Transforming growth factor beta is protective in host resistance against Listeria monocytogenes infection in mice

TGF-β signaling in health, disease, and therapeutics

Transforming growth factor (TGF)-β is a multifunctional cytokine expressed by almost every tissue and cell type. The signal transduction of TGF-β can stimulate diverse cellular responses and is particularly critical to embryonic development, wound healing, tissue homeostasis, and immune homeostasis in health. The dysfunction of TGF-β can play key roles in many diseases, and numerous targeted therapies have been developed to rectify its pathogenic activity. In the past decades, a large number of studies on TGF-β signaling have been carried out, covering a broad spectrum of topics in health, disease, and therapeutics. Thus, a comprehensive overview of TGF-β signaling is required for a general picture of the studies in this field. In this review, we retrace the research history of TGF-β and introduce the molecular mechanisms regarding its biosynthesis, activation, and signal transduction. We also provide deep insights into the functions of TGF-β signaling in physiological conditions as well as in pathological processes. TGF-β-targeting therapies which have brought fresh hope to the treatment of relevant diseases are highlighted. Through the summary of previous knowledge and recent updates, this review aims to provide a systematic understanding of TGF-β signaling and to attract more attention and interest to this research area.

Roles of host SUMOylation in bacterial pathogenesis

Bacteria frequently interfere with the post-translational modifications of host cells to facilitate their survival and growth after invasion. SUMOylation, a reversible post-translational modification process, plays an important role in biological life activities. In addition to being critical to host cell metabolism and survival, SUMOylation also regulates gene expression and cell signal transmission. Moreover, SUMOylation in eukaryotic cells can be used by a variety of bacterial pathogens to advance bacterial invasion. In this minireview, we focused on the role and mechanism of host SUMOylation in the pathogenesis of six important clinical bacterial pathogens (Listeria monocytogenes, Shigella flexneri, Salmonella Typhimurium, Klebsiella pneumoniae, Staphylococcus aureus, and Escherichia coli). Taken together, this review provided new insights for understanding the unique pathogen-host interaction based on host SUMOylation and provided a novel perspective on the development of new strategies to combat bacterial infections in the future.

The multi-faceted roles of TGF-β in regulation of immunity to infection

Transforming Growth Factor-β is a potent regulator of the immune system, acting at every stage from thymic differentiation, population of the periphery, control of responsiveness, tissue repair and generation of memory. It is therefore a central player in the immune response to infectious pathogens, but its contribution is often clouded by multiple roles acting on different cells in time and space. Hence, context is all-important in understanding when TGF-β is beneficial or detrimental to the outcome of infection. In this review, a full range of infectious agents from viruses to helminth parasites are explored within this framework, drawing contrasts and general conclusions about the importance of TGF-β in these diseases.

Type I Natural Killer T Cells as Key Regulators of the Immune Response to Infectious Diseases

The immune system must work in an orchestrated way to achieve an optimal response upon detection of antigens. The cells comprising the immune response are traditionally divided into two major subsets, innate and adaptive, with particular characteristics for each type. Type I natural killer T (iNKT) cells are defined as innate-like T cells sharing features with both traditional adaptive and innate cells, such as the expression of an invariant T cell receptor (TCR) and several NK receptors. The invariant TCR in iNKT cells interacts with CD1d, a major histocompatibility complex class I (MHC-I)-like molecule. CD1d can bind and present antigens of lipid nature and induce the activation of iNKT cells, leading to the secretion of various cytokines, such as gamma interferon (IFN-γ) and interleukin 4 (IL-4). These cytokines will aid in the activation of other immune cells following stimulation of iNKT cells. Several molecules with the capacity to bind to CD1d have been discovered, including α-galactosylceramide. Likewise, several molecules have been synthesized that are capable of polarizing iNKT cells into different profiles, either pro- or anti-inflammatory. This versatility allows NKT cells to either aid or impair the clearance of pathogens or to even control or increase the symptoms associated with pathogenic infections. Such diverse contributions of NKT cells to infectious diseases are supported by several publications showing either a beneficial or detrimental role of these cells during diseases. In this article, we discuss current data relative to iNKT cells and their features, with an emphasis on their driving role in diseases produced by pathogenic agents in an organ-oriented fashion.

