Induction of thymocyte apoptosis by systemic administration of concanavalin A in mice: role of TNF-alpha, IFN-gamma and glucocorticoids

CD8 T cell tolerance results from eviction of immature autoreactive cells from the thymus

CD8 T cell tolerance is thought to result from clonal deletion of autoreactive thymocytes before they differentiate into mature CD8 T cells in the thymus. However, we report that, in mice, CD8 T cell tolerance instead results from premature thymic eviction of immature autoreactive CD8 thymocytes into the periphery, where they differentiate into self-tolerant mature CD8 T cells. Premature thymic eviction is triggered by T cell receptor (TCR)-driven down-regulation of the transcriptional repressor Gfi1, which induces expression of sphingosine-1-phosphate receptor-1 (S1P1) on negatively selected immature CD8 thymocytes. Thus, premature thymic eviction is the basis for CD8 T cell tolerance and is the mechanism responsible for the appearance in the periphery of mature CD8 T cells bearing autoreactive TCRs that are absent from the thymus.

IFNγ and iNOS-Mediated Alterations in the Bone Marrow and Thymus and Its Impact on Mycobacterium avium-Induced Thymic Atrophy

Disseminated infection with the high virulence strain of Mycobacterium avium 25291 leads to progressive thymic atrophy. We previously showed that M. avium-induced thymic atrophy results from increased glucocorticoid levels that synergize with nitric oxide (NO) produced by interferon gamma (IFNγ) activated macrophages. Where and how these mediators act is not understood. We hypothesized that IFNγ and NO promote thymic atrophy through their effects on bone marrow (BM) T cell precursors and T cell differentiation in the thymus. We show that M. avium infection cause a reduction in the percentage and number of common lymphoid progenitors (CLP). Additionally, BM precursors from infected mice show an overall impaired ability to reconstitute thymi of RAGKO mice, in part due to IFNγ. Thymi from infected mice present an IFNγ and NO-driven inflammation. When transplanted under the kidney capsule of uninfected mice, thymi from infected mice are unable to sustain T cell differentiation. Finally, we observed increased thymocyte death via apoptosis after infection, independent of both IFNγ and iNOS; and a decrease on active caspase-3 positive thymocytes, which is not observed in the absence of iNOS expression. Together our data suggests that M. avium-induced thymic atrophy results from a combination of defects mediated by IFNγ and NO, including alterations in the BM T cell precursors, the thymic structure and the thymocyte differentiation.

The Potential Protective Effect of Iridoid Glycosides Isolated From Osmanthus fragrans Seeds Against the Development of Immune Liver Injury in Mice

Objective: The iridoid glycosides were extracted and separated from Osmanthus fragrans seeds, and the potential protective effect of Osmanthus fragrans seed extract on concanavalin A-induced immune liver injury in mice was studied.

Methods:Osmanthus fragrans seeds were extracted by 95% ethanol reflux. Then, the iridoid glycosides were enriched by extraction refined through petroleum ether (60°C–90°C), ethyl acetate, and water-saturated n-butanol in sequence, so as to purify the n-butanol part (Osmanthus fragrans seed’s n-butanol extraction, OFSN) by macroporous resin. Specnuezhenide and Nuezhenoside G13 were used as the reference substances to determine the concentration of iridoid glycosides by HPLC. On this basis, a mouse immune liver injury model was established by tail intravenous concanavalin A (20 mg/kg); the contents of serum ALT, AST, IFN-γ, and TNF-α and the contents of liver tissue MDA and SOD were determined; the pathological changes of the liver by HE staining were observed; and the expression levels of p38MAPK and p-p38mapk in liver tissue were detected by WB.

Results: The linearity, precision, repeatability, recovery, and stability of HPLC all met the requirements by validating with the methodology. The contents of Specnuezhenide and Nuezhenoside G13 in the n-butanol extracts were 39.20% and 39.88%, respectively. Actually, their contents can reach up to 82.56% and 87.9% after being purified by macroporous resin. The results of animal experiments show that OFSN could significantly reduce the liver and spleen index, reduce the ALT and AST contents in plasma and the MDA content in liver tissue, and then increase the SOD content. Besides, OFSN could also reduce the plasma IFN-γ and TNF-α levels. The HE staining result indicates that the pathological changes in the liver tissues of mice treated with OFSN are alleviated to different degrees while the WB result suggests that OFSN could significantly inhibit the expression of p-p38mapk.

