旋毛虫对三硝基苯磺酸诱导的实验性小鼠肠炎模型的干预研究

目的 研究旋毛虫对三硝基苯磺酸（TNBS）诱导的实验性小鼠肠炎模型的影响及其免疫作用机制。方法观察感染和未感染旋毛虫小鼠于TNBS诱导肠炎后3d及7d不同指标的变化，包括小鼠生存率、疾病活动指数（DAI）、结肠大体损伤和病理损伤评分、炎症指标髓过氧化物酶（MPO）活性检测，结肠细胞因子IFN-γ和IL-4 mRNA的表达量分析。结果 预先感染旋毛虫后诱导TNBS模型组小鼠在造模后3d及7d与单纯模型组相比小鼠生存率升高（P〈0．05），DAI、结肠大体损伤和病理损伤评分及MPO活性下降（P〈0．05），结肠中IFN-γmRNA的表达量下调（P〈0．05），而IL-4 mRNA的表达量增加（P〈0．05）。结论 旋毛虫对TNBS诱导的实验性小鼠肠炎具有良好的干预作用，其免疫作用机制可能是通过下调炎症性肠病过度的．TH1型免疫反应、上调TH2型免疫反应而实现的。     

旋毛虫对三硝基苯磺酸和噁唑酮诱导肠炎小鼠结肠中Th1/Th2类细胞因子表达的影响

目的 研究旋毛虫(T. spiralis)对三硝基苯磺酸(TNBS)和噁唑酮(OXZ)诱导的实验性肠炎小鼠结肠中Th1/Th2类细胞因子表达的影响.方法 雌性BALB/c小鼠,随机分为50%乙醇对照组、T. spiralis应用组、TNBS(OXZ)诱导肠炎模型组、预先感染T. spiralis后诱导TNBS(OXZ)模型组(每组小鼠取材时保证6只以上).对各组小鼠肠黏膜固有层单个核细胞(LPMC)进行分离培养,采用ELISA方法观察感染T.spiralis和未感染T.spiralis小鼠于TNBS或OXZ诱导肠炎后3 d和7 d结肠中Th1/Th2类细胞因子蛋白的表达变化,包括IFN-γ、IL-12、IL-4、IL-10的表达量分析.结果 预先感染T. spiralis后诱导TNBS模型组小鼠在造模后3 d及7 d肠黏膜LPMC产生IFN-γ的水平均低于模型组(P＜0.05),而IL-4、IL-10的表达高于模型组(P＜0.05).预先感染T. spiralis后诱导TNBS模型组小鼠在造模后3 d肠黏膜LPMC产生IL-12的水平低于模型组(P＜0.05),第7天与模型组相比未见明显差异(P＞0.05).预先感染T. spiralis后诱导OXZ模型组小鼠在造模后3 d及7 d肠黏膜LPMC产生IFN-γ、IL-4及IL-10的水平均高于单纯造模组(P＜0.05).结论 T. spiralis对TNBS诱导的肠炎模型小鼠肠道局部免疫作用机制可能是通过诱导Th2型免疫反应及Tr1型细胞因子而抑制结肠炎小鼠Th1型过度免疫应答而实现的.在T.spiralis对OXZ模型小鼠的干预性研究中,没有按理论所设想的感染T.spiralis所产生的Th2型免疫反应会对OXZ诱导的Th2型炎症反应起叠加作用而加重病情.这提示我们,需要进一步探讨T.spiralis对拥有Th2型免疫应答的OXZ模型的具体作用机制.     