A physical/psychological and biological stress combine to enhance endoplasmic reticulum stress

The generation of an immune response against infectious and other foreign agents is substantially modified by allostatic load, which is increased with chemical, physical and/or psychological stressors. The physical/psychological stress from cold-restraint (CR) inhibits host defense against Listeria monocytogenes (LM), due to early effects of the catecholamine norepinephrine (NE) from sympathetic nerves on β1-adrenoceptors (β1AR) of immune cells. Although CR activates innate immunity within 2h, host defenses against bacterial growth are suppressed 2-3 days after infection (Cao and Lawrence 2002). CR enhances inducible nitric oxide synthase (iNOS) expression and NO production. The early innate activation leads to cellular reduction-oxidation (redox) changes of immune cells. Lymphocytes from CR-treated mice express fewer surface thiols. Splenic and hepatic immune cells also have fewer proteins with free thiols after CR and/or LM, and macrophages have less glutathione after the in vivo CR exposure or exposure to NE in vitro. The early induction of CR-induced oxidative stress elevates endoplasmic reticulum (ER) stress, which could interfere with keeping phagocytized LM within the phagosome or re-encapsuling LM by autophagy once they escape from the phagosome. ER stress-related proteins, such as glucose-regulated protein 78 (GRP78), have elevated expression with CR and LM. The results indicate that CR enhances the unfolded protein response (UPR), which interferes with host defenses against LM. Thus, it is postulated that increased stress, as exists with living conditions at low socioeconomic conditions, can lower host defenses against pathogens because of oxidative and ER stress processes.

[Host responses to bacterial infections]

Pathogenic bacteria and host defense system have been evolved by their offense and defense. In vivo research is crucial for elucidation of interactions between them. I have investigated their offence and defense by various standpoints using mouse models of Listeria monocytogenes and Staphylococcus aureus infections. Herein, the results of my research including the roles of endogenous cytokines in host defense, the attenuation of host defense mechanism in obesity and diabetes, the development of vaccines against S. aureus infection by staphylococcal enterotoxin (SE) family molecules, and the emesis-inducing mechanism of SEA are described.

Listeria monocytogenes impairs SUMOylation for efficient infection

During infection, pathogenic bacteria manipulate the host cell in various ways to allow their own replication, propagation and escape from host immune responses. Post-translational modifications are unique mechanisms that allow cells to rapidly, locally and specifically modify activity or interactions of key proteins. Some of these modifications, including phosphorylation and ubiquitylation, can be induced by pathogens. However, the effects of pathogenic bacteria on SUMOylation, an essential post-translational modification in eukaryotic cells, remain largely unknown. Here we show that infection with Listeria monocytogenes leads to a decrease in the levels of cellular SUMO-conjugated proteins. This event is triggered by the bacterial virulence factor listeriolysin O (LLO), which induces a proteasome-independent degradation of Ubc9, an essential enzyme of the SUMOylation machinery, and a proteasome-dependent degradation of some SUMOylated proteins. The effect of LLO on Ubc9 is dependent on the pore-forming capacity of the toxin and is shared by other bacterial pore-forming toxins like perfringolysin O (PFO) and pneumolysin (PLY). Ubc9 degradation was also observed in vivo in infected mice. Furthermore, we show that SUMO overexpression impairs bacterial infection. Together, our results reveal that Listeria, and probably other pathogens, dampen the host response by decreasing the SUMOylation level of proteins critical for infection.

Activation of human NK cells by the bacterial pathogen-associated molecular pattern muramyl dipeptide

Muramyl dipeptide (MDP) is a bacterial pathogen associated molecular pattern derived from both Gram-positive and -negative bacteria. It is a specific ligand for nuclear oligomerization domain 2, a pattern recognition receptor best characterized for its role in immunosurveillance in the gut. In this study, we demonstrate that human peripheral blood NK cells express nuclear oligomerization domain 2 and respond to MDP. NK cells naturally internalize MDP leading to direct cell activation, including signaling through NFkappaB: characterized by p50/p65 heterodimers at early stimulations times and sustained activation of p50 homodimers. Moreover, MDP synergizes with IFN-alpha and IL-12 to activate NK cells and stimulate IFN-gamma secretion, suggesting a role for accessory cells in induction of an optimal NK cell response. Although IL-12 costimulation leads to a greater IFN-gamma response by NK cells, higher levels of CD69 in response to MDP are induced in the presence of IFN-alpha, suggesting that different pathogen-induced cytokine profiles will affect downstream NK cell responses. In contrast, MDP alone or in combination with either IFN-alpha or IL-12 only poorly increases NK cell cytotoxicity. In summary, this report identifies MDP as a bacterial pathogen associated molecular pattern that activates human NK cells.