Conclusion:Osmanthus fragrans seeds are rich in iridoid glycosides, which has a good protective effect on mouse immune liver injury caused by concanavalin A. The mechanism may be related to inhibiting the phosphorylation of p38MAPK, inhibiting the release of inflammatory mediators, improving the antioxidant capacity of liver cells, and weakening the occurrence of lipid peroxidation.

Roles of hepatic stellate cells in acute liver failure: From the perspective of inflammation and fibrosis

Acute liver failure (ALF) usually results in hepatocellular dysfunction and coagulopathy and carries a high mortality rate. Hepatic stellate cells (HSCs) are famous for their role in liver fibrosis. Although some recent studies revealed that HSCs might participate in the pathogenesis of ALF, the accurate mechanism is still not fully understood. This review focuses on the recent advances in understanding the functions of HSCs in ALF and revealed both protective and promotive roles during the pathogenesis of ALF: HSC activation participates in the maintenance of cell attachment and the architecture of liver tissue via extracellular matrix production and assists liver regeneration by producing growth factors; and HSC inflammation plays a role in relaying inflammation signaling from sinusoids to parenchyma via secretion of inflammatory cytokines. A better understanding of roles of HSCs in the pathogenesis of ALF may lead to improvements and novel strategies for treating ALF patients.

The Protective Effect of Sheep Placental Extract on Concanavalin A-induced Liver Injury in Mice

Though the biological effects of human placental extract have been widely studied, it has limited availability and its use poses ethical problems. Thus, domestic animal placental extracts are suggested as alternatives. In this study, the protective effect of sheep placental extract (SPE) on concanavalin A (Con A)-induced liver injury was investigated. BALB/c mice were randomly divided into six groups, including one normal group and five experimental groups, which received different oral doses of SPE (0, 5, 10 and 50 mg/kg) or a mixture of amino acids for 3 days before Con A injection. Compared with Con A-induced model group, the SPE administration significantly decreased serum aminotransaminase activity, alleviated pathological changes, recovered liver antioxidant capacity and prevented the increase of nitric oxide. Secretion of pro-inflammatory cytokines in serum decreased and mRNA expression of hepatic intercellular adhesion molecule-1, interferon-inducible chemokine 10 and inducible nitric oxide synthase were downregulated, while B-cell lymphoma-2 expression increased. The administration of amino acids mixture had no significant effect in most measurements compared with the model group, which indicated proteins and peptides, rather than individual amino acid, were largely responsible for the bioactivity of SPE. The results indicate SPE has potential therapeutic effects against immune-mediated hepatitis.

Elevated intrathymic sphingosine-1-phosphate promotes thymus involution during sepsis

Sepsis mouse models revealed thymus atrophy, characterised by decreased thymus weight and loss of thymocytes due to apoptosis. Mice suffered from lymphopenia, a lack of T cells in the periphery, which attenuates their ability to fight against recurring and secondary infections during sepsis progression. Key players in thymus atrophy are IL-6, which is directly involved in thymus involution, and the sphingosine-1-phosphate - sphingosine-1-phosphate receptor 1 signaling, influencing thymocytes emigration. In healthy individuals a sphingosine-1-phosphate (S1P) gradient from lymphoid organs to the circulatory system serves as signal for mature T cell egress. In the present study we investigated, whether inhibition of S1P generation improves thymus involution. In sepsis, induced by cecal ligation and puncture (CLP), S1P in the thymus increased, while it decreased in serum, thus disrupting the naturally occurring S1P gradient. As a potential source of S1P we identified increased numbers of apoptotic cells in the thymic cortex of septic mice. Pharmacological inhibition of the S1P generating sphingosine kinases, by 4- [[4-(4-Chlorophenyl)-2-thiazolyl]amino]phenol (SK I-II), administered directly following CLP, prevented thymus atrophy. This was reflected by lymphocytosis, diminished apoptosis, decreased IL-6 expression, and an unaltered thymus weight. In addition SK I-II-treatment preserved the S1P balance and prevented S1P-dependent internalization of the sphingosine-1-phosphate receptor 1. Our data suggest that inhibition of sphingosine kinase and thus, S1P generation during sepsis restores thymic T cell egress, which might improve septic outcome.

