Search

The search for the encephalitogenic factor driving pathogenic T cells in autoimmune diseases such as rheumatoid arthritis, multiple sclerosis (MS), and psoriasis has proven to be a long and difficult mission, which is not yet completed. In this issue of the European Journal of Immunology, the importance of the transcription factor T-bet, previously shown to be essential for the induction of autoimmune disease in mice, is challenged. Two independent groups, O'Connor et al. [Eur. J. Immunol. 2013. 43:2818-2823] report] and Grifka-Walk et al. [Eur. J. Immunol. 2013. 43:2824-2831], report that T-bet is not mandatory for T cells to cause experimental autoimmune encephalomyelitis ( EAE), which serves as a paradigmatic T-cell-mediated autoimmune disease. Both groups found that T-bet KO mice were fully susceptible to develop EAE, both after immunization with self-antigen and after adoptive transfer of IL-23-polarized autoaggressive T cells. T-bet deficiency mediated the loss of IFN-γ expression but retained or even enhanced GM- CSF and IL-17 production by central nervous system ( CNS)-infiltrating T cells. These findings indicate that we have lost the last transcriptional regulator previously held to be required for the generation of autoimmune pathogenic T cells. [ABSTRACT FROM AUTHOR]

Extracellular attaching and effacing (A/E) pathogens including pathogenic Escherichia coli colonize the host gut causing diarrhea and inflammation. Although much is known regarding the pathogenesis of A/E bacteria, there remains an incomplete understanding of host immune responses to these microbes. NK cells are an important source of IFN-γ and are essential for early innate responses to viral pathogens; however, their role during extracellular bacterial infections is still largely unexplored. We studied the host response to the murine A/E pathogen Citrobacter rodentium to investigate NK-cell function during infection. NK1.1+ cell depletions and analysis of colonic intestinal inflammation following Citrobacter infection demonstrated that CD3−NK1.1+ cells play an important role in the initial clearance of C. rodentium, as evidenced by higher bacterial load, intestinal pathology, and crypt hyperplasia at the peak of inflammation in depleted mice. Loss of CD3−NK1.1+ cells resulted in lower colonic IFN-γ, TNF-α, and IL-12, and a delay in homing of IFN-γ+CD4+ T cells to the gut. Loss of this response resulted in lower anti- C. rodentium IgG in NK1.1-depleted mice. These data establish that CD3−NK1.1+ cells are critical for inducing an early Th1 response involved in clearance of a pathogen that is restricted to the gastrointestinal tract. [ABSTRACT FROM AUTHOR]

CD4+ T-cell help for B cells is crucial for effective Ab responses. Although follicular T helper (Tfh) cells have emerged as the main providers of T-cell help to B lymphocytes during the germinal center reaction, much less is known about the helper capacities of other effector CD4+ T cells. The purpose of the present study was to evaluate the acquisition of B-cell help capacity of canonically derived T helper 2 (Th2) cells, a Th-cell subset originally considered responsible for B-cell help in vivo. We demonstrate herein that developing Th2 cells in mice co-express activated forms of signal transducer and activator of transcription 6 (STAT6) and STAT3 and that STAT3 expression was required for the capacity of Th2 cells to provide B-cell help. Thus, Th2 lymphocytes share a common, STAT3-mediated activation program for the acquisition of optimal B-cell help capacity with Tfh cells. Moreover, the expression of STAT3 in Th2 cells enhanced the IgG1-to-IgE class switch ratio in vivo, a finding with important implications for understanding the molecular basis of allergic diseases. [ABSTRACT FROM AUTHOR]

MIF and its receptor, CD74, are pivotal regulators of the immune system. Here, we demonstrate for the first time that partial MHC class II constructs comprised of linked β1α1 domains with covalently attached antigenic peptides (also referred to as recombinant T-cell receptor ligands - RTLs) can inhibit MIF activity by not only blocking the binding of rh MIF to immunopurified CD74, but also downregulating CD74 cell-surface expression. This bifunctional inhibition of MIF/ CD74 interactions blocked downstream MIF effects, including enhanced secretion of proinflammatory cytokines, anti-apoptotic activity, and inhibition of random migration that all contribute to the reversal of clinical and histological signs of EAE. Moreover, we demonstrate that enhanced CD74 cell-surface expression on monocytes in mice with EAE and subjects with multiple sclerosis can be downregulated by humanized RTLs, resulting in reduced MIF binding to the cells. Thus, binding of partial MHC complexes to CD74 blocks both the accessibility and availability of CD74 for MIF binding and downstream inflammatory activity. [ABSTRACT FROM AUTHOR]