TGF-β regulates pathology but not tissue CD8+ T cell dysfunction during experimentalTrypanosoma cruzi infection

Infection with the protozoan parasite Trypanosoma cruzi leads to chronic infection, with parasite persistence primarily in muscle tissue. CD8(+) T cells isolated from muscle tissue of T. cruzi-infected mice display decreased production of IFN-gamma in response to T cell receptor engagement. The expression of TGF-beta at the site of CD8(+) T cell dysfunction and parasite persistence suggested that this immunoregulatory cytokine might play a role in these processes. Mice expressing a T cell-specific dominant negative TGF-beta receptor type II (DNRII) were therefore infected with T. cruzi. Infection of DNRII mice resulted in massive CD8(+) T cell proliferation, leading to increased numbers but decreased frequencies of antigen-specific CD8(+) T cells in the spleen compared to wild-type mice. However, TGF-beta unresponsiveness failed to restore effector functions of CD8(+) T cells isolated from muscle tissue. Histological examination of skeletal muscle from T. cruzi-infected DNRII mice revealed an extensive cellular infiltrate, and DNRII mice displayed higher susceptibility to infection. Overall, while TGF-beta does not appear to be responsible for CD8(+) T cell unresponsiveness in peripheral tissue in T. cruzi-infected mice, these data suggest a role for TGF-beta in control of immunopathology in response to T. cruzi infection.

Transforming growth factor-beta regulation of immune responses

Transforming growth factor-beta (TGF-beta) is a potent regulatory cytokine with diverse effects on hemopoietic cells. The pivotal function of TGF-beta in the immune system is to maintain tolerance via the regulation of lymphocyte proliferation, differentiation, and survival. In addition, TGF-beta controls the initiation and resolution of inflammatory responses through the regulation of chemotaxis, activation, and survival of lymphocytes, natural killer cells, dendritic cells, macrophages, mast cells, and granulocytes. The regulatory activity of TGF-beta is modulated by the cell differentiation state and by the presence of inflammatory cytokines and costimulatory molecules. Collectively, TGF-beta inhibits the development of immunopathology to self or nonharmful antigens without compromising immune responses to pathogens. This review highlights the findings that have advanced our understanding of TGF-beta in the immune system and in disease.

A Dual Role For TGF-β1 in the Control and Persistence of Fungal Pneumonia

TGF-beta1 (TGF) has been implicated in the pathogenesis of several chronic infections and is thought to promote microbial persistence by interfering with macrophage function. In rats with experimental pulmonary cryptococcosis, increased lung levels of TGF were present at 12 mo of infection. Within the lung, expression of TGF localized to epithelioid cells and foamy macrophages in areas of inflammation. Increased TGF expression was also observed in the lungs of experimentally infected mice and a patient with pulmonary cryptococcosis. TGF reduced Ab and serum-mediated phagocytosis of Cryptococcus neoformans by rat alveolar macrophages (AM) and peripheral blood monocytes, and this was associated with decreased chemokine production and oxidative burst. Interestingly, TGF-treated rat AM limited both intracellular and extracellular growth of C. neoformans. Control of C. neoformans growth by TGF-treated rat AM was due to increased secretion of lysozyme, a protein with potent antifungal activity. The effects of TGF on the course of infection were dependent on the timing of TGF administration relative to the time of infection. TGF treatment of chronically infected rats resulted in reduced lung fungal burden, while treatment early in the course of infection resulted in increased fungal burden. In summary, our studies suggest a dual role for TGF in persistent fungal pneumonia whereby it contributes to the local control of infection by enhancing macrophage antifungal efficacy through increased lysozyme secretion, while limiting inflammation by inhibiting macrophage/monocyte phagocytosis and reducing associated chemokine production and oxidative burst.