Differential susceptibility and maturation of thymocyte subsets during Salmonella Typhimurium infection: insights on the roles of glucocorticoids and Interferon-gamma

The thymus is known to atrophy during infections; however, a systematic study of changes in thymocyte subpopulations has not been performed. This aspect was investigated, using multi-color flow cytometry, during oral infection of mice with Salmonella Typhimurium (S. Typhimurium). The major highlights are: First, a block in the developmental pathway of CD4-CD8- double negative (DN) thymocytes is observed. Second, CD4+CD8+ double positive (DP) thymocytes, mainly in the DP1 (CD5loCD3lo) and DP2 (CD5hiCD3int), but not DP3 (CD5intCD3hi), subsets are reduced. Third, single positive (SP) thymocytes are more resistant to depletion but their maturation is delayed, leading to accumulation of CD24hiCD3hi SP. Kinetic studies during infection demonstrated differences in sensitivity of thymic subpopulations: Immature single positive (ISP) > DP1, DP2 > DN3, DN4 > DN2 > CD4+ > CD8+. Upon infection, glucocorticoids (GC), inflammatory cytokines, e.g. Ifnγ, etc are induced, which enhance thymocyte death. Treatment with RU486, the GC receptor antagonist, increases the survival of most thymic subsets during infection. Studies with Ifnγ-/- mice demonstrated that endogenous Ifnγ produced during infection enhances the depletion of DN2-DN4 subsets, promotes the accumulation of DP3 and delays the maturation of SP thymocytes. The implications of these observations on host cellular responses during infections are discussed.

NK-cells are involved in thymic atrophy induced by influenza A virus infection

NK-cells have traditionally been viewed as innate effector lymphocytes that serve as a first line of defence against a range of viruses and tumours. More recently, the importance of NK-cell immunoregulatory functions has been highlighted. NK-cells can inhibit antiviral T-cell responses, and also play an important role in controlling harmful T-cell activity in autoimmunity and transplantation settings. Moreover, immunopathological effects of NK-cells during infection have been reported. Nevertheless, the phenotype and function of NK-cells in the thymus during influenza virus infection is not understood. In the present study, we demonstrated that influenza A virus (IAV) infection in mice led to severe thymic atrophy caused by increased thymic T-cell apoptosis and suppressed proliferation. We found that NK-cells played a critical role in this phenotype. IFN-c production by NK-cells was a contributing factor for thymic atrophy during IAV infection. Taken together, our data indicate that NK-cells are involved in the thymic atrophy associated with IAV infection.

Lethal and nonlethal murine malarial infections differentially affect apoptosis, proliferation, and CD8 expression on thymic T cells

Although thymic atrophy and apoptosis of the double-positive (DP) T cells have been reported in murine malaria, comparative studies investigating the effect of lethal and nonlethal Plasmodium infections on the thymus are lacking. We assessed the effects of P. yoelii lethal (17XL) and nonlethal (17XNL) infections on thymic T cells. Both strains affected the thymus. 17XL infection induced DP T-cell apoptosis and a selective decrease in surface CD8 expression on developing thymocytes. By contrast, more severe but reversible effects were observed during 17XNL infection. DP T cells underwent apoptosis, and proliferation of both DN and DP cells was affected around peak parasitemia. A transient increase in surface CD8 expression on thymic T cells was also observed. Adult thymic organ culture revealed that soluble serum factors, but not IFN-γ or TNF-α, contributed to the observed effects. Thus, lethal and nonlethal malarial infections led to multiple disparate effects on thymus. These parasite-induced thymic changes are expected to impact the naïve T-cell repertoire and the subsequent control of the immune response against the parasite. Further investigations are required to elucidate the mechanism responsible for these disparate effects, especially the reversible involution of the thymus in case of nonlethal infection.