Human native milk lactoferrin ( LF) and recombinant forms of lactoferrin (r LF) are available with identical aa sequences, but different glycosylation patterns. Native lactoferrin ( NLF) possesses the intrinsic ability to stimulate vigorous Ig G and Ig E antibody responses in BALB/c mice, whereas recombinant forms ( Aspergillus or rice) are 40-fold less immunogenic and 200-fold less allergenic. Such differences are independent of endotoxin or iron content and the glycans do not contribute to epitope formation. A complex glycoprofile is observed for NLF, including sialic acid, fucose, mannose, and Lewis ( Le)x structures, whereas both r LF species display a simpler glycoprofile rich in mannose. Although Lex type sugars play a Th2-type adjuvant role, endogenous expression of Lex on NLF did not completely account for the more vigorous Ig E responses it provoked. Furthermore, coadminstration of r LF downregulated Ig E and upregulated IgG2a antibody responses provoked by NLF, but was without effect on responses to unrelated peanut and chicken egg allergens. These results suggest glycans on r LF impact the induction phase to selectively inhibit Ig E responses and that differential glycosylation patterns may impact on antigen uptake, processing and/or presentation, and the balance between Th1 and Th2 responses. [ABSTRACT FROM AUTHOR]

Recently, we identified the CD20 homolog Ms4a8a as a novel molecule expressed by tumor-associated macrophages that directly enhances tumor growth. Here, we analyzed Ms4a8a+ macrophages in M2-associated infectious pathologies. In late-stage Trypanosoma congolense and Taenia crassiceps infections, Ms4a8a expression was detected in hepatic and peritoneal macrophages respectively. Innate immunity in these infections is modulated by Toll-like receptor ( TLR) signaling and TLR2/4/7 agonists strongly induced Ms4a8a expression in bone marrow derived macrophages ( BMDMs) treated with M2 mediators (glucocorticoids/ IL-4). LPS/dexamethasone/ IL-4-induced Ms4a8a+ BMDMs were characterized by strong expression of m RNA of mannose receptor ( Mmr), arginase 1, and CD163, and by decreased i NOS expression. Coinduction of Ms4a8a by M2 mediators and TLR agonists involved the classical TLR signaling cascade via activation of My D88/ TRIF and NF-κ B. Forced overexpression of Ms4a8a modulated the TLR4 response of RAW264.7 cells as shown by gene expression profiling. Upregulation of Hdc, Tcfec, and Sla was confirmed both in primary LPS/dexamethasone/ IL-4-stimulated Ms4a8a+ BMDMs and in peritoneal macrophages from late-stage Taenia crassiceps infection. In conclusion, we show that TLR signaling skews the typical alternative macrophage activation program to induce a special M2-like macrophage subset in vitro that also occurs in immunomodulatory immune reactions in vivo, a process directly involving the CD20 homolog Ms4a8a. [ABSTRACT FROM AUTHOR]

Foxp3+ regulatory T (Treg) cells modulate the functions of multiple immune cell types, and loss of Treg cells causes lethal, CD4+ T-cell-dependent multiorgan autoimmune disease in both mice and humans. However, how different effector T-cell subets contribute to the severe autoimmunity observed in the absence of Treg cells remains controversial. We found that although expanded populations of Th1, Th2, and Th17 cells can be detected in scurfy ( sf) mice, Th1 cells predominate. Moreover, using a genetic approach, we found that sf mice with deficiencies in type-1 immunity ( sf × Ifngr1−/−, sf × Tbx21−/−, and sf × Ifngr1−/− /Tbx21−/−) have an extended lifespan that is associated with altered cytokine production and attenuated cutaneous and hepatic inflammation. By contrast, sf mice deficient in type-2 immune responses ( sf × Stat6−/−) display a significantly reduced lifespan with increased hepatic inflammation, but decreased dermatitis. These data indicate that Th1 cells and their associated cytokines drive early immunopathology in Foxp3-deficient sf mice, highlighting the essential role of Treg cells in restraining Th1-cell-mediated autoimmunity. [ABSTRACT FROM AUTHOR]