TGF-beta: the perpetrator of immune suppression by regulatory T cells and suicidal T cells

Innate and adaptive immunity function to eliminate foreign invaders and respond to injury while enabling coexistence with commensal microbes and tolerance against self and innocuous agents. Although most often effective in accomplishing these objectives, immunologic processes are not fail-safe and may underserve or be excessive in protecting the host. Checks and balances to maintain control of the immune system are in place and are becoming increasingly appreciated as targets for manipulating immunopathologic responses. One of the most recognized mediators of immune regulation is the cytokine transforming growth factor-beta (TGF-beta), a product of immune and nonimmune cells. Emerging data have unveiled a pivotal role for TGF-beta as a perpetrator of suppression by CD4(+)CD25(+) regulatory T (Treg) cells and in apoptotic sequelae. Through its immunosuppressive prowess, TGF-beta effectively orchestrates resolution of inflammation and control of autoaggressive immune reactions by managing T cell anergy, defining unique populations of Treg cells, regulating T cell death, and influencing the host response to infections.

Suppression of host resistance to Listeria monocytogenes by acute cold/restraint stress: lack of direct IL-6 involvement

We conducted kinetic studies to evaluate the effects of acute cold/restraint stress (ACRS) on both primary and secondary host resistance to Listeria monocytogenes (LM). The involvement of IL-6 also was investigated using IL-6 knockout (KO) mice on the BALB/c background. ACRS dramatically increased the serum corticosterone levels, indicating that ACRS activated the hypothalamic-pituitary-adrenal (HPA) axis. ACRS significantly inhibited host resistance to LM during a primary but not a secondary LM infection. During the primary infection, ACRS caused a significant delay in clearance of LM, loss of body weight, reduced food/water intake, and elevated levels of pro-inflammatory cytokines (IL-6, IL-1beta, and TNFalpha) and IFNgamma. ACRS IL-6 KO mice showed higher LM burdens than did IL-6 KO controls, suggesting that IL-6 is not required for the ACRS-impairment of host resistance. Elevated levels of IL-1beta and TNFalpha may compensate for the absence of IL-6 and maintain the ACRS-induced impairment, in that the serum and splenic IL-1beta and TNFalpha levels were significantly higher in infected ACRS IL-6 KO mice, but not in control IL-6 KO mice, as compared to respective wild type controls. ACRS appears to inhibit IL-6 independent mechanisms associated with innate immunity and/or the development of adaptive immunity, but these reactions are unable to modulate the more efficient secondary immune responses.

Identification of tgh-2, a filarial nematode homolog of Caenorhabditis elegans daf-7 and human transforming growth factor beta, expressed in microfilarial and adult stages of Brugia malayi

A novel member of the transforming growth factor beta (TGF-beta) family has been identified in the filarial nematode parasite Brugia malayi by searching the recently developed Expressed Sequence Tag (EST) database produced by the Filarial Genome Project. Designated tgh-2, this new gene shows most similarity to a key product regulating dauer larva formation in Caenorhabditis elegans (DAF-7) and to the human down-modulatory cytokine TGF-beta. Homology to DAF-7 extends throughout the length of the 349-amino-acid (aa) protein, which is divided into an N-terminal 237 aa, including a putative signal sequence, a 4-aa basic cleavage site, and a 108-aa C-terminal active domain. Similarity to human TGF-beta is restricted to the C-terminal domain, over which there is a 32% identity between TGH-2 and TGF-beta1, including every cysteine residue. Expression of tgh-2 mRNA has been measured over the filarial life cycle. It is maximal in the microfilarial stage, with lower levels of activity around the time of molting within the mammal, but continues to be expressed by mature adult male and female parasites. Expression in both the microfilaria, which is in a state of arrested development, and the adult, which is terminally differentiated, indicates that tgh-2 may play a role other than purely developmental. This is consistent with our observation that TGH-2 is secreted by adult worms in vitro. Recombinant TGH-2 expressed in baculovirus shows a low level of binding to TGF-beta-receptor bearing mink lung epithelial cells (MELCs), which is partially inhibited (16 to 39%) with human TGF-beta, and activates plasminogen activator inhibitor-1 transcription in MELCs, a marker for TGF-beta-mediated transduction. Further tests will be required to establish whether the major role of B. malayi TGH-2 (Bm-TGH-2) is to modulate the host immune response via the TGF-beta pathway.