TNBS诱导结肠炎小鼠中细菌鞭毛蛋白的表达及其与肥大细胞脱颗粒的关系

目的:研究不同炎症程度下2,4,6-三硝基苯磺酸(TNBS)诱导的结肠炎小鼠的血清及结肠组织中细菌鞭毛蛋白CBir1的表达、肥大细胞脱颗粒的情况及两者的相关性。方法:将SPF级雄性BALB/c小鼠随机分为6组,每组12只,分别是:正常对照组、生理盐水组、50%乙醇组、50%乙醇+TNBS组、50%乙醇+TNBS+酮替芬组及50%乙醇+TNBS+脂多糖(LPS)+卵清蛋白(OVA)组,同时对小鼠进行疾病活动指数(DAI)评分。分组处理后第22天处死并提取小鼠的血清及结肠组织,采用组织损伤指数(HI)评分标准对小鼠结肠进行组织病理评估,采用ELISA法检测抗-CBir1、组胺以及肥大细胞类胰蛋白酶(MCT)在小鼠血清中的浓度,并用免疫组化法检测小鼠结肠组织中CBir1、Toll样蛋白受体5(TLR5)及MCT的表达。结果:TNBS诱导组的DAI评分和HI评分,且CBir1、TLR5、MCT、抗-CBir1和组胺在肠黏膜和血清中的表达明显高于正常对照组(P0.05);50%乙醇+TNBS组上述数值除TLR5外均低于50%乙醇+TNBS+LPS+OVA组(P0.05);50%乙醇+TNBS组上述数值除MCT外则均高于50%乙醇+TNBS+酮替芬组(P0.05);生理盐水和50%乙醇组小鼠与正常对照组小鼠比较,上述数值差异无统计学显著性。将TNBS诱导模型组小鼠血清中抗-CBir1与MCT的浓度进行相关性分析,结果提示两者呈正相关(r=0.751,P0.01);此外,小鼠的血清中抗-CBir1与组胺的浓度亦呈正相关(r=0.648,P0.01)。结论:TNBS诱导结肠炎炎症程度越重的小鼠,其体内CBir1的表达量越高,同时肥大细胞脱颗粒作用也越明显。TNBS诱导结肠炎小鼠体内CBir1的表达量与肥大细胞脱颗粒作用呈正相关性。     

Long-term study of TNBS-induced colitis in rats: Focus on mast cells

Objective and design To investigate the severity and duration of colitis induced by two different doses of 2,4,6-trinitrobenzenesulfonic acid (TNBS) and the changes in mast cell number in acute inflammation and in the recovery process of colitis. Methods Colitis was induced in rats by an enema of TNBS (10 or 30 mg) in 25% ethanol. Macroscopic and histologic changes of the colon, colon weight and mast cell counts were examined at various times (7, 30 and 60 days) after colitis induction. Results TNBS induced a colonic damage which was dose-related for both severity and time necessary to complete recovery. On day 7 after colitis induction 10 mg TNBS induced macroscopic and microscopic alterations of colonic architecture that completely resolved at day 60. By contrast, 30 mg TNBS induced massive necrosis, thickening of the colon, severe histologic changes that were only partially reversed after two months. Mast cell number in the submucosa and muscularis propria decreased significantly in the acute phase of inflammation (7 days) and slowly increased thereafter, reaching a maximum level (up to about 5-fold) at day 60 after both doses of TNBS. Conclusions Present data confirm the ability of TNBS to induce in rats damage to the colon that was dose-dependent for severity and duration. Moreover, these data unravel a different role of mast cells in TNBS-induced colitis: an early degranulation in the acute phase of inflammation and a subsequent accumulation of mast cells in the late phase of the disease, associated with tissue repair. Received 31 January 2006; returned for revision 29 April 2006; accepted by A. Falus 3 May 2006     

Predominant pathogenic role of tumor necrosis factor in experimental colitis in mice