In schistosomiasis, the severity of CD4+ T-cell-mediated hepatic granulomatous inflammation against parasite eggs varies considerably in humans and among mouse strains. In C57BL/6 mice, pronounced exacerbation of immunopathology induced by immunization with schistosome egg Ag in CFA (SEA/CFA) substantially recapitulates the natural high pathology seen in CBA mice; both are associated with a significant elevation of Th17- and Th1-cell-derived proinflammatory cytokines. We now investigated the relative contribution of the effector cytokines IL-17 and IFN-γ in pathology development of 7 wk-infected, SEA/CFA-immunized, IL-17−/−, IFN-γ−/−, and IL-17/IFN-γ−/− mice. In IL-17−/− mice there was significant reduction of immunopathology despite increased levels of IFN-γ, whereas in IFN-γ−/− mice, markedly exacerbated immunopathology correlated with an increase in IL-17. In IL-17/IFN-γ−/− mice, complete resistance to SEA/CFA-induced disease exacerbation was associated with a reduction in IL-23p19, IL-1β, CXCL1 and iNOS, and with an increase in IL-5, IL-10 and Relmα. IL-17 and IFN-γ were derived from distinct CD4+ T cells in which production of each cytokine was suppressed by the other. Our results indicate that severe immunopathology in murine schistosomiasis is mainly driven by IL-17 and regulated by IFN-γ; however, in the absence of IL-17, IFN-γ is capable of exerting a limited, yet significant, pathogenic function. [ABSTRACT FROM AUTHOR]

Murine Foxp3 [ABSTRACT FROM AUTHOR]

Oral antigen uptake can induce systemic immune responses ranging from tolerance to immunity. However, the underlying mechanisms are poorly understood, especially in humans. Here, keyhole limpet hemocyanin (KLH), a neoantigen which has been used in earlier studies of oral tolerance, was fed in a repeated low-dose and a single high-dose protocol to healthy volunteers. KLH-specific CD4 [ABSTRACT FROM AUTHOR]

Leishmania (Viannia) organisms are the most prevalent etiologic agents of human cutaneous leishmaniasis in the Americas. Nevertheless, our knowledge of the immunological mechanisms exploited by L. (Viannia) organisms remains limited and the mechanisms underlying disease are not well understood. Here, we report the development of a BALB/c mouse model of L. (V.) panamensis infection that is able to reproduce chronic disease, with persistent infection and clinically evident lesions for over 1 year. The immune response of the mouse resembles that found for L. (V.) panamensis-infected patients with chronic and recurrent lesions, presenting a mixed Th1/Th2 response with the presence of TNF-α, IFN-γ, IL-10 and IL-13. Using immunodeficient mice, the critical role for IL-13 and/or IL-4Rα in determining susceptibility to chronic infection was evident. With the induction of healing in the immunodeficient mice, increases in IFN-γ and IL-17 were found, concomitant with parasite control and elimination. Specifically, increases in CD4 [ABSTRACT FROM AUTHOR]

Host resistance to Leishmania major is highly dependent on the development of a Th1 immune response. The TLR adaptator myeloid differentiation protein 88 (MyD88) has been implicated in the Th1 immune response associated with the resistant phenotype observed in C57BL/6 mice after infection with L. major. To investigate whether the MyD88 pathway is differentially used by distinct substrains of parasites, MyD88 [ABSTRACT FROM AUTHOR]

The classical reaction of the host to helminth infections is the induction of Th2 immune responses with a regulatory component. DC, as central players in the induction and maintenance of immune responses, play a prominent role in both these processes, and in recent years considerable progress has been made in elucidating the mechanisms behind the interplay between DC and helminths. It is becoming increasingly clear that helminths modulate DC function not only via direct interactions but also indirectly via host-derived cues. Furthermore, while studies have until recently focused on receptor signaling-mediated DC modulation by helminths, evidence is emerging that DC may also respond to helminth infections by sensing stress signals or tissue damage inflicted by the worms or their products. Here, we will discuss these new insights and will link them to the origin and importance of Th2 and regulatory immune responses with respect to the survival of both parasite and host. [ABSTRACT FROM AUTHOR]

