Orphan nuclear receptor NR4A2 expressed in T cells from multiple sclerosis mediates production of inflammatory cytokines

Multiple sclerosis (MS) is an autoimmune disease of the central nervous system (CNS) mediated by Th17 and Th1 cells. DNA microarray analysis previously showed that NR4A2, an orphan nuclear receptor, is strongly up-regulated in the peripheral blood T cells of MS. Here, we report that NR4A2 plays a pivotal role for mediating cytokine production from pathogenic T cells. In experimental autoimmune encephalomyelitis (EAE), an animal model of MS, NR4A2, was selectively up-regulated in the T cells isolated from the CNS. Strikingly, a forced expression of NR4A2 augmented promoter activities of IL-17 and IFN-gamma genes, leading to an excessive production of these cytokines. Conversely, treatment with siRNA for NR4A2, resulted in a significant reduction in the production of IL-17 and IFN-gamma. Furthermore, treatment with NR4A2 siRNA reduced the ability of encephalitogenic T cells to transfer EAE in recipient mice. Thus, NR4A2 is an essential transcription factor for triggering the inflammatory cascade of MS/EAE and may serve as a therapeutic target.

Tumor-specific Th17-polarized cells eradicate large established melanoma

CD4+ T cells can differentiate into multiple effector subsets, but the potential roles of these subsets in anti-tumor immunity have not been fully explored. Seeking to study the impact of CD4+ T cell polarization on tumor rejection in a model mimicking human disease, we generated a new MHC class II-restricted, T-cell receptor (TCR) transgenic mouse model in which CD4+ T cells recognize a novel epitope in tyrosinase-related protein 1 (TRP-1), an antigen expressed by normal melanocytes and B16 murine melanoma. Cells could be robustly polarized into Th0, Th1, and Th17 subtypes in vitro, as evidenced by cytokine, chemokine, and adhesion molecule profiles and by surface markers, suggesting the potential for differential effector function in vivo. Contrary to the current view that Th1 cells are most important in tumor rejection, we found that Th17-polarized cells better mediated destruction of advanced B16 melanoma. Their therapeutic effect was critically dependent on interferon-gamma (IFN-gamma) production, whereas depletion of interleukin (IL)-17A and IL-23 had little impact. Taken together, these data indicate that the appropriate in vitro polarization of effector CD4+ T cells is decisive for successful tumor eradication. This principle should be considered in designing clinical trials involving adoptive transfer-based immunotherapy of human malignancies.

Interleukin (IL)-23 receptor is a major susceptibility gene for Graves' ophthalmopathy: the IL-23/T-helper 17 axis extends to thyroid autoimmunity

CONTEXT

IL-23 and its receptor (IL-23R) guide T cells toward the T-helper 17 phenotype. IL-23R single nucleotide polymorphisms (SNPs) have been associated with several autoimmune diseases, including Crohn's disease and rheumatoid arthritis.

OBJECTIVE

Our objective was to determine whether variants in the IL-23R gene are associated with Graves' disease (GD) and Graves' ophthalmopathy (GO).

DESIGN AND PARTICIPANTS

A total of 216 North American Caucasian GD patients and 368 healthy controls were genotyped for four SNPs spanning the IL-23R gene. SNPs rs11209026 and rs7530511 were genotyped using the TaqMan allelic discrimination assays (Applied Biosystems, Foster City, CA), and SNPs rs2201841 and rs10889677 were genotyped using a fluorescent-based restriction fragment length polymorphism method.

RESULTS

The A allele of rs2201841 was present in 78.8% of GD patients with GO and 64.7% of controls [P=1.1x10(-4); odds ratio (OR)=2.04]; the AA genotype was also significantly increased in GO patients compared with controls (62.5 and 41%, respectively; P=1.0x10(-4); OR=2.4). The C allele of rs10889677 was present in 78.6% of GO patients and 64.5% of controls (P=1.3x10(-4); OR=2.03), and the CC genotype was also significantly increased in GO patients vs. controls (62.1 and 41.0%, respectively; P=1.4x10(-4); OR=2.36). The TT genotype of rs7530511 was significantly associated with GD, but not specifically with GO; it was present in 2.5% of GD patients and 0.3% of controls (P=0.02; OR=9.4). The rs11209026 SNP, which is the most strongly associated with Crohn's disease, was not associated with GD or GO in our data set.

CONCLUSIONS

Variants in the IL-23R gene are strongly associated with GO. These variants may predispose to GO by changing the expression and/or function of IL-23R, thereby promoting a proinflammatory signaling cascade.

Th17 cells: effector T cells with inflammatory properties

Upon activation, naïve CD4(+) T cells differentiate into effector T cells with specific effector functions and cytokine profiles. The Th1/Th2 paradigm has recently been reevaluated to include a third population of T helper cells, producing IL-17 and designated Th17. The differentiation of Th17 cells requires the coordinate and specific action of the proinflammatory cytokine IL-6 and the immunosuppressive cytokine TGF-beta. In addition, the IL-12 family member IL-23 is involved in the maintenance of these cells. Analogous to other T helper cell subsets, Th17 commitment is initiated by sequential involvement of STAT molecules, i.e. STAT3 downstream of cytokine receptors, and specific transcription factors, i.e. ROR-gammat. Recent data also support the existence of a complex network of cytokines regulating Th17 cells. Clearly, the specific effector functions of Th17 cells expand beyond previously described effects of Th1 and Th2 immunity, with specific roles in host defense against certain pathogens and in organ-specific autoimmunity. The potential dynamics of Th17 cell populations and their interplay with other inflammatory cells in the induction of tissue inflammation in host defense and organ-specific autoimmunity are discussed.

Resistance to experimental autoimmune encephalomyelitis and impaired T cell priming by dendritic cells in Src homology 2 domain-containing protein tyrosine phosphatase substrate-1 mutant mice

Src homology 2 domain-containing protein tyrosine phosphatase (SHP) substrate-1 (SHPS-1) is a transmembrane protein that binds the protein tyrosine phosphatases SHP-1 and SHP-2 through its cytoplasmic region and is expressed on the surface of CD11c(+) dendritic cells (DCs) and macrophages. In this study, we show that mice that express a mutant form of SHPS-1 lacking most of the cytoplasmic region are resistant to experimental autoimmune encephalomyelitis (EAE) in response to immunization with a peptide derived from myelin oligodendrocyte glycoprotein (MOG (35-55)). The MOG (35-55)-induced proliferation of, and production of IFN-gamma, IL-2, and IL-17, by T cells from immunized SHPS-1 mutant mice were reduced compared with those apparent for wild-type cells. The abilities of splenic DCs from mutant mice to stimulate an allogenic MLR and to prime Ag-specific T cells were reduced. Both IL-12-stimulated and TLR-dependent cytokine production by DCs of mutant mice were also impaired. Finally, SHPS-1 mutant mice were resistant to induction of EAE by adoptive transfer of MOG (35-55)-specific T cells. These results show that SHPS-1 on DCs is essential for priming of naive T cells and the development of EAE. SHPS-1 is thus a potential therapeutic target in inflammatory disorders of the CNS and other autoimmune diseases.

Kaempferol Inhibits IL-4-Induced STAT6 Activation by Specifically Targeting JAK3

IL-4 is involved in several human diseases including allergies, autoimmunity, and cancer. Its effects are mainly mediated through the transcription factor STAT6. Therefore, investigation of compounds that regulate STAT6 activation is of great interest for these diseases. Natural polyphenols are compounds reported to have therapeutic properties in diseases involving IL-4 and STAT6. The aim of this study was to investigate the effect of these compounds in the activation of this transcription factor. We found that in hemopoietic cells from human and mouse origin, some flavonoids were able to inhibit the activation of STAT6 by IL-4. To identify molecular mechanisms, we focused on kaempferol, the compound that showed the greatest inhibitory effect with the lowest cell toxicity. Treatment of cells with kaempferol did not affect activation of Src kinase by IL-4 but did prevent the phosphorylation of JAK1 and JAK3. Further enzymatic analysis demonstrated that kaempferol blocked the in vitro phosphorylation activity of JAK3 without affecting JAK1, suggesting that it specifically targeted JAK3 activity. Accordingly, kaempferol had no effect on STAT6 activation in nonhemopoietic cell lines lacking JAK3, supporting its selective inhibition of IL-4 responses through type I receptors expressing JAK3 but not type II lacking this kinase. The inhibitory effect of kaempferol was also observed in IL-2 but not IL-3-mediated responses and correlated with the inhibition of MLC proliferation. These findings reveal the potential use of kaempferol as a tool for selectively controlling cell responses to IL-4 and, in general, JAK3-dependent responses.

Type II monocytes modulate T cell-mediated central nervous system autoimmune disease

Treatment with glatiramer acetate (GA, copolymer-1, Copaxone), a drug approved for multiple sclerosis (MS), in a mouse model promoted development of anti-inflammatory type II monocytes, characterized by increased secretion of interleukin (IL)-10 and transforming growth factor (TGF)-beta, and decreased production of IL-12 and tumor necrosis factor (TNF). This anti-inflammatory cytokine shift was associated with reduced STAT-1 signaling. Type II monocytes directed differentiation of T(H)2 cells and CD4+CD25+FoxP3+ regulatory T cells (T(reg)) independent of antigen specificity. Type II monocyte-induced regulatory T cells specific for a foreign antigen ameliorated experimental autoimmune encephalomyelitis (EAE), indicating that neither GA specificity nor recognition of self-antigen was required for their therapeutic effect. Adoptive transfer of type II monocytes reversed EAE, suppressed T(H)17 cell development and promoted both T(H)2 differentiation and expansion of T(reg) cells in recipient mice. This demonstration of adoptive immunotherapy by type II monocytes identifies a central role for these cells in T cell immune modulation of autoimmunity.

IL-17 family cytokines and the expanding diversity of effector T cell lineages

Since its conception two decades ago, the Th1-Th2 paradigm has provided a framework for understanding T cell biology and the interplay of innate and adaptive immunity. Naive T cells differentiate into effector T cells with enhanced functional potential for orchestrating pathogen clearance largely under the guidance of cytokines produced by cells of the innate immune system that have been activated by recognition of those pathogens. This secondary education of post-thymic T cells provides a mechanism for appropriately matching adaptive immunity to frontline cues of the innate immune system. Owing in part to the rapid identification of novel cytokines of the IL-17 and IL-12 families using database searches, the factors that specify differentiation of a new effector T cell lineage-Th17-have now been identified, providing a new arm of adaptive immunity and presenting a unifying model that can explain many heretofore confusing aspects of immune regulation, immune pathogenesis, and host defense.

T(H)-17 cells in the circle of immunity and autoimmunity

CD4(+) effector T cells have been categorized into two subsets: T helper type 1 (T(H)1) and T(H)2. Another subset of T cells that produce interleukin 17 (IL-17; 'T(H)-17 cells') has been identified that is highly proinflammatory and induces severe autoimmunity. Whereas IL-23 serves to expand previously differentiated T(H)-17 cell populations, IL-6 and transforming growth factor-beta (TGF-beta) induce the differentiation of T(H)-17 cells from naive precursors. These data suggest a dichotomy between CD4(+) regulatory T cells positive for the transcription factor Foxp3 and T(H)-17 cells: TGF-beta induces Foxp3 and generates induced regulatory T cells, whereas IL-6 inhibits TGF-beta-driven Foxp3 expression and together with TGF-beta induces T(H)-17 cells. Emerging data regarding T(H)-17 cells suggest a very important function for this T cell subset in immunity and disease.

Elevated neuronal expression of CD200 protects Wlds mice from inflammation-mediated neurodegeneration

Axonal damage secondary to inflammation is likely the substrate of chronic disability in multiple sclerosis and is found in the animal model of experimental autoimmune encephalomyelitis (EAE). Wld(s) mice have a triplication of the fusion gene Ube4b/Nmnat and a phenotype of axon protection. Wld(s) mice develop an attenuated disease course of EAE, with decreased demyelination, reduced axonal pathology, and decreased central nervous system (CNS) macrophage and microglial accumulation. We show that attenuated disease in Wld(s) mice was associated with robust constitutive expression of the nonsignaling CD200 molecule on neurons in the CNS compared with control mice. CD200 interacts with its signaling receptor CD200R, which we found to be expressed on microglia, astrocytes, and oligodendrocytes at similar levels in control and Wld(s) mice. Administration of blocking anti-CD200 antibody to Wld(s) mice abrogated disease attenuation and was associated with increased CNS inflammation and neurodegeneration. In vitro, Wld(s) neuronal cultures were protected from microglial-induced neurotoxicity compared with control cultures, but protection was abrogated by anti-CD200 antibody. The CD200-CD200R pathway plays a critical role in attenuating EAE and reducing inflammation-mediated damage in the CNS. Strategies that up-regulate the expression of CD200 in the CNS or molecules that ligate the CD200R may be relevant as neuroprotective strategies in multiple sclerosis.

Role of Stat4-mediated signal transduction events in the generation of aggressor CD4+ T cells in herpetic stromal keratitis pathogenesis

Ocular infection with herpes simplex virus (HSV) causes a vision-impairing inflammatory reaction called herpetic stromal keratitis. In murine models, herpetic stromal keratitis lesions appear to be immunopathologic, mediated by CD4(+) T cells of Th1 phenotype. To provide insight about cytokine networks and signaling events involved in the development of aggressor CD4(+) T cells, ocular HSV infection was followed in mice deficient in Stat4 (Stat4(-/-) mice), the signal transducer for the cytokine interleukin-12 (IL-12). After ocular HSV infection of Stat4(-/-) and control BALB/c mice, clinical, histologic, and immunologic analyses were carried out. Further, to evaluate the involvement of Stat4 in the development of this aggressor population, naive CD4(+) T cells from Stat4(-/-) and BALB/c mice were adoptively transferred to C.B-17 SCID mice 1 day after corneal infection. Although Stat4(-/-) mice demonstrated increased susceptibility to lethal encephalitis and facial lesions, interestingly, these mice had less severe stromal keratitis in comparison to control animals. Adoptive transfer of naive CD4(+) T cells from Stat4(-/-) mice failed to produce disease in infected SCID recipients. The data imply a significant role of Stat4-mediated signaling events in the generation of an aggressor CD4(+) T cell population in stromal keratitis pathogenesis.

Targeting of the Transcription Factor STAT4 by Antisense Phosphorothioate Oligonucleotides Suppresses Collagen-Induced Arthritis

The transcription factor STAT4 mediates signals of various proinflammatory cytokines, such as IL-12, IL-15, and IL-23, that initiate and stabilize Th1 cytokine production. Although Th1 cytokine production has been suggested to play a major pathogenic role in rheumatoid arthritis, the role of STAT4 in this disease is poorly understood. In this study, we demonstrate a key functional role of STAT4 in murine collagen-induced arthritis (CIA). In initial studies we found that STAT4 expression is strongly induced in CD4(+) T cells and to a lesser extent in CD11b(+) APCs during CIA. To analyze the role of STAT4 for arthritis manifestation, we next investigated the outcome of interfering with STAT4 gene expression in CIA by using STAT4-deficient mice. Interestingly, STAT4-deficient mice developed significantly less severe arthritis than wild-type control mice and the T cells from such mice produced less IL-6, TNF, and IL-17. In addition, the targeting of STAT4 expression by a specific antisense phosphorothioate oligonucleotide directed at the translation start site suppressed STAT4 levels and signs of CIA even when applied during the onset of disease manifestation. These data suggest a key regulatory role of STAT4 in the pathogenesis and manifestation of murine collagen-induced arthritis. Furthermore, the targeting of STAT4 emerges as a novel approach to therapy for chronic arthritis.

CD5-CK2 binding/activation-deficient mice are resistant to experimental autoimmune encephalomyelitis: protection is associated with diminished populations of IL-17-expressing T cells in the central nervous system

Regulating the differentiation and persistence of encephalitogenic T cells is critical for the development of experimental autoimmune encephalomyelitis (EAE). We reported recently that CD5 has an engagement-dependent prosurvival activity in T cells that played a direct role in the induction and progression EAE. We predicted that CD5 regulates T cell apoptosis/survival through the activation of CK2, a prosurvival serine/threonine kinase that associates with the receptor. To test this hypothesis, we generated mice expressing CD5 with the inability to bind and activate CK2 and assessed their susceptibility to EAE. We found mice deficient in CD5-CK2 signaling pathway were mostly resistant to the development of EAE. Resistance to EAE was associated with a dramatic decrease in a population of effector infiltrating Th cells that coexpress IFN-gamma and IL-17 and, to a lesser extent, cells that express IFN-gamma or IL-17 in draining lymph nodes and spinal cords. We further show that T cells deficient in CD5-CK2 signaling hyperproliferate following primary stimulation; however, following restimulation, they rapidly develop nonresponsiveness and exhibit elevated activation-induced cell death. Our results provide a direct role for CD5-CK2 pathway in T cell activation and persistence of effector T cells in neuroinflammatory disease. This study predicts that targeting of IFN-gamma(+)/IL-17(+) infiltrating Th cells will be useful for the treatment of multiple sclerosis and other systemic autoimmune diseases.

The role of CD4 T cells in the pathogenesis of multiple sclerosis

T lymphocytes play a central role in the pathogenesis of multiple sclerosis (MS) (Zhang et al., 1992). Both CD4+ and CD8+ T cells have been demonstrated in MS lesions, with CD4+ T cells predominating in acute lesions and CD8+ T cells being observed more frequently in chronic lesions (Raine, 1994). Additionally, T cells are found in all four of the described histopathologic subtypes of MS (Lucchinetti et al., 2000). Activated myelin-reactive CD4+ T cells are present in the blood and cerebrospinal fluid (CSF) of MS patients; in contrast, only nonactivated myelin-reactive T cells are present in the blood of controls (Zhang et al., 1994). The success of several T-cell-targeted therapies in MS reinforces the importance of the role of the T cell in MS pathogenesis. Here, we outline basic concepts in CD4+ T-cell immunology and summarize the current understanding of the role of CD4+ T cells in the pathogenesis of MS.

Cardiac and Skin Xenograft Survival in Different Recipient Mouse Strains

BACKGROUND

There are conflicting reports on the importance of antibody and cell-mediated mechanisms and the influence of TH1 or TH2 cytokines on acute vascular xenograft rejection. We sought to resolve some of the recent discrepancies in the rat-to-mouse xenograft model where different recipient strains are used and investigated the TH1/TH2 influence on rejection.

METHODS

Lewis rat heart xenograft survival was compared between BALB/c and C57BL/6 recipients. Antigraft antibody deposition, serum anti-rat antibody levels and B-cell deficient recipients were used to examine the contribution of antibody to rejection. To further investigate a TH1 or TH2 bias effect in vivo, we used BALB/c STAT4 knockout (KO) and STAT6 KO recipient mice. Experiments were repeated with rat skin xenografts to examine TH1/TH2 influences on cell-mediated rejection.

RESULTS

The median survival (MS) of rat heart xenografts in BALB/c and C57BL/6 mice was five and eight days, respectively (P = 0.002). The MS in B-cell deficient mice was 16 days (P < 0.001). The MS in STAT4 KO and STAT6 KO mice was six and seven days respectively (P = 0.009). All non-B-cell deficient recipients showed strong IgM deposition and histological features of both cellular and antibody-mediated rejection. There was no correlation between serum anti-rat antibody levels and graft outcome or graft deposition. There was no survival difference of skin xenografts in BALB/c, C57BL/6, B-cell deficient, STAT6 KO, or STAT4 KO mice (8-9 days).

CONCLUSIONS

Both humoral and cell-mediated immunity have significant roles in vascularized heart xenograft rejection. TH1/TH2 biases minimally affect rejection through humoral but not cellular immunity.

Impairment of axotomy-induced pituitary adenylyl cyclase-activating peptide gene expression in T helper 2 lymphocyte-deficient mice

CD4+ (T helper) lymphocytes appear to play important roles in neuron survival and regeneration after injury, although their functions in regulating gene expression in injured neurons are unknown. Mice with targeted mutations in the STAT4 and STAT6 genes are deficient in T helper (Th)1 and Th2 responses, respectively, and have been used to determine the relative importance of T helper subsets in a variety of inflammatory processes. As pituitary adenylyl cyclase-activating peptide mRNA is normally strongly induced in facial motor neurons after axotomy, we examined this induction in Th1 and Th2 lymphocyte-deficient and control Balb/C wild-type mice. As previously reported, pituitary adenylyl cyclase-activating peptide gene expression was strongly induced in ipsilateral but not contralateral motor neurons in the facial motor nucleus of wild-type mice. The mean number of hybridizing motor neurons in STAT4-deficient mice did not differ from that in wild-type mice, whereas the number in STAT6 mice was reduced by more than 50%. The results indicate that STAT6 plays a key role in the upregulation of pituitary adenylyl cyclase-activating peptide gene expression in facial motor neurons after injury, possibly through its role in regulating T helper cell differentiation to the type 2 phenotype.

Expanding the effector CD4 T-cell repertoire: the Th17 lineage

The Th1/Th2 paradigm has provided the framework for understanding CD4 T-cell biology and the interplay between innate and adaptive immunity for almost two decades. Recent studies have defined a previously unknown arm of the CD4 T-cell effector response--the Th17 lineage--that promises to change our understanding of immune regulation, immune pathogenesis and host defense. The factors that specify differentiation of IL-17-producing effector T-cells from naïve T-cell precursors are being rapidly discovered and are providing insights into mechanisms by which signals from cells of the innate immune system guide alternative pathways of Th1, Th2 or Th17 development.

Mycobacterium tuberculosis in the adjuvant modulates the balance of Th immune response to self-antigen of the CNS without influencing a “core” repertoire of specific T cells

In the present study, we use modified CDR3 beta-chain spectratyping (immunoscope) to dissect the effect of Mycobacterium tuberculosis (MT)-derived proteins on individual PLP139-151-specific cells in the SJL mouse strain. In this model, the immunoscope technique allows the characterization of a public TCR that involves rearrangement of Vbeta10 and Jbeta1.1 and a semi-private TCR characterized by rearrangement of Vbeta4 and Jbeta1.6. Both rearrangements are specific for PLP139-151 and sequences of the CDR3 region of the two beta-chains show a conserved motif for the public rearrangement and related but more variable sequences for the semi-private rearrangement. MT-derived proteins promote increase of IFN-gamma-secreting cells. However, we observe that the presence and amount of MT used during immunization have no effect on the frequency of usage, polarization and in vivo expansion of cells carrying the studied rearrangements. Rather, the strong Th1-promoting effect of adjuvant is possibly due to recruitment toward Th1 of a wider spectrum of TCR repertoires. Therefore, instead of having a comprehensive effect on the entire repertoire, MT modulates the immune response by affecting a subset of antigen-specific T cells whose polarization can be adapted to the environment. This step establishes the final balance between Th1 and Th2 and may be essential for the enhancement or protection of disease.

Differential requirement of signal transducer and activator of transcription-4 (Stat4) and Stat6 in a thyrotropin receptor-289-adenovirus-induced model of Graves' hyperthyroidism

T helper type 1 (Th1) and Th2 cells have critical roles in the development of cell-mediated and humoral immune responses, respectively. This division of function predicts that Th1 cells mediate inflammatory diseases and Th2 cells promote antibody (Ab)-mediated autoimmunity. Our previous studies using HEK-293 cells expressing the extracellular domain of the TSH receptor (TSHR) showed that Stat4-/- mice, which lack Th1 cells, are susceptible, whereas Stat6-/- mice, which lack Th2 cells, are resistant to the induction of Graves' hyperthyroidism. To investigate the role of Stat4 and Stat6 genes in other murine models of hyperthyroidism, we injected wild-type BALB/c, Stat4-/-, and Stat6-/- mice with an adenovirus expressing amino acid residues 1-289 of TSHR (TSHR-289-ad or 289-ad). The viral system induces a much stronger immune response with much more rapid onset of disease. Our results showed that 56% of wild-type, 75% of Stat4-/-, and 39% of Stat6-/- mice developed hyperthyroidism. Hyperthyroid mice exhibited thyroid stimulatory Abs. The Stat4-/- mice developed a higher incidence and greater severity of hyperthyroidism compared with wild-type and Stat6-/- mice. BALB/c and Stat4-/- mice showed significantly higher TSHR Abs of the IgG1 subclass and IL-4 compared with Stat6-/- mice. In contrast, Stat6-/- mice had predominantly the IgG2a subclass of TSHR Ab and produced significantly higher amounts of IFN-gamma than BALB/c and Stat4-/- mice. All hyperthyroid mice showed enlarged thyroid glands with hyperactivity. These results suggest that in the TSHR-289-ad model, the Th2 cells are more efficient in mediating disease, but in the absence of Th2 cells, Th1 cells may still initiate a reduced incidence of Graves' hyperthyroidism.

STAT4- and STAT6-signaling molecules in a murine model of multiple sclerosis

Epidemiological studies suggest that an environmental factor (possibly a virus) acquired early in life may trigger multiple sclerosis (MS). The virus may remain dormant in the central nervous system but then becomes activated in adulthood. All existing models of MS are characterized by inflammation or demyelination that follows days after virus infection or antigen inoculation. While investigating the role of CD4+ T cell responses following Theiler's virus infection in mice deficient in STAT4 or STAT6, we discovered a model in which virus infection was followed by demyelination after a very prolonged incubation period. STAT4-/- mice were resistant to demyelination for 180 days after infection, but developed severe demyelination after this time point. Inflammatory cells and up-regulation of Class I and Class II MHC antigens characterized these lesions. Virus antigen was partially controlled during the early chronic phase of the infection even though viral RNA levels remained high throughout infection. Demyelination correlated with the appearance of virus antigen expression. Bone marrow reconstitution experiments indicated that the mechanism of the late onset demyelination was the result of the STAT4-/- immune system. Thus, virus infection of STAT4-/- mice results in a model that may allow for dissection of the immune events predisposing to late-onset demyelination in MS.

Understanding the IL-23-IL-17 immune pathway

Interleukin (IL)-23 is a heterodimeric cytokine closely related to IL-12. Yet, despite a strong structural relationship that includes a shared p40 subunit, this does not translate into functional similarity. In fact, the opposite is true, in that these two cytokines appear to have profoundly different roles in regulating host immune responses. It is now clear that IL-23 has key roles in autoimmune destruction in experimental allergic encephalomyelitis, collagen-induced arthritis and inflammatory bowel disease. IL-23 drives the development of autoreactive IL-17-producing T cells and promotes chronic inflammation dominated by IL-17, IL-6, IL-8 and tumor necrosis factor as well as neutrophils and monocytes. It is unlikely that IL-23 and its downstream effects evolved just to cause autoimmunity, but its real benefit to the host and the lineage relationship between IL-17-producing cells and T helper 1 cells remain unclear. By comparing the pathophysiological function of IL-12 and IL-23 in the context of host defense and autoimmune inflammation, we are beginning to understand the novel IL-23-IL-17 immune pathway.

Interleukin 17-producing CD4+ effector T cells develop via a lineage distinct from the T helper type 1 and 2 lineages

CD4(+) T cells producing interleukin 17 (IL-17) are associated with autoimmunity, although the precise mechanisms that control their development are undefined. Here we present data that challenge the idea of a shared developmental pathway with T helper type 1 (T(H)1) or T(H)2 lineages and instead favor the idea of a distinct effector lineage we call 'T(H)-17'. The development of T(H)-17 cells from naive precursor cells was potently inhibited by interferon-gamma (IFN-gamma) and IL-4, whereas committed T(H)-17 cells were resistant to suppression by T(H)1 or T(H)2 cytokines. In the absence of IFN-gamma and IL-4, IL-23 induced naive precursor cells to differentiate into T(H)-17 cells independently of the transcription factors STAT1, T-bet, STAT4 and STAT6. These findings provide a basis for understanding how inhibition of IFN-gamma signaling enhances development of pathogenic T(H)-17 effector cells that can exacerbate autoimmunity.

Stat4-null non-obese diabetic mice: protection from diabetes and experimental allergic encephalomyelitis, but with concomitant epitope spread

There is much interest in therapeutic manipulation of cytokine responses in autoimmunity, yet studies in mouse models have sometimes produced conflicting findings as to the role of particular mediators in disease. Examples include the contradictory findings regarding susceptibility to experimental allergic encephalomyelitis (EAE) or diabetes in knockout mice for various individual Th1 or Th2 cytokines or their receptors. An alternative approach to the analysis of Th1 and Th2 mechanisms in these diseases is to investigate strains carrying a null mutation for molecules involved in cytokine receptor signal transduction, signal transducer and activator of transcription (Stat4) and Stat6. Stat4 is pivotal in Th1 polarization, being activated when IL-12 binds the IL-12R and leading to the production of IFNgamma. We here report disease susceptibility in non-obese diabetic mice carrying a Stat4-null mutation. Knockout mice were almost completely protected from diabetes, only rarely showing pancreatic peri-islet infiltrates. Furthermore, there was near complete protection from the induction of EAE by either of the two encephalitogenic myelin epitopes. Despite this protection, Stat4-null mice showed clear epitope spread compared with controls during myelin oligodendrocyte glycoprotein-induced EAE as judged by T cell proliferation, although this was not associated with a strong Th1 response to the initial or spread epitope and, furthermore, there was no evidence of a switch to Th2 cytokines.

5-aminoimidazole-4-carboxamide ribonucleoside: a novel immunomodulator with therapeutic efficacy in experimental autoimmune encephalomyelitis

Experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis, is a Th1-mediated inflammatory demyelinating disease of the CNS. AMP-activated protein kinase was reported recently to have anti-inflammatory activities by negatively regulating NF-kappaB signaling. In this study, we investigated the prophylactic and therapeutic efficacy of an AMP-activated protein kinase activator, 5-aminoimidazole-4-carboxamide ribonucleoside (AICAR), in active and passive EAE induced by active immunization with PLP(139-151) or MOG(35-55) and in adoptive transfer of PLP(139-151)-sensitized T cells, respectively. In vivo treatment with AICAR exerted both prophylactic and therapeutic effects on EAE, attenuating the severity of clinical disease. The anti-inflammatory effects of AICAR were associated with the inhibition of the Ag-specific recall responses and inhibition of the Th1-type cytokines IFN-gamma and TNF-alpha, whereas it induced the production of Th2 cytokines IL-4 and IL-10. Treatment of PLP(139-151)-specific T cells in vitro with AICAR decreased their expression of T-bet in response to IL-12, a Th1 transcription factor, whereas in response to IL-4, it induced the expression and phosphorylation of Th2 transcription factors GATA3 and STAT6, respectively. Moreover, treatment of APCs in vitro with AICAR inhibited their capability to present the proteolipid protein peptide to PLP(139-151)-specific T cells. In an irrelevant Th1-mediated, OT-2 TCR transgenic mouse model, AICAR impaired in vivo Ag-specific expansion of CD4(+) T cells. Together, these findings show for the first time that AICAR is a novel immunomodulator with promising beneficial effects for the treatment of multiple sclerosis and other Th1-mediated inflammatory diseases.

Signaling by IL-12 and IL-23 and the immunoregulatory roles of STAT4

Produced in response to a variety of pathogenic organisms, interleukin (IL)-12 and IL-23 are key immunoregulatory cytokines that coordinate innate and adaptive immune responses. These dimeric cytokines share a subunit, designated p40, and bind to a common receptor chain, IL-12R beta 1. The receptor for IL-12 is composed of IL-12R beta 1 and IL-12R beta 2, whereas IL-23 binds to a receptor composed of IL-12R beta 1 and IL-23R. Both cytokines activate the Janus kinases Tyk2 and Jak2, the transcription factor signal transducer and activator of transcription 4 (STAT4), as well as other STATs. A major action of IL-12 is to promote the differentiation of naive CD4+ T cells into T-helper (Th) 1 cells, which produce interferon (IFN)-gamma, and deficiency of IL-12, IL-12R subunits or STAT4 is similar in many respects. In contrast, IL-23 promotes end-stage inflammation. Targeting IL-12, IL-23, and their downstream signaling elements would therefore be logical strategies for the treatment of immune-mediated diseases.

STATs as critical mediators of signal transduction and transcription: lessons learned from STAT5

Signal transducers and activators of transcription (Stats) comprise a family of seven transcription factors that are activated by a variety of cytokines, hormones and growth factors. Stats are activated through tyrosine phosphorylation, mainly by Jak kinases, that lead to their dimerization, nuclear translocation and regulation of target gene expression. Stat5 was originally identified as a transcription factor that regulates the beta-casein gene in response to prolactin (PRL), but Stat5 is activated also by several other cytokines and growth factors. The molecular mechanisms that underlie Stat5-mediated transcription involve interactions and cooperation with sequence specific transcription factors and transcriptional coregulators. Our studies identified p100 protein as a coactivator for Stat5, and suggest the existence of a positive regulatory loop in PRL-induced transcription, where PRL stabilizes p100 protein, which in turn can cooperate with Stat5 in transcriptional activation. Suppressors of cytokine signaling (SOCS) proteins are important negative regulators of Stats. A target gene for Stat5, the serine/threonine kinase Pim-1, was found to cooperate with SOCS-1 and SOCS-3 to inhibit Stat5 activity suggesting that Pim-1 together with SOCS-1 and SOCS-3 are components of a negative feedback mechanism that allows Stat5 to regulate its own activation.

Effect of targeted disruption of signal transducer and activator of transcription (Stat)4 and Stat6 genes on the autoimmune diabetes development induced by multiple low doses of streptozotocin

The MLDS (multiple low doses of streptozotocin) model of diabetes was induced in Stat4(-/-), Stat6(-/-), and double-deficient Stat4(-/-)/6(-/-) mice to examine the role of STAT4/STAT6 deficiency in development of autoimmune diabetes. Cytokine production of T-cells from Stat4(-/-) mice confirmed a predominantly Th2-type immune response. Stat4(-/-) mice exhibited delayed onset and reduced severity of disease compared to wild-type (WT) mice. In contrast, STAT6 deficiency, with a predominant Th1 response, did not influence the kinetics or severity of MLDS-induced autoimmune diabetes. Interestingly, Stat4(-/-)/6(-/-) mice, with a prominent Th1-type response, experienced an accelerated and aggravated course of diabetes after MLDS, implicating a STAT4-independent Th1 response in the immunopathogenesis of MLDS-induced autoimmune diabetes. The sensitivity of islet cells from Stat4(-/-) or Stat4(-/-)/6(-/-) mice to cytokines and STZ was not different from that of islet cells of WT mice. Hence, the observed effects of STAT4 and STAT4/6 deficiency on MLDS-induced autoimmune diabetes are likely due to their effects on T-cell responses.

Silencing T-bet defines a critical role in the differentiation of autoreactive T lymphocytes

As a means of developing therapies that target the pathogenic T cells in multiple sclerosis (MS) without compromising the immune system or eliciting systemic side effects, we investigated the use of T-bet-specific antisense oligonucleotides and small interfering RNAs (siRNA) to silence T-bet expression in autoreactive encephalitogenic T cells and evaluated the biological consequences of this suppression in experimental autoimmune encephalomyelitis, a model for MS. The T-bet-specific AS oligonucleotide and siRNA suppressed T-bet expression, IFNgamma production, and STAT1 levels during antigen-specific T cell differentiation. In vitro suppression of T-bet during differentiation of myelin-specific T cells and in vivo administration of a T-bet-specific antisense oligonucleotide or siRNA inhibited disease. T-bet was shown to bind the IFNgamma and STAT1 promoters, but did not regulate the IL-12/STAT4 pathway. Since T-bet regulates IFNgamma production in CD4(+) T cells, but to a lesser extent in most other IFNgamma-producing cells, T-bet may be a target for therapeutics for Th1-mediated diseases.

Schistosoma mansoni infection modulates the immune response against allergic and auto-immune diseases

Chronic Schistosoma mansoni infection leads to a type 2-immune response with increased production of interleukin (IL-10). Evidence indicates chronic exposure to S. mansoni down regulates the type 1 immune response and prevents the onset of Th1-mediated diseases such as multiple sclerosis, diabetes mellitus and Crohn's disease. Furthermore, our own studies have revealed that chronic exposure to S. mansoni also down regulates atopic disease, Th2-mediated diseases. Our studies show an inverse association between the skin prick test reactivity and infection with S. mansoni and show the severity of asthma is reduced in subjects living in an endemic area of S. mansoni. Moreover, we hypothesize the mechanisms involved in the modulation of inflammatory response in atopic individuals, is likely dependent on IL-10 production, an anti-inflammatory cytokine elevated during helminth infections. Patients with asthma and helminth infections produced less IL-5 than patients with asthma without helminth infections, and this down regulation could, in part, be mediated by IL-10. In conclusion, helminthic infections, through induction of regulatory mechanisms, such as IL-10 production, are able to modulate the inflammatory immune response involved in the pathology of auto-immune and allergic disease.

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Interferon α but Not Interleukin 12 Activates STAT4 Signaling in Human Vascular Endothelial Cells

STAT4 signaling, activated by either interleukin 12 (IL12) or interferon alpha (IFNalpha), promotes T(H)1 responses in CD4(+) T cells. Vascular endothelial cells (EC) may also become polarized in response to various cytokines, favoring recruitment and activation of T(H)1 or T(H)2 effector cells. Here we have investigated the role of the STAT4 pathway in EC. Cultured human umbilical vein EC (HUVEC) express low levels of STAT4, which may be tyrosine-phosphorylated by treatment with IFNalpha but not IL12. This is because HUVEC lack both subunits of the IL12 receptor (IL12Rbeta1 and IL12Rbeta2), even following treatment with various cytokines. IL12 phosphorylation of STAT4 can be observed in HUVEC that have been transduced to express the IL12R. To identify STAT4-induced genes we pursued three approaches: analysis by DNA microarray and quantitative RT-PCR (Q-PCR) of the IL12 responses in IL12R-transduced EC; analysis by Q-PCR of IFNalpha responses in STAT4-overexpressing EC; and analysis of IFNalpha responses in U3A neuroblastoma cell lines that express either STAT1 or STAT4, but not both. In all three instances we observe STAT4-mediated induction of the chemokine monocyte chemoattractant protein 1 (MCP1) and suppressor of cytokine signaling 3 (SOCS3) mRNA, and we confirm the production of each protein in both IL12R-transduced EC and STAT4-transduced U3A cells. These observations reveal that there is a STAT4 response of EC, activated by IFNalpha but not IL12, and that it may modulate the pro-inflammatory behavior of EC.

Increased numbers of committed myeloid progenitors but not primitive hematopoietic stem/progenitors in mice lacking STAT6 expression

Signal transducer and activator of transcription-6 (STAT6) plays important roles in cytokine signaling via interleukin-4 and -13 receptors (IL-4R and IL-13R). Mice in which STAT6 has been disrupted by homologous recombination show defects in T helper cell type 2 (Th2) lymphocyte production, resulting in an accumulation of Th1 cells. In addition to defects in differentiation and proliferation of T lymphocytes, STAT6-deficient mice show increased cell-cycle activation and frequency of myeloid progenitors. Although this has been shown to be mediated through Oncostatin M production by T cells, IL-4Ralpha and STAT6 have also recently been found to be enriched for expression in primitive hematopoietic stem cells (HSCs) in gene expression-profiling studies. Therefore, we have investigated whether defects in hematopoietic function in mice lacking STAT6 expression extended into the primitive hematopoietic compartments of the bone marrow. Here, we report that STAT6 deficiency increased bone marrow-committed myeloid progenitors but did not alter the number of cells enriched for HSC/multipotent progenitors, primitive cobblestone area-forming cells assayed in vitro, or bone marrow short-term or long-term repopulating cells assayed in vivo. Therefore, the requirement for STAT6 activation during hematopoiesis is limited, and primitive hematopoietic cell types are insulated against possible effects of cytokine stimulation by Th1 cells.

Defining Th1 and Th2 Immune Responses in a Reciprocal Cytokine Environment In Vivo

The ability of committed Th1 and Th2 cells to function in altered cytokine environments is a central issue in autoimmune and immune-mediated diseases. Therefore, it is of interest to study the ability of Th1 or Th2 cells to expand and produce cytokine reciprocal environments in vivo. Using STAT4- and STAT6-deficient mice, we studied the expansion and cytokine production of Ag-specific Th1 or Th2 cells after transfer into Th1, Th2, or wild-type recipients. Our data show that these Th1 or Th2 cells proliferated and clonally expanded normally, regardless of the in vivo cytokine environment