MORPHOLOGICAL CHANGES IN MICE LIVER IN DYNAMICS OF CONCANAVALIN A - INDUCED HEPATITIS

The injure of the liver tissue and its infiltration by cells of the innate and adaptive immunity in dynamics of Con A-induced hepatitis in mice was studied. The semiquantitative method of damage rate of microcirculation channel and liver parenchyma was used, leukocyte liver infiltration and cellular composition of infiltrates were investigated also. Primary liver reaction to the Con-A was the inflammatory changes in the vascular bed, followed by disturbances in the parenchyma.The sufficient increasing of leukocyte migration to the liver was revealed. Besides, the neutrophile infiltration was increased first with a maximum at 6 hours of the experiment (63,9 ±4,6%, p<0,001 to the control level) ,and then the lymphocyte infiltration was increased with creation of manycellular lymphocytemacrophage infiltrates (62% at 48 hours comparing to 6 hours of experiment) and sufficient quantity of plasma cells population (4,9%, p<0,05 comparing to 6 hours of experiment). The obtained data gives the base to suggest that the elevated infiltration of liver tissue by leukocytes, particularly by lymphocytes and monocytes, together with necrotic death increasing creats the conditions for effective intracellular interaction and immune response to autoantigenes. This can be the essential pathogenic mechanism of development of autoimmune liver deseases.

Severe influenza A(H1N1)pdm09 infection induces thymic atrophy through activating innate CD8(+)CD44(hi) T cells by upregulating IFN-γ

Thymic atrophy has been described as a consequence of infection by several pathogens including highly pathogenic avian influenza virus and is induced through diverse mechanisms. However, whether influenza A(H1N1)pdm09 infection induces thymic atrophy and the mechanisms underlying this process have not been completely elucidated. Our results show that severe infection of influenza A(H1N1)pdm09 led to progressive thymic atrophy and CD4⁺CD8⁺ double-positive (DP) T-cells depletion due to apoptosis. The viruses were present in thymus, where they activated thymic innate CD8⁺CD44^hi single-positive (SP) thymocytes to secrete a large amount of IFN-γ. Milder thymic atrophy was observed in innate CD8⁺ T-cell-deficient mice (C57BL/6J). Neutralization of IFN-γ could significantly rescue the atrophy, but peramivir treatment did not significantly alleviate thymic atrophy. In this study, we demonstrated that thymic innate CD8⁺CD44^hi SP T-cells have critical roles in influenza A(H1N1)pdm09 infection-induced thymic atrophy through secreting IFN-γ. This exceptional mechanism might serve as a target for the prevention and treatment of thymic atrophy induced by influenza A(H1N1)pdm09.

Interferon-γ- and glucocorticoid-mediated pathways synergize to enhance death of CD4(+) CD8(+) thymocytes during Salmonella enterica serovar Typhimurium infection

Thymic atrophy is known to occur during infections; however, there is limited understanding of its causes and of the cross-talk between different pathways. This study investigates mechanisms involved in thymic atrophy during a model of oral infection by Salmonella enterica serovar Typhimurium (S. typhimurium). Significant death of CD4(+) CD8(+) thymocytes, but not of single-positive thymocytes or peripheral lymphocytes, is observed at later stages during infection with live, but not heat-killed, bacteria. The death of CD4(+) CD8(+) thymocytes is Fas-independent as shown by infection studies with lpr mice. However, apoptosis occurs with lowering of mitochondrial potential and higher caspase-3 activity. The amounts of cortisol, a glucocorticoid, and interferon-γ (IFN-γ), an inflammatory cytokine, increase upon infection. To investigate the functional roles of these molecules, studies were performed using Ifnγ(-/-) mice together with RU486, a glucocorticoid receptor antagonist. Treatment of C57BL/6 mice with RU486 does not affect colony-forming units (CFU), amounts of IFN-γ and mouse survival; however, there is partial rescue in thymocyte death. Upon infection, Ifnγ(-/-) mice display higher CFU and lower survival but more surviving thymocytes are recovered. However, there is no difference in cortisol amounts in C57BL/6 and Ifnγ(-/-) mice. Importantly, the number of CD4(+) CD8(+) thymocytes is significantly higher in Ifnγ(-/-) mice treated with RU486 along with lower caspase-3 activity and mitochondrial damage. Hence, endogenous glucocorticoid and IFN-γ-mediated pathways are parallel but synergize in an additive manner to induce death of CD4(+) CD8(+) thymocytes during S. typhimurium infection. The implications of this study for host responses during infection are discussed.