Compared with cutaneous leishmaniasis, vaccination against visceral leishmaniasis has received limited attention. Most available drugs are toxic, and relapse after cure remains a chronic problem. Growing limitations in available chemotherapeutic strategies due to emerging resistant strains and lack of an effective vaccine strategy against visceral leishmaniasis deepens the crisis. Complete soluble antigen (CSA), from a β1-4 galactosyltransferase expressing attenuated Leishmania donovani parasite, induced protection against subsequent challenge and during active infections. CSA immunization was effective against both pentavalent antimony sensitive and resistant strains of L. donovani. Majority (∼85%) of the immunized animals showed sterile protection. Resolution of the disease required the presence of T cells, and the recovered animals remained immune to re-challenge. Control of the parasites was dependent on type 1 CD4 [ABSTRACT FROM AUTHOR]

IFN regulatory factor 7 (IRF7) has been described as the master regulator of type I IFN responses and has been shown to be critical for innate antiviral immunity in vivo. In addition to type I IFN, NK cell responses are involved in the control of viral replication during acute viral infection. To investigate the role of IRF7 in the context of a viral infection that induces a strong NK cell response, the murine cytomegalovirus (MCMV) infection model was used. WT, IRF7-deficient and IRF3/IRF7-double deficient mice were infected with MCMV. The systemic IFN-α response to MCMV was entirely dependent on IRF7, but independent of IRF3. However, peak IFN-β production during MCMV infection was not affected by the lack of IRF7 or both IRF7 and IRF3. Despite the complete lack of IFN-α production IRF7- and IRF3/IRF7-deficient mice were surprisingly efficient in controlling MCMV replication and were only modestly more susceptible to MCMV infection than WT mice. NK cell cytotoxicity was unimpaired and NK cell IFN-γ production was enhanced in IRF7-deficient mice correlating with increased levels of bioactive IL-12. Owing to these compensatory mechanisms IRF7-dependent antiviral immune responses were not essential for resistance against acute MCMV infection in vivo. [ABSTRACT FROM AUTHOR]

IL-1 null mice are unable to expel the intestinal nematode Trichuris muris; whereas WT littermates exhibit sterile immunity. Intriguingly the essential signalling components IL-1R1 and IL-1R accessory protein (AcP) are dispensable for expulsion of this parasite. IL-1 is thus critical for CD4 Th2-mediated immunity to T. muris; however, this action is independent of the established IL-1 signalling receptor. We also present data demonstrating that both IL-1α and IL-1β induce measurable effects on T. muris primed cells isolated from IL-1R1 or IL-1R AcP null mice. MLN cells from these mice restimulated with parasite antigen proliferated at a greater rate and produced more cytokines in response to exogenous IL-1. This ability to respond to IL-1 was restricted to these parasite-primed cells and importantly was not evident in cells from naïve gene null mice. These in vitro data are consistent with the observed ability of mice with compromised IL-1 signalling to expel the parasite, bolstering the premise that an alternative IL-1 signalling mechanism is accessible in the context of an intestinal helminth-driven Th2 immune response. [ABSTRACT FROM AUTHOR]

CTLA-4 has potent regulatory effects on the threshold of T-cell signalling and, in the process, guards against the development of hyper-proliferation and autoimmunity. Despite this, the role of CTLA-4 on specific T-cell subsets has been unclear. Such studies could shed light on both the function of CTLA-4, and on the contribution of the subsets to the disease phenotype of the Ctla4 mouse. Recently, a role for this co-receptor in the function of Treg has been outlined and, in this issue of the European Journal of Immunology, the selective targeting of the T-box transcription factor Eomes by CTLA-4 in the regulation of CD8 cytolytic T-cell (CTL) effector function is shown. Together, these papers shed light on the role of CTLA-4 in different T-cell subsets. [ABSTRACT FROM AUTHOR]