Antibodies to tumor necrosis factor (TNF)-α have been recently proposed as effective treatment for patients with Crohn's disease. Here, we analyze the functional role of TNF-α in a mouse model of chronic intestinal inflammation induced by the hapten reagent 2,4,6,-trinitrobenzene sulfonic acid (TNBS) that mimics some characteristics of Crohn's disease in humans. Macrophage-enriched lamina propria (LP) mononuclear cells from mice with TNBS-induced colitis produced 10–30-fold higher levels of TNF-α mRNA and protein than cells from control mice. When mice with chronic colitis were treated by intraperitoneal injection of antibodies to TNF-α, an improvement of both the clinical and histopathologic signs of disease was found. Isolated macrophage-enriched LP cells from anti-TNF-α-treated mice produced strikingly less pro-inflammatory cytokines such as interleukin (IL)-1 and IL-6 in cell culture. The predominant role of TNF-α in the mouse TNBS-induced colitis model was further underlined by the finding that striking colonic inflammation and lethal pancolitis was induced in TNF-α-transgenic mice upon TNBS treatment. Conversely, no significant TNBS-induced colitis could be induced in mice in which the TNF-α gene had been inactivated by homologous recombination. Complementation of TNF-α function in TNF^?/? mice by the expression of a mouse TNF-α transgene was sufficient to reverse this effect. Taken together, the data provide direct evidence for a predominant role of TNF-α in a mouse model of chronic intestinal inflammation and encourage further clinical trials with antibodies to TNF-α for the treatment of patients with Crohn's disease.     

Tolerance towards resident intestinal flora in mice is abrogated in experimental colitis and restored by treatment with interleukin-10 or antibodies to interleukin-12

There is now increasing evidence that hyperresponsiveness towards intestinal flora is a crucial event in the pathogenesis of inflammatory bowel disease (IBD). In support of this hypothesis, we recently described in humans that tolerance exists towards indigenous intestinal flora but is broken in active IBD lesions. In the present study, we have attempted to transfer this model into mice from different genetic backgrounds (BALB/c, SJL/J, C3H/HeJ). We found that mononuclear cells from spleen, small bowel and large bowel of mice do not proliferate, i.e. are tolerant when exposed to bacterial sonicates derived from autologous intestine (BsA) but do proliferate, i.e. are immune when exposed to bacterial sonicates derived from the heterologous intestine of syngenic littermates (BsH). Furthermore, we demonstrate that both local and systemic tolerance to BsA is broken in a murine model of chronic intestinal inflammation induced by the hapten reagent 2,4,6-trinitrobenzene sulfonic acid (TNBS), which mimics several important characteristics of Crohn's disease. Tolerance to BsA was restored and TNBS-induced colitis was abrogated in mice systemically treated with interleukin (IL)-10 or antibodies to IL-12. Treatment specifically restored tolerance to BsA, but did not suppress proliferation to BsH. In summary, we here report a new mouse model for the study of immunity and tolerance towards bacterial products. Our data suggest that tolerance to BsA is an important protective mechanism and that restoration of tolerance to resident intestinal flora by IL-10 and antibodies to IL-12 may be of potential therapeutic utility in patients with inflammatory bowel disease.     

大肠埃希氏菌在葡聚糖硫酸钠诱导的结肠炎恢复中的作用

目的: 随着对炎症性肠病(inflammatory bowel disease,IBD) 发病机制的深入研究, 肠道正常菌群与肠道炎症的密切关系日益受到重视。本研究旨在评价肠道大肠埃希氏菌( E.coli )对葡聚糖硫酸钠(dextran sulfate sodium,DSS) 诱导的小鼠结肠炎肠道黏膜的保护作用及其可能机制。方法: BALB/c 小鼠饮用含 3.5%DSS的饮用水 5 d, 诱导小鼠急性结肠炎, 模拟人类溃疡性结肠炎。 空白对照组饮用未添加 DSS的饮用水。饮用DSS的小鼠随机分为 3组, 分别给予不同的处理: (1) 单纯DSS 处理组; (2) 细菌耗竭小鼠(bacteria-depleted mice,BD小鼠)单纯DSS处理组; (3) 细菌耗竭小鼠大肠埃希氏菌处理组。从 4方面评价各组的处理反应: (1) 一般情况: 包括体重、疾病活动度(disease activity index, DAI)评分、结肠长度和重量; (2) 组织病理评分;(3) 化学比色法检测病变组织髓过氧化物酶(myeloperoxidase,MPO) 活性; (4) 免疫组织化学方法检测活化的核转录因子-κΒ(nuclear factor kappa B,NF-κB)。结果: 无E.coli处理的细菌耗竭小鼠难以从DSS诱导的肠炎中恢复。E.coli处理组和无E.coli处理组比较,大体评分、 组织病理评分和MPO活性明显改善(P<0.05)。E.coli处理组NF-κB活性显著高于无E.coli处理组 (均P<0.05)。结论: 肠道正常菌群是肠道炎症恢复的必需条件。大肠埃希氏菌能够促进小鼠DSS结肠炎的恢复;该作用与促进NF-κB的活化有关。     