Molecular isolation and characterisation of carp transforming growth factor beta 1 from activated leucocytes

The transforming growth factor (TGF beta) family of proteins are a set of pleiotropic secreted signalling molecules with unique and potent immunoregulatory properties. In this study the molecular cloning of carp TGF beta 1 is reported. A partial cDNA of the TGF beta protein was initially identified from a cDNA pool, obtained by subtracting the cDNAs from Con A-induced carp head kidney leucocytes from uninduced carp head kidney leucocyte cDNA. The entire coding sequence was assembled by sequencing both ends of the cDNA clone by using an anchored PCR reaction. Sequence analysis revealed an ORF encoding a protein of 376 amino acids, containing the similar unique pattern of conserved cysteines (seven out of nine) in the cysteine knot structure which exists in all known TGF beta proteins. Compared with other animal TGF beta s, the cDNA clone shows approximately 59-42, 40-38 and 37-36% amino acid identity with TGF beta 1, TGF beta 3 and TGF beta 2 respectively. Carp TGF beta 1 is expressed at low levels in carp head kidney, spleen, egg and liver, whereas its messenger RNA level is increased after activation of the head kidney leucocytes with Con A. Sequence analysis and pattern of expression suggests that this is the carp TGF beta 1.

Cutting Edge: Anti-CD1 Monoclonal Antibody Treatment Reverses the Production Patterns of TGF-β2 and Th1 Cytokines and Ameliorates Listeriosis in Mice

Protection against intracellular bacteria by T cells is regulated by Ag-presenting molecules, which comprise classical MHC class I molecules, MHC class II molecules, and nonclassical MHC class Ib molecules. The role of CD1 molecules, which are structurally similar to classical MHC class I gene products, but less polymorphic, is not understood so far. We show that CD1 surface expression increased on APC in Listeria-infected mice. The in vivo treatment with anti-CD1 mAb reduced TGF-β2 levels and concomitantly increased secretion of the proinflammatory cytokine TNF, the Th1 cell promoting cytokine IL-12, and the Th1 cell cytokine IFN-γ at the onset of listerial infection. These findings point to a regulatory role of CD1-reactive cells in the immune response against listeriosis.

Effect of transforming growth factor beta on experimental Salmonella typhimurium infection in mice

We have investigated the effect of the in vivo administration of recombinant transforming growth factor beta (rTGF-beta) on the pathogenic mechanisms involved in Salmonella typhimurium experimental infection in mice. The protective response elicited by macrophages was induced by rTGF-beta1 by 2 days after experimental infection, as demonstrated by an increased NO production, while the humoral protective effect began with cytokine mRNA expression 2 days after the challenge and continued after 5 days with cytokine release and lymphocyte activation. We demonstrated that all mice who received rTGF-beta1 survived 7 days after infection. The number of bacteria recovered in the spleens and in the livers of rTGF-beta1-treated mice 2 and 5 days after infection was significantly smaller than that found in the same organs after phosphate-buffered saline (PBS) inoculation. Furthermore, 2 and 5 days after infection, splenic macrophages from rTGF-beta1-treated mice showed a greater NO production than did those from PBS-treated mice. The effect of rTGF-beta1 on S. typhimurium infection in mice was correlated with the expression of cell costimulatory CD28 molecules. Five days after S. typhimurium infection, the percentage of CD28(+)-expressing T cells in splenic lymphocytes from rTGF-beta1-treated mice increased with respect to that from control mice. Gamma interferon (IFN-gamma) mRNA was present in a greater amount in spleen cells from rTGF-beta1-treated mice after 2 days, although the intensity of the band decreased 5 days after the challenge. A similar pattern was obtained with the mRNAs for interleukin-1alpha (IL-1alpha), IL-6, TGF-beta, and inducible nitric oxide synthase, which showed greater expression in cells obtained from rTGF-beta1-treated and S. typhimurium-infected mice 2 days after challenge. The treatment with rTGF-beta1 induced an increase in IL-1alpha and IFN-gamma release in the supernatant of splenocyte cultures 5 days after the experimental infection with S. typhimurium. Moreover, we demonstrated that 5 days after infection, the IFN-gamma titer was significantly greater in the sera of rTGF-beta-treated mice than in those of PBS-treated mice. Also, hsp60 showed greater expression 2 days after the challenge in splenocytes from rTGF-beta1-treated mice. The role played by proinflammatory and immunoregulatory cytokines and by CD28 is discussed.