CD8 T lymphocytes are required for effective host defense against pathogens and also for mediating effector responses against uncontrolled proliferating self-tissues. In this study, we determine that individual CD8 T cells are tightly controlled in their effector functions by CD152 (CTLA-4). We demonstrate that signals induced by CD152 reduce the frequency of IFN-γ and granzyme B expressing CD8 T cells independently of the transcription factors T-bet or cKrox by selectively inhibiting accumulation of Eomesodermin mRNA and protein. Ectopic expression of Eomesodermin reversed the CD152-mediated inhibition of effector molecule production. Additionally, enhanced cytotoxicity of individual CD8 T cells differentiated in the absence of CD152 signaling was determined in vivo. These novel insights extend our understanding of how immune responses of CD8 T cells are selectively modulated. [ABSTRACT FROM AUTHOR]

Galectin-3 is a β-galactoside-binding lectin implicated in the fine-tuning of innate immunity. Rhodococcus equi, a facultative intracellular bacterium of macrophages, causes severe granulomatous bronchopneumonia in young horses and immunocompromised humans. The aim of this study is to investigate the role of galectin-3 in the innate resistance mechanism against R. equi infection. The bacterial challenge of galectin-3-deficient mice (gal3) and their wild-type counterpart (gal3) revealed that the LD for the gal3 mice was about seven times higher than that for the gal3 mice. When challenged with a sublethal dose, gal3 mice showed lower bacteria counts and higher production of IL-12 and IFN-γ production, besides exhibiting a delayed although increased inflammatory reaction. Gal3 macrophages exhibited a decreased frequency of bacterial replication and survival, and higher transcript levels of IL-1β, IL-6, IL-10, TLR2 and MyD88. R. equi-infected gal3 macrophages showed decreased expression of TLR2, whereas R. equi-infected gal3 macrophages showed enhanced expression of this receptor. Furthermore, galectin-3 deficiency in macrophages may be responsible for the higher IL-1β serum levels detected in infected gal3 mice. Therefore galectin-3 may exert a regulatory role in innate immunity by diminishing IL-1β production and thus affecting resistance to R. equi infection. [ABSTRACT FROM AUTHOR]

Various infections sensitize to lethal shock by promoting hyperactivation of macrophages to LPS stimulation. Although macrophages are thought to be deactivated upon contact with apoptotic cells during Trypanosoma cruzi infection, T. cruzi infection also sensitizes mice to endotoxemia. Herein, we studied the mechanisms of sensitization to endotoxemia in T. cruzi-infected mice in order to solve the paradox. Live (but not fixed) trypomastigotes from various stocks sensitized mice to endotoxemia. Mice deficient in glycolipid recognition (TLR2 and CD1d) were sensitized by infection to challenge with LPS. Infected mice hyperproduced TNF and IL-10 upon LPS challenge. Infected TNF-R1, macrophage migration inhibitory factor (MIF) and IFN-γ mice were lethally sensitized, but infected TNF-R1 mice administered anti-MIF survived shock with LPS. Macrophages from infected mice hyperproduced TNF in response to LPS stimulation and displayed increased expression of TLR4 compared to non-infected controls. Treatment with the PGE synthesis inhibitor acetylsalicylic acid (AAS) in vivo reduced parasitemia and enhanced LPS-stimulated production of TNF by macrophages, but the effect was less in infected mice than in normal mice. Nevertheless, AAS treatment did not increase the susceptibility of infected mice to sublethal shock with LPS. Our results point to independent MIF and TNF/TNF-R1 lethal pathways and suggest a role for hyperactivated macrophages in T. cruzi-sensitized LPS-induced shock. [ABSTRACT FROM AUTHOR]