Lactobacillus sakei K17, an inducer of IL-10 expression in antigen-presenting cells,attenuates TNBS-induced colitis in mice

To understand the anti-colitic effects of probiotics that up-regulate interleukin (IL)-10 expression in dendritic cells (DCs) and macrophages, we isolated Lactobacillus sakei K17, which potently induced IL-10 expression in DCs and peritoneal macrophages in vitro, among the lactic acid bacteria strains collected from kimchi and investigated its anti-inflammatory effect in mice with 2,4,6-trinitrobenzene sulfonic acid (TNBS)-induced colitis. Oral administration of K17 (2?×?10⁹ CFU·mouse^?1·day^?1) in mice with TNBS-induced colitis suppressed colon shortening and myeloperoxidase activity, as well as infiltration of CD86^+?cells into the colon. Treatment with K17 also increased TNBS-suppressed expression of tight junction proteins and IL-10, but inhibited activation of nuclear factor-kappaB (NF-κB) and mitogen-activated protein kinases and expression of tumor necrosis factor α and IL-17. Its effect was comparable with that of sulfasalazine (50?mg/kg), a positive commercial ant-colitic drug. Furthermore, treatment with K17 (1?×?10⁵ CFU/mL) potently inhibited lipopolysaccharide (LPS)-stimulated NF-κB activation in DCs and peritoneal macrophages and restored tight junction protein expression in LPS-stimulated Caco-2 cells. These findings suggest that Lactobacillus sakei K17 may ameliorate colitis by up-regulating the expression of IL-10 and tight junction proteins and inhibiting NF-κB activation.     

Effect of Trichinella spiralis infection on passive cutaneous anaphylaxis in mice.

Infection of CFW mice with Trichinella spiralis induced a state of relative unresponsiveness to passive cutaneous anaphylaxis (PCA) induced with hen egg albumin and its corresponding antibodies. The unresponsiveness was to PCA produced either with immunoglobulin G1 (IgG1) or IgE type of antibodies, but was more pronounced with the latter. As few as 25 larvae given by stomach tube 20 days before induced this resistance, although 400 larvae induced a greater resistance. When 400 to 600 larvae were fed to mice, the refractoriness of these mice to PCA was noticed 15 days later. The sera of infected mice had the ability to inhibit mainly PCA induced by IgE. This inhibitory property of sera from infected mice was more pronounced 35 days after infection than 10 months later, when only weak inhibitory activity was detected. Purified rat IgE inhibited the PCA reactions induced in both mice and rats with mouse IgE-type antibody. At high concentrations, evidence of inhibition of the IgG1-induced PCA in mice was also obtained. We believe that the relative unresponsiveness of infected mice is due to an increase in production of IgE which competitively blocks the mast cell sites for other IgE molecules.     