The Importance of TGF-β in Murine Visceral Leishmaniasis

IFN-γ is critical for the cure of leishmaniasis in humans and mice. BALB/c mice are genetically susceptible to infection with the visceralizing species of Leishmania, L. chagasi. We have evidence that a soluble factor(s) inhibits IFN-γ production by cultured liver granuloma cells from BALB/c mice during L. chagasi infection. In contrast, liver granulomas from C3H.HeJ mice, which are genetically resistant to L. chagasi infection, produce abundant IFN-γ. According to ELISAs and neutralization studies, there was not evidence that the Th2-type cytokines IL-10 or IL-4 contributed to IFN-γ suppression. However, both Ab neutralization and immunohistochemistry showed that granuloma-derived TGF-β was, at least in part, responsible for inhibiting IFN-γ release by CD4+ cells in BALB/c liver granuloma cultures. Consistently, TGF-β levels were high in liver granulomas from susceptible BALB/c mice but low in resistant C3H mice or in BALB/c mice that were immunized against L. chagasi disease. Administration of recombinant adenovirus expressing TGF-β (AdV-TGFβ) but not IL-10 (AdV-IL10) caused genetically resistant C3H mice to become significantly more susceptible to L. chagasi infection. In contrast, either AdV-TGFβ or AdV-IL10 could abrogate the protective immune response achieved by immunization of BALB/c mice. We conclude that locally secreted TGF-β inhibits Th1-associated cure of murine visceral leishmaniasis caused by L. chagasi, independently of Th2-type cytokines.

Ambiguous role of interleukin-12 in Yersinia enterocolitica infection in susceptible and resistant mouse strains

Endogenous interleukin-12 (IL-12) mediates protection against Yersinia enterocolitica in C57BL/6 mice by triggering gamma interferon (IFN-gamma) production in NK and CD4+ T cells. Administration of exogenous IL-12 confers protection against yersiniae in Yersinia-susceptible BALB/c mice but exacerbates yersiniosis in resistant C57BL/6 mice. Therefore, we wanted to dissect the different mechanisms exerted by IL-12 during Yersinia infections by using different models of Yersinia-resistant and -susceptible mice, including resistant C57BL/6 mice, susceptible BALB/c mice, intermediate-susceptible wild-type 129/Sv mice, 129/Sv IFN-gamma-receptor-deficient (IFN-gamma R-/-) mice and C57BL/6 tumor necrosis factor (TNF) receptor p55 chain-deficient (TNFR p55-/-) mice. IFN-gamma R-/- mice turned out to be highly susceptible to infection by Y. enterocolitica compared with IFN-gamma R+/+ mice. Administration of IL-12 was protective in IFN-gamma R+/+ mice but not in IFN-gamma R-/- mice, suggesting that IFN-gamma R-induced mechanisms are essential for IL-12-induced resistance against yersiniae. BALB/c mice could be rendered Yersinia resistant by administration of anti-CD4 antibodies or by administration of IL-12. In contrast, C57BL/6 mice could be rendered more resistant by administration of transforming growth factor beta (TGF-beta). Furthermore, IL-12-triggered toxic effects in C57BL/6 mice were abrogated by coadministration of TGF-beta. While administration of IL-12 alone increased TNF-alpha levels, administration of TGF-beta or TGF-beta plus IL-12 decreased both TNF-alpha and IFN-gamma levels in Yersinia-infected C57BL/6 mice. Moreover, IL-12 did not induce toxicity in Yersinia-infected TNFR p55-/- mice, suggesting that TNF-alpha accounts for IL-12-induced toxicity. Taken together, IL-12 may induce different effector mechanisms in BALB/c and C57BL/6 mice resulting either in protection or exacerbation. These results are important for understanding the critical balance of proinflammatory and regulatory cytokines in bacterial infections which is decisive for beneficial effects of cytokine therapy.