Galectin-3 deficiency prevents concanavalin A-induced hepatitis in mice

We used concanavalin A (Con A)-induced liver injury to study the role of galectin-3 (Gal-3) in the induction of inflammatory pathology and hepatocellular damage. We tested susceptibility to Con A-induced hepatitis in galectin-3-deficient (Gal-3(-/-)) mice and analyzed the effects of pretreatment with a selective inhibitor of Gal-3 (TD139) in wild-type (WT) C57BL/6 mice, as evaluated by a liver enzyme test, quantitative histology, mononuclear cell (MNC) infiltration, cytokine production, intracellular staining of immune cells, and percentage of apoptotic MNCs in the liver. Gal-3(-/-) mice were less sensitive to Con A-induced hepatitis and had a significantly lower number of activated lymphoid and dendritic cells (DCs) in the liver. The level of tumor necrosis factor alpha (TNFα), interferon gamma (IFNγ), and interleukin (IL)-17 and -4 in the sera and the number of TNFα-, IFNγ-, and IL-17- and -4-producing cluster of differentiation (CD)4(+) cells as well as IL-12-producing CD11c(+) DCs were lower, whereas the number of IL-10-producing CD4(+) T cells and F4/80(+) macrophages were significantly higher in livers of Gal-3(-/-) mice. Significantly higher percentages of late apoptotic Annexin V(+) propidium-idodide(+) liver-infiltrating MNCs and splenocytes were observed in Gal-3(-/-) mice, compared to WT mice. Pretreatment of WT C57BL/6 mice with TD139 led to the attenuation of liver injury and milder infiltration of IFNγ- and IL-17- and -4-producing CD4(+) T cells, as well as an increase in the total number of IL-10-producing CD4(+) T cells and F4/80(+) CD206(+) alternatively activated macrophages and prevented the apoptosis of liver-infiltrating MNCs.

CONCLUSIONS

Gal-3 plays an important proinflammatory role in Con A-induced hepatitis by promoting the activation of T lymphocytes and natural killer T cells, maturation of DCs, secretion of proinflammatory cytokines, down-regulation of M2 macrophage polarization, and apoptosis of MNCs in the liver.

Strain-dependent differences in bone development, myeloid hyperplasia, morbidity and mortality in ptpn2-deficient mice

Single nucleotide polymorphisms in the gene encoding the protein tyrosine phosphatase TCPTP (encoded by PTPN2) have been linked with the development of autoimmunity. Here we have used Cre/LoxP recombination to generate Ptpn2(ex2-/ex2-) mice with a global deficiency in TCPTP on a C57BL/6 background and compared the phenotype of these mice to Ptpn2(-/-) mice (BALB/c-129SJ) generated previously by homologous recombination and backcrossed onto the BALB/c background. Ptpn2(ex2-/ex2-) mice exhibited growth retardation and a median survival of 32 days, as compared to 21 days for Ptpn2(-/-) (BALB/c) mice, but the overt signs of morbidity (hunched posture, piloerection, decreased mobility and diarrhoea) evident in Ptpn2(-/-) (BALB/c) mice were not detected in Ptpn2(ex2-/ex2-) mice. At 14 days of age, bone development was delayed in Ptpn2(-/-) (BALB/c) mice. This was associated with increased trabecular bone mass and decreased bone remodeling, a phenotype that was not evident in Ptpn2(ex2-/ex2-) mice. Ptpn2(ex2-/ex2-) mice had defects in erythropoiesis and B cell development as evident in Ptpn2(-/-) (BALB/c) mice, but not splenomegaly and did not exhibit an accumulation of myeloid cells in the spleen as seen in Ptpn2(-/-) (BALB/c) mice. Moreover, thymic atrophy, another feature of Ptpn2(-/-) (BALB/c) mice, was delayed in Ptpn2(ex2-/ex2-) mice and preceded by an increase in thymocyte positive selection and a concomitant increase in lymph node T cells. Backcrossing Ptpn2(-/-) (BALB/c) mice onto the C57BL/6 background largely recapitulated the phenotype of Ptpn2(ex2-/ex2-) mice. Taken together these results reaffirm TCPTP's important role in lymphocyte development and indicate that the effects on morbidity, mortality, bone development and the myeloid compartment are strain-dependent.