Inhibition of NKG2D receptor function by antibody therapy attenuates transfer-induced colitis in SCID mice

A role for the activating NK-receptor NKG2D has been indicated in several autoimmune diseases in humans and in animal models of type 1 diabetes and multiple sclerosis, and treatment with monoclonal antibodies to NKG2D attenuated disease severity in these models. In an adoptive transfer-induced model of colitis, we found a significantly higher frequency of CD4(+)NKG2D(+) cells in blood, mesenteric lymph nodes, colon, and spleen from colitic mice compared to BALB/c donor-mice. We, therefore, wanted to study the effect of anti-NKG2D antibody (CX5) treatment initiated either before onset of colitis, when the colitis was mild, or when severe colitis was established. CX5 treatment decreased the detectable levels of cell-surface NKG2D and prophylactic administration of CX5 attenuated the development of colitis significantly, whereas a more moderate reduction in the severity of disease was observed after CX5 administration to mildly colitic animals. CX5 did not attenuate severe colitis. We conclude that the frequency of CD4(+)NKG2D(+) cells increase during development of experimental colitis. NKG2D may play a role in the early stages of colitis in this model, since early administration of CX5 attenuated disease severity.     

Galectin-2 induces apoptosis of lamina propria T lymphocytes and ameliorates acute and chronic experimental colitis in mice

Galectins have recently emerged as central regulators of the immune system. We have previously demonstrated that carbohydrate-dependent binding of galectin-2 induces apoptosis in activated T cells. Here, we investigate the potential therapeutic effect of galectin-2 in experimental colitis. Galectin-2 expression and its binding profile were determined by immunohistochemistry. Acute and chronic colitis was induced by dextran sodium sulfate administration and in a T-cell transfer colitis model. Apoptosis was assessed by TdT-mediated dUTP-biotin nick-end labeling, and cytokine secretion was determined by cytometric bead array. We show that galectin-2 was constitutively expressed mainly in the epithelial compartment of the mouse intestine and bind to lamina propria mononuclear cells. During colitis, galectin-2 expression was reduced, but could be restored to normal levels by immunosuppressive treatment. Galectin-2 treatment induced apoptosis of mucosal T cells and thus ameliorated acute and chronic dextran-sodium-sulfate-induced colitis and in a T-helper-cell 1-driven model of antigen-specific transfer colitis. Furthermore, the pro-inflammatory cytokine release was inhibited by galectin-2 treatment. In preliminary toxicity studies, galectin-2 was well tolerated. Our study provides evidence that galectin-2 induces apoptosis in vivo and ameliorates acute and chronic murine colitis. Furthermore, galectin-2 has no significant toxicity over a broad dose range, suggesting that it may serve as a new therapeutic agent in the treatment of inflammatory bowel disease.

Leptin antagonist ameliorates chronic colitis in IL-10 mice

Background

Although the etiology of two major forms of inflammatory bowel disease (IBD), Crohn's disease (CD) and ulcerative colitis (UC) are unknown and evidence suggests that chronic intestinal inflammation is caused by an excessive immune response to mucosal antigens. Previous studies support the role for TGF-β1 through 3 in the initiation and maintenance of tolerance via the induction of regulatory T cells (Tregs) to control intestinal inflammation. Leptin, a satiety hormone produced primarily by adipose tissue, has been shown to increase during colitis progression and is believed to contribute to disease genesis and/or progression.

Aim

We investigated the ability of a pegylated leptin antagonist (PG-MLA) to ameliorate the development of chronic experimental colitis.

Results

Compared to vehicle control animals, PG-MLA treatment of mice resulted in an (1) attenuated clinical score; (2) reversed colitis-associated pathogenesis including a decrease in body weight; (3) reduced systemic and mucosal inflammatory cytokine expression; (4) increased insulin levels and (5) enhanced systemic and mucosal Tregs and CD39⁺ Tregs in mice with chronic colitis. The percentage of systemic and mucosal TGF-β1, -β2 and -β3 expressing CD4⁺ T cells were augmented after PG-MLA treatment. The activation of STAT1 and STAT3 and the expression of Smad7 were also reduced after PG-MLA treatment in the colitic mice. These findings clearly suggest that PG-MLA treatment reduces intestinal Smad7 expression, restores TGF-β1-3 signaling and reduces STAT1/STAT3 activation that may increase the number of Tregs to ameliorate chronic colitis.

