of 6 dogs with intestinal nematode infection (mean age: 0.87 years) using immunohistochemistry. In the duodenum, Tregs in healthy dogs declined from villi (median: 10.67/62 500 μm2) to crypts (median: 1.89/62 500 μm2). Tregs were further increased in the villi of middle-aged dogs (median: 18.92/62 500 μm2) in contrast to juvenile (median: 3.50/62 500 μm2) and old (median: 9.56/62 500 μm2) individuals. Compared to healthy controls, animals suffering from IBD revealed reduced numbers of Tregs in duodenal villi (median: 4.13/62 500 μm2). Dogs with intestinal nematode infection displayed increased numbers of Tregs (median: 21.06/62 500 μm2) compared to healthy animals.Age-related changes indicate a progressive establishment of oral tolerance and immunosenescence in the canine elderly. The results further suggest that a defect in Treg homeostasis may be involved in the pathogenesis of canine IBD. In contrast, increased numbers of Tregs in the duodenum may be due to nematode infection.

The effects of Foxp3-expressing regulatory T cells expanded with CD28 superagonist antibody in DSS-induced mice colitis

Regulatory T (Treg) cells play an important role in the pathogenesis of inflammatory bowel disease (IBD). In the present study, we found that a superagonistic CD28-specific monoclonal antibody (supCD28mAb, D665) could preferentially stimulate expansion of CD4+Foxp3+ Treg cells. Foxp3(EGFP) mice were orally administrated with 3.5% DSS for 5days, and intraperitoneally injected supCD28mAb 1mg/mice in treated group. All of the mice were sacrificed on day 8, and both clinical and histological parameters showed that the severity of colitis was significantly reduced in treated group compared to controls. In treated group, the proportion of CD103, CD152 and CD62L expression on Foxp3+Treg cells in the spleen and mesenteric lymph node were higher than controls. Furthermore, qRT-PCR analysis showed that expression of anti-inflammatory cytokines such as IL-10, TGF-β was significantly increased in treated group. Taken together, our data demonstrated that supCD28mAb targets CD4+Foxp3+Treg cells expansion in vivo, maintains and enhances their regulatory functions, to reduce the damage of colon in dextran sulfate sodium (DSS)-induced mouse colitis by secreting a large amount of IL-10. It represents a major advance towards the therapeutic use of polyclonally activated Treg cells as cellular therapy for treatment of IBD.

Th17 and regulatory T cells: implications for AIDS pathogenesis

PURPOSE OF REVIEW

The present review discusses recent reports showing that reciprocal changes in T helper interleukin-17-secreting CD4 Th17 cells and CD4CD25FoxP3 regulatory T cells (Tregs) may play a role in the progressive disease caused by the HIV and by simian immunodeficiency virus.

RECENT FINDINGS

Studies in nonhuman primate models of lentiviral infection and in HIV-infected human individuals have shown that pathogenic infection is associated with loss of Th17 cells and an increase in the frequency of Tregs. Because interleukin-17 serves to maintain the integrity of the mucosal barrier, loss of Th17 cells may permit the increase in microbial translocation across the gastrointestinal mucosa that is observed in pathogenic lentiviral disease. It remains unclear, however, whether Th17 cells are preferentially infected or if, instead, their loss is induced by bystander effects of lentiviral infection, for example, the induction of indoleamine 2,3-dioxygenase.

SUMMARY

Progressive lentiviral disease is associated with preferential depletion of Th17 cells and loss of Th17/Treg balance. Further analysis of such changes in the composition of subset CD4 T helper and Tregs may shed new light on the immunopathology of HIV disease and suggest new strategies for therapeutic and preventive interventions.

In situ patrolling of regulatory T cells is essential for protecting autoimmune exocrinopathy

BACKGROUND

Migration of T cells, including regulatory T (Treg) cells, into the secondary lymph organs is critically controlled by chemokines and adhesion molecules. However, the mechanisms by which Treg cells regulate organ-specific autoimmunity via these molecules remain unclear. Although we previously reported autoimmune exocrinopathy resembling Sjögren's syndrome (SS) in the lacrimal and salivary glands from C-C chemokine receptor 7 (CCR7)-deficient mice, it is still unclear whether CCR7 signaling might specifically affect the dynamics and functions of Treg cells in vivo. We therefore investigated the cellular mechanism for suppressive function of Treg cells via CCR7 in autoimmunity using mouse models and human samples.