Immune mechanisms of Concanavalin A model of autoimmune hepatitis

As a chronic inflammatory disease of the liver, the pa-thogenic mechanisms of autoimmune hepatitis (AIH) have not yet been elucidated, with prognosis and diagnosis remaining unsatisfied. Currently the only viable treatments of AIH are immunosuppressant application and liver transplantation. It is considered that lack of good animal AIH models is the main reason for the shortage of a simple and efficient cure. The Concanavalin A (Con A) model is a typical and well established model for investigating T-cell and macrophage dependent liver injury in mice, which closely mimics the pathogenesis mechanisms and pathological changes of patients, and is regarded as the best experimental model for AIH research so far. In this paper we elucidated the pathogenic mechanisms of AIH and the evolution of relative animal models. We go on to further focus on Con A-induced liver injury from the point of immunological mechanisms and the change of cytokine levels. Finally, we manifested the clinical significance of the AIH animal models and the challenges they would meet during their future development.

Restoration of p53 functions protects cells from concanavalin A-induced apoptosis

A great majority of human cancers encounter disruption of the p53 network. Identification and characterization of molecular components important in both p53-dependent and p53-independent apoptosis might be useful in developing novel therapies. Previously, we reported that concanavalin A (Con A) induced p73-dependent apoptosis of cells lacking functional p53. In the present study, we investigated the mechanism and role of p53 in protection from apoptosis induced by Con A. Treatment with Con A resulted in apoptosis of p53-null ovarian cancer, SKOV3, or Li-Fraumeni syndrome, MDAH041 (041), cells. However, their isogenic pairs, SKP53 and TR9-7, expressing wild-type p53 were much less sensitive and were protected by G(1) arrest. Inhibition of p53 function rendered these cells sensitive to Con A. Con A-induced apoptosis was accompanied by upregulation of forkhead box O1a (FOXO1a) and Bcl-2-interacting mediator (Bim), which were strongly inhibited after p53 expression and rescued after p53 ablation. Moreover, ablation of Bim by short hairpin RNA protected cells from apoptosis. Taken together, our study suggests that Con A induces apoptosis of cells lacking p53 by activating FOXO1a-Bim signaling and that expression of p53 protects these cells by inducing G(1) arrest and by downregulating the expression of both FOXO1a and Bim, identifying a novel cross-talk between FOXO1a and p53 transcription factors.

Accelerated thymic atrophy as a result of elevated homeostatic expression of the genes encoded by the TNF/lymphotoxin cytokine locus

TNF, lymphotoxin (LT)-alpha, LT-beta and LIGHT are members of a larger superfamily of TNF-related cytokines that can cross-utilize several receptors. Although LIGHT has been implicated in thymic development and function, the role of TNF and LT remains incompletely defined. To address this, we created a model of modest homeostatic overexpression of TNF/LT cytokines using the genomic human TNF/LT locus as a low copy number Tg. Strikingly, expression of Tg TNF/LT gene products led to profound early thymic atrophy characterized by decreased numbers of thymocytes and cortical thymic epithelial cells, partial block of thymocyte proliferation at double negative (DN) 1 stage, increased apoptosis of DN2 thymocytes and severe decline of T-cell numbers in the periphery. Results of backcrossing to TNFR1-, LTbetaR- or TNF/LT-deficient backgrounds and of reciprocal bone marrow transfers implicated both LT-alpha/LT-beta to LTbetaR and TNF/LT-alpha to TNFR1 signaling in accelerated thymus degeneration. We hypothesize that chronic infections can promote thymic atrophy by upregulating LT and TNF production.