Natural killer (NK) cells play a crucial role in the initial response to viral infections but the mechanisms controlling their activation are unclear. We show a rapid and transient activation of NK cells that results in the production of IFN-γ immediately following infection with herpes simplex virus type 1 (HSV-1). Activation of NK cells leading to synthesis of IFN-γ was not mediated by a direct interaction with virus but required the presence of additional cell types and was largely dependent on the cytokine IL-18, but not IL-12. HSV-1-induced IFN-γ expression by NK cells in vitro was impaired in spleen cultures depleted of CD11c cells. Conversely, coculture of NK cells with virus-exposed conventional DC or plasmacytoid (p)DC restored the production of IFN-γ, indicating that multiple DC subsets could mediate NK cell activation. While conventional DC populations stimulated NK cells independently of IL-18, they were less effective than pDC in promoting NK cell IFN-γ expression. In contrast, the potent stimulation of NK cells by pDC was dependent on IL-18 as pDC from IL-18-deficient mice only activated a similar proportion of NK cells as conventional DC. These data identify IL-18 as a crucial factor for pDC-mediated NK cell regulation. [ABSTRACT FROM AUTHOR]

The molecular mechanisms that suppress Th1 immune responses in pregnancy are unknown. We assessed the expression of the Th1 cytokine transcription factor T-bet. We isolated PBMC and T cells from non-pregnant and pregnant women and demonstrated that T-bet is specifically down-regulated in pregnancy under basal and stimulated conditions. Low levels of T-bet protein were detected in the nuclear fraction of unstimulated PBMC from non-pregnant, but not pregnant women. Nuclear levels of T-bet increased in response to PMA/ionomycin in PBMC from non-pregnant, but not pregnant women. T-bet expression was greater in whole cell lysates of stimulated CD3 T cells from non-pregnant relative to pregnant women. NF-κB is specifically down-regulated in T cells in pregnant women, resulting in suppressed expression of Th1 cytokines IL-2, IFN-γ and TNF-α. In this study, down-regulation of NF-κB also resulted in diminished expression of T-bet. PMA induces NF-κB translocation, T-bet expression and IL-2, IFN-γ and TNF-α production. Conversely, pre-incubation with SN50, and NF-κB oligodeoxyribonucleotide decoys suppressed PMA-induced NF-κB translocation and gene transcription, respectively, resulting in diminished T-bet expression and Th1 cytokine production. Therefore, maintenance of the cytokine environment for pregnancy success is mediated via strict regulation of Th1 immune responses, more specifically through control of NF-κB and T-bet transcription. [ABSTRACT FROM AUTHOR]

Macrophage migration inhibitory factor (MIF) is increased in asthmatic patients and plays a critical role in the pathogenesis of asthma. We show here that mice lacking MIF failed to develop airway hyper-responsiveness (AHR), tissue eosinophilia, and mucus metaplasia. Analysis of the bronchoalveolar fluids revealed a substantial reduction of IL-13, eotaxin and cysteinyl-leukotrienes. The lack of these cardinal features of asthma in MIF mice occurs regardless of high concentrations of IL-4 in the lung and OVA-specific IgE in the serum. Antigen-specific lymphocyte proliferation and IL-13 production were similarly increased in the draining lymph nodes of OVA-immunized and challenged MIF mice compared to WT, but were reduced in the spleen of MIF, thus indicating differential roles of MIF in these compartments. Stimulation of naive CD4 cells with anti-CD3 antibody demonstrated that MIF cells produced increased amounts of IFN-γ and IL-4 compared to WT CD4 cells. Finally, treatment of sensitized BALB/c mice with neutralizing anti-MIF antibody abrogated the development of ARH and airway inflammation without affecting the production of Th2 cytokines or IgE. The present study demonstrates that MIF is required for allergic inflammation, adding important elements to our knowledge of asthma pathogenesis and suggesting that neutralization of MIF might be of therapeutic value in asthma. [ABSTRACT FROM AUTHOR]

Escherichia coli heat-labile enterotoxin (Etx) is an oral adjuvant in mice. We show that this is also true for rats. To understand this adjuvant activity we examined lymph dendritic cells (DC) migrating from the intestine to mesenteric lymph nodes (MLN) in animals fed Etx. These DC can prime antigen-specific antibody responses. We show that in rats the small intestine contains 7-24 million DC and 8 × 10of these migrate to MLN each day. Surprisingly, Etx does not stimulate increased migration of lymph DC. However, oral Etx affects the activation, antigen transport and localization of migratory DC. Specifically, expression of CD25 increases on the CD172a subset of lymph DC. Oral Etx also increases the number of CD172a lymph DC containing co-administered ovalbumin. CD172a lymph DC treated with Etx in vitro, or purified from the lymph of animals fed Etx, stimulate stronger proliferative responses from primed T cells. Etx also directs more of the CD172a lymph DC into the central region of the MLN T cell areas. This change in DC localization is associated with an increase in the expression of CCR7. These data help advance our understanding of the role of DC in initiating mucosal immune responses in vivo. [ABSTRACT FROM AUTHOR]