Conclusion

This study clearly links inflammation with the metabolic hormone leptin suggesting that nutritional status influences immune tolerance through the induction of functional Tregs. Inhibiting leptin activity through PG-MLA might provide a new and novel therapeutic strategy for the treatment of IBD.     

Role of histamine in a rat model of colitis

We examined the possible involvement of mast cells in a rat model of colitis, by monitoring levels of histamine at various times after inducing inflammation with intrarectal trinitrobenzene sulfonic acid in 50% ethanol. The ability of a histamine H₁ antagonist, diphenhydramine, to modify colitis was also assessed. As expected, trinitrobenzene sulfonic acid in 50% ethanol induced a sustained colitis. Myeloperoxidase levels in macroscopically damaged tissue peaked at one week, and declined thereafter. In contrast, tissue histamine levels were normal at one week, then increased in damaged tissue to approximately four times normal levels at four weeks. Indices of inflammation were markedly suppressed at one week by diphenhydramine, while tissue histamine levels were unaffected. Chronic colitis in rats is thus apparently accompanied by a local mast cell hyperplasia or influx. Moreover, antagonism of a major mast cell mediator, histamine, significantly reduces the severity of inflammation in this model.Abbreviations MPO myeloperoxidas - SCF stem cell factor - TNB trinitrobenzene sulfonic acid     

Neither direct nor developmental exposure to bisphenol A alters the severity of experimental inflammatory colitis in mice

Abstract

Bisphenol A (BPA) is a high production volume endocrine disrupting chemical that is widely used in many consumer products and prevalent in human biological fluids. Recent studies suggest that BPA is active even at low levels, raising concern about its potential harm to human health. Given that the main route of exposure to BPA is oral, via the consumption of BPA-tainted foods and beverages, intestinal tissues could be particularly vulnerable to BPA-induced changes. A novel examination is reported here of whether oral exposure to BPA affects inflammatory bowel disease (IBD), an immune-mediated disease of the colon, using a mouse model of inflammatory colitis. In addition to direct exposure, the possible contribution of maternal BPA exposure to disease later in life is explored. It was found that daily oral exposure to BPA at the US Environmental Protection Agency described oral reference dose (50?µg/kg/day), either via direct oral route or through maternal sources (i.e. developmental exposure), did not significantly alter disease outcomes of body weight, survival, or colonic pathology. These observations suggest that oral BPA exposure, at this dose and for this exposure duration, has minimal influence on aspects of the inflammatory response that regulate immune mediated diseases of the gastrointestinal tract.     

Effect of methylprednisolone on the ulceration, matrix metalloproteinase distribution and eicosanoid production in a model of colitis in the rabbit

This study has examined the response of a rabbit model of inflammatory bowel disease to methylprednisolone. Colitis was induced in the colon of rabbits with 40 mg trinitrobenzenesulphonic acid in 25% ethanol (TNBS). The effect of methylprednisolone (0.5 mg/kg/day) on the development of colitis was determined at one week, by examining the colon's macroscopic and microscopic appearance, the distribution of matrix metalloproteinases (MMPs) and by measuring eicosanoid production. Although there was no difference in the area of ulcerated colonic tissue in the treated and untreated TNBS animals, the increase in polymorphonuclear leucocytes was significantly reduced in TNBS rabbits given methylprednisolone. The only difference in the distribution of MMPs was a reduction in the number of polymorphonuclear leucocytes containing gelatinase B. The release of immunoreactive PGE₂ and LTB₄, but not 6-keto PG F _1α, was increased in the TNBS animals and was unchanged by methylprednisolone. These results show that methylprednisolone does not modify the injury produced by TNBS in this model despite reducing the infiltration of polymorphonuclear leucocytes. Hence it suggests that these cells do not contribute to the injury observed, are not the source of the eicosanoids and that gelatinase B is not required in the healing process in this model.     