Hydrogen from intestinal bacteria is protective for Concanavalin A-induced hepatitis

It is well known that some intestinal bacteria, such as Escherichia coli, can produce a remarkable amount of molecular hydrogen (H(2)). Although the antioxidant effects of H(2) are well documented, the present study examined whether H(2) released from intestinally colonized bacteria could affect Concanavalin A (ConA)-induced mouse hepatitis. Systemic antibiotics significantly decreased the level of H(2) in both liver and intestines along with suppression of intestinal bacteria. As determined by the levels of AST, ALT, TNF-alpha and IFN-gamma in serum, suppression of intestinal bacterial flora by antibiotics increased the severity of ConA-induced hepatitis, while reconstitution of intestinal flora with H(2)-producing E. coli, but not H(2)-deficient mutant E. coli, down-regulated the ConA-induced liver inflammation. Furthermore, in vitro production of both TNF-alpha and IFN-gamma by ConA-stimulated spleen lymphocytes was significantly inhibited by the introduction of H(2). These results indicate that H(2) released from intestinal bacteria can suppress inflammation induced in liver by ConA.

Reversible blockade of thymic output: an inherent part of TLR ligand-mediated immune response

TLRs constitute a first set of sensors that detect viral nucleic acids including dsRNA which triggers TLR3. We report the early, direct, and detrimental effect of polyinosine-polycytidilic acid treatment on T cell development. Inhibition of thymopoiesis was targeted to several thymocyte subpopulations. First, both a blockade of the double negative (DN)1-DN2 transition and a severe down-regulation of DN3-DN4 thymocyte proliferation were observed. In addition, an important decrease in the absolute numbers of double-positive thymocytes, concomitant with an increase in frequencies of apoptotic cells in this population were shown. This inhibition of thymopoiesis resulted in a reduced thymic output, as evidenced by a drop of the absolute numbers of naive T cells and TCR excision circles levels. The decrease in thymic cellularity and defects in thymic development were severely reduced, but not completely abolished in IFN-alpha/betaR(-/-) mice, showing a direct contribution of type I IFNs, known to be massively up-regulated in viral infections, to the inhibition of T cell development. Strikingly, the TCR repertoire in treated mice was biased toward shorter CDR3 lengths as a result of a decreased expression of TdT and Rag2. However, thymic integrity remained intact since thymopoiesis was restored both quantitatively and qualitatively 14 days after the cessation of polyinosine-polycytidilic acid treatment. These results demonstrate a novel immunomodulatory role for virally encoded TLR ligands and RNA sensors; they further illustrate the diversity of mechanisms that viruses use to interfere with the development of a pathogen-specific immune responses.

Overexpression of lymphotoxin in T cells induces fulminant thymic involution

Activated lymphocytes and lymphoid-tissue inducer cells express lymphotoxins (LTs), which are essential for the organogenesis and maintenance of lymphoreticular microenvironments. Here we describe that T-cell-restricted overexpression of LT induces fulminant thymic involution. This phenotype was prevented by ablation of the LT receptors tumor necrosis factor receptor (TNFR) 1 or LT beta receptor (LTbetaR), representing two non-redundant pathways. Multiple lines of transgenic Ltalphabeta and Ltalpha mice show such a phenotype, which was not observed on overexpression of LTbeta alone. Reciprocal bone marrow transfers between LT-overexpressing and receptor-ablated mice show that involution was not due to a T cell-autonomous defect but was triggered by TNFR1 and LTbetaR signaling to radioresistant stromal cells. Thymic involution was partially prevented by the removal of one allele of LTbetaR but not of TNFR1, establishing a hierarchy in these signaling events. Infection with the lymphocytic choriomeningitis virus triggered a similar thymic pathology in wt, but not in Tnfr1(-/-) mice. These mice displayed elevated TNFalpha in both thymus and plasma, as well as increased LTs on both CD8(+) and CD4(-)CD8(-) thymocytes. These findings suggest that enhanced T cell-derived LT expression helps to control the physiological size of the thymic stroma and accelerates its involution via TNFR1/LTbetaR signaling in pathological conditions and possibly also in normal aging.