Lung pathology observed during influenza infection is due to direct damage resulting from viral replication and bystander damage caused by overly exuberant antiviral immune mechanisms. In the absence of universally effective vaccines and antiviral therapies, knowledge of the cellular components required for immune containment of influenza is essential. ICOS is a late co-stimulatory molecule expressed by T cells 12-24 h after activation. We show for the first time that inhibition of ICOS with a monoclonal antibody reduces pulmonary T cell inflammation and associated cytokine expression. Surprisingly however, this reduction in T cells was not accompanied by an alleviation of weight loss and illness. Furthermore, lung viral titres were elevated following anti-ICOS treatment, suggesting that the beneficial outcome of reducing T cell pathology was masked by enhanced virus-induced damage and innate inflammation. This study demonstrates the delicate balance that exists between pathogen burden and pulmonary T cell inflammation during influenza infection and highlights the critical role of ICOS in this response. [ABSTRACT FROM AUTHOR]

Leishmania donovani promastigotes evade the induction of a proinflammatory response during their invasion of naive macrophages. However, their entry into IFN-γ-primed macrophages is accompanied by the secretion of nitric oxide (NO) and proinflammatory cytokines. In the present study, we addressed the hypothesis that priming with IFN-γ induces the expression of a receptor that enables mouse macrophages to recognize L. donovani promastigotes. We observed that in IFN-γ-primed macrophages, L. donovani promastigotes stimulated Interleukin-1 receptor-associated kinase-1 (IRAK-1) activity. We next showed that Toll-like receptor (TLR)3 is barely detectable in naive macrophages but is expressed in IFN-γ-treated macrophages. Silencing of TLR3, TLR2, IRAK-1 and myeloid differentiation factor 88 (MyD88) expression by RNA interference revealed that both TLR are involved in the secretion of NO and TNF-α induced by L. donovani promastigotes. Using L. donovani mutants, we showed that TLR2-mediated responses are dependent on Galβ1,4Manα-PO-containing phosphoglycans, whereas TLR3-mediated responses are independent of these glycoconjugates. Furthermore, our data indicate a participation of TLR2 and TLR3 in the phagocytosis of L. donovani promastigotes and a role for TLR3 in the leishmanicidal activity of the IFN-γ-primed macrophages. Collectively, our data are consistent with a model where recognition of L. donovani promastigotes depends on the macrophage activation status and requires the expression of TLR3. [ABSTRACT FROM AUTHOR]

T-bet is an important Th1 driving transcription factor regulated by IFN-γ/STAT1 pathway. T-bet turns on IFN-γ transcription in CD4 T cells and T-bet-deficient cells fail to differentiate to Th1 direction. Previous reports have characterized function of T-bet mainly in murine cells and very little is known about its functions in human cells. Here, we studied T-bet expression kinetics in parallel with GATA3 during Th1/Th2 polarization. We demonstrate that in addition to CD3/CD28 activation, cytokines IL-12 and IFN-α in the presence of neutralizing anti-IFN-γ enhanced T-bet mRNA and protein expression in human CD4 cells. T-bet is known to be a potent inducer of IFN-γ. Even though IFN-γ and IL-12 stimulation induced similar levels of T-bet protein in human CD4 cells, IFN-γ-treated cells produced considerably less IFN-γ than cells treated with IL-12. Therefore, high T-bet protein expression does not necessarily correlate with IFN-γ production. In addition, we show that the immunosuppressive cytokine TGF-β inhibits T-bet and GATA3 protein expression only if it is present prior to primary T cell activation and is maintained in the cultures during the early polarization of Th1/Th2 cells. In conclusion, we report new insights into the cytokine regulation of T-bet in human CD4 T cells. [ABSTRACT FROM AUTHOR]