IL-28B对小鼠结肠炎的抑制作用及其机制研究

目的:研究IL-28B对葡聚糖硫酸钠(dextran sodium sulfate,DSS)诱导的小鼠结肠炎的作用和机制。方法:35只雄性C57BL/6小鼠随机分为对照组、DSS组以及IL-28B治疗组(1.25 μg、2.5 μg和5 μg),每组7只。DSS组与IL-28B治疗组饮用2.5% DSS。从第3天开始,...     

Anemia and retinal function in a mouse model of acute colitis

Individuals with inflammatory bowel diseases (IBD) have an elevated risk of ocular inflammation. Both the anterior and posterior eye can be affected by IBD, although posterior eye dysfunction is more likely to go undetected. Little investigative attention has been directed toward the mechanisms of ocular dysfunction with IBD; however, given the prevalence of anemia in IBD and the effects of anemia on the retina, we examined the association between retinal function (electroretinography, ERG) and the anemia induced by experimental IBD, and we tested for a potential retinal benefit of acutely attenuating anemia (via red blood cell (RBC) infusion). Colitis was induced in mice in a model involving drinking water ingestion of dextran sodium sulfate (DSS), with untreated drinking water administered to controls. A subset of the DSS mice was infused with RBCs to attenuate the severity of the anemia induced by DSS. ERG signals (a-waves, b-waves, and oscillatory potential amplitudes and implicit times) were compared between the three groups of mice to evaluate retinal function. ERG amplitudes were significantly decreased in DSS mice compared to controls, with the amplitudes demonstrating a positive correlation with hematocrit, that is, the lowest ERG amplitudes were found with the most severe cases of anemia. An acute infusion of RBCs into DSS mice provided an improvement in the oscillatory potential implicit times, but no significant improvements in other ERG parameters. Despite the association between anemia and ERG signals in DSS-induced colitis, acute RBC infusion may only partially attenuate the associated retinal dysfunction.     

Persistence of Trichinella spiralis muscle larvae in natural decaying mice

The influence of natural weather conditions on the viability and reproductive capability of Trichinella spiralis muscle larvae in mouse corpses exposed to summer and winter conditions in the Buenos Aires Province, Argentina, was studied. For this purpose, a total of 49 mouse corpses harbouring muscle larvae of T. spiralis were exposed for a period of 1, 2, 4 and 6 weeks in each of the seasons. Control corpses maintained at 8°C were also included. In summer, T. spiralis muscle larvae were recovered from corpses exposed up to 1 week only. The viability of these larvae was 54.2%, and the reproductive capability index in mice (RCI) was 13.1 and significantly lower than the control (p<0.0005). Morphologic deterioration and reduction in the glycogen content of cysts and larvae were observed at the second week of exposition. By week 4, larval stages of Dermestes maculatus were observed inside corpses, and 22 live muscle larvae of T. spiralis were obtained by artificial digestion of their bodies. In winter, T. spiralis muscle larvae were always recovered, the viability being almost 100% except for a significant reduction by week 6 of exposition (p<0.0001). For this season, the RCI were 50.5, 46.9, 59.7 and 45.2 for the periods of 1, 2, 4 and 6 weeks of exposition, respectively. The morphology of cysts and larvae did not show alterations, and no variations were observed as well in glycogen reserves during the 6-week period of exposition. RCI of non-exposed muscle larvae were always significantly higher that any of those recorded from muscle larvae that belonged to exposed corpses (p=0.0005). The present results demonstrate that muscle larvae of T. spiralis are able to survive in nature and keep infective for a 1-week period in summer and at least for 6 weeks in winter, becoming an important source of infection for scavengers. In summer, larvae stages of D. maculatus, and probably other insects, may play an important role in the survival and transmission of T. spiralis in the sylvatic cycle.