METHODS AND FINDINGS

Patrolling Treg cells were detected in the exocrine organs such as lacrimal and salivary glands from normal mice that tend to be targets for autoimmunity while the Treg cells were almost undetectable in the exocrine glands of CCR7(-/-) mice. In addition, we found the significantly increased retention of CD4(+)CD25(+)Foxp3(+) Treg cells in the lymph nodes of CCR7(-/-) mice with aging. Although Treg cell egress requires sphingosine 1-phosphate (S1P), chemotactic function to S1P of CCR7-/- Treg cells was impaired compared with that of WT Treg cells. Moreover, the in vivo suppression activity was remarkably diminished in CCR7(-/-) Treg cells in the model where Treg cells were co-transferred with CCR7(-/-) CD25(-)CD4(+) T cells into Rag2(-/-) mice. Finally, confocal analysis showed that CCR7(+)Treg cells were detectable in normal salivary glands while the number of CCR7(+)Treg cells was extremely decreased in the tissues from patients with Sjögren's syndrome.

CONCLUSIONS

These results indicate that CCR7 essentially governs the patrolling functions of Treg cells by controlling the traffic to the exocrine organs for protecting autoimmunity. Characterization of this cellular mechanism could have clinical implications by supporting development of new diagnosis or treatments for the organ-specific autoimmune diseases such as Sjögren's syndrome and clarifying how the local immune system regulates autoimmunity.

Long-term treatment of NZB mice with anti-CD4 results in wasting disease, lymphoid atrophy and chronic diarrhea

In this paper, we have shown that long-term treatment of NZB mice with anti-CD4 antibody results in four major pathological effects: firstly the development of a severe wasting disease; secondly lymphoid atrophy of the thymus, spleen, mesenteric lymph node and Peyers patches (PP); thirdly, severe chronic ulcerative colitis and fourthly a neutrophilia with neutrophil infiltration in the spleen, liver and mesenteric lymph nodes. At the same time, mice subjected to anti-CD4 treatment showed a reduction in the microbial diversity in ileal walls and contents, as well as in colonic contents, together with overgrowth of E. coli in the intestinal lumen and wall. In addition, there was the appearance of large numbers of spiral shaped bacteria on the mucosal surface often associated with colonic ulceration.

Low susceptibility to N-ethyl-N-nitrosourea-induced transplacental carcinogenesis in Long-Evans Cinnamon (LEC) rats

The Long-Evans Cinnamon (LEC) rat, an animal model of Wilson's disease, is resistant to a variety of chemical carcinogenesis except liver and colon. In the present study, N-ethyl-N-nitrosourea (ENU)-induced transplacental carcinogenesis was examined in male and female LEC, Long-Evans Agouti (LEA), a sibling line of the LEC rat, and F344 rats (n=21). ENU was administered to pregnant rats as a single s.c. injection at a dose of 60 mg/kg body weight on the 17th day after conception. Cerebral/spinal gliomas and trigeminal/spinal nerve schwannomas developed in both LEA and F344 rats at 30 weeks of age, but no nervous system tumors developed in LEC rats, the difference being statistically significant. Lung adenomas also developed in LEA and F344 rats, but not in LEC rats. Semiquantitative RT-PCR demonstrated that metallothionein (MT)1a, MT2 and O(6)-methylguanine-DNA methyltransferase (MGMT) mRNA levels in the liver of LEC rats were higher than those in F344 and LEA rats. In addition, Western blot analysis showed that MT (MT1 plus MT2) in the liver of LEC rats was also higher than that in other strains. Present results suggest that high levels of MT and/or MGMT contribute to the resistance to nitrosamine-induced carcinogenesis in LEC rats.