Endogenous interferon-gamma is required for efficient skeletal muscle regeneration

The inflammatory response is thought to play important roles in tissue healing. The hypothesis of this study was that the inflammatory cytokine interferon (IFN)-gamma is produced endogenously following skeletal muscle injury and promotes efficient healing. We show that IFN-gamma is expressed at both mRNA and protein levels in skeletal muscle following injury, and that the time course of IFN-gamma expression correlated with the accumulation of macrophages, T-cells, and natural killer cells, as well as myoblasts, in damaged muscle. Cells of each type were isolated from injured muscle, and IFN-gamma expression was detected in each cell type. We also demonstrate that administration of an IFN-gamma receptor blocking antibody to wild-type mice impaired induction of interferon response factor-1, reduced cell proliferation, and decreased formation of regenerating fibers. IFN-gamma null mice showed similarly impaired muscle healing associated with impaired macrophage function and development of fibrosis. In vitro studies demonstrated that IFN-gamma and its receptor are expressed in the C2C12 muscle cell line, and that the IFN-gamma receptor blocking antibody reduced proliferation and fusion of these muscle cells. In summary, our results indicate that IFN-gamma promotes muscle healing, in part, by stimulating formation of new muscle fibers.

A Novel Role for p73 in the Regulation of Akt-Foxo1a-Bim Signaling and Apoptosis Induced by the Plant Lectin, Concanavalin A

Virtually all human cancers encounter disruption of the "p53 network." From a therapeutic point of view, it is important to devise strategies that eliminate cancer cells, which are often defective in functional p53 and protect p53-expressing normal cells. By comparing the response of a pair of isogenic cell lines, we identify a plant-derived compound, Concanavalin A (Con A), which differentially kills p53-null cells. Further, we find that p53 family member, p73, plays a critical role that is unmasked in the absence of p53. Con A treatment leads to induction of p73 and several others that are important mediators of apoptosis and act downstream, such as p21, Bax, Foxo1a, and Bim. Inactivation of p73 reverses the expression of these proteins and apoptosis. Inhibition of Akt activation sensitizes otherwise resistant cells. These observations thus reveal a novel role for p73 in the regulation of Akt-Foxo1a-Bim signaling and apoptosis especially when p53 is absent.

Lymphocyte Loss and Immunosuppression Following Acetaminophen-Induced Hepatotoxicity in Mice as a Potential Mechanism of Tolerance

Current evidence suggests that drug-induced liver disease can be caused by an allergic response (drug-induced allergic hepatitis, DIAH) induced by hepatic drug-protein adducts. The relatively low incidence of these reactions has led us to hypothesize that tolerogenic mechanisms prevent DIAH from occurring in most people. Here, we present evidence for the existence of one of these regulatory pathways. Following a hepatotoxic dose of acetaminophen in C57Bl/6 mice, lymphocyte loss that appeared to be due at least in part to apoptosis was noted in the spleen, thymus, and draining lymph nodes of the liver. There was no observable lymphocyte loss in the absence of hepatotoxicity. Acetaminophen-induced liver injury (AILI) also led to a functional suppression of the immune system as determined by the inhibition of a delayed-type hypersensitivity response to dinitrochlorobenzene. Further studies with adrenalectomized mice suggested a role for corticosterone in the depletion of lymphocytes following APAP-induced liver injury. In conclusion, these findings suggest that lymphocyte loss and immunosuppression following AILI may prevent subsequent occurrences of allergic hepatitis and possibly other forms of APAP-induced allergies induced by hepatic drug-protein adducts. Similar regulatory pathways may inhibit other hepatotoxic drugs from causing allergic reactions.

T cell-mediated hepatic inflammation modulates adiponectin levels in mice: role of tumor necrosis factor alpha

Experimental T cell-mediated hepatitis induced by concanavalin A (ConA) results in the initiation of an inflammatory response and the production of cytokines. Adiponectin is an adipocytokine produced by adipose tissue that is involved in the reciprocal regulation of other cytokines, including tumor necrosis factor alpha (TNF-alpha). Concanavalin A administration to C57BL/6J mice reduced circulating levels of adiponectin, whereas leptin was markedly increased. Adiponectin messenger RNA expression in adipose tissue was also decreased; however, the expression of both the adiponectin receptors remained unchanged. Neutralization of TNF-alpha reduced ConA-induced liver damage, and this was associated with restored circulating levels of adiponectin. These findings indicate that inflammation-induced TNF-alpha is a critical mediator of adipose-tissue-derived adiponectin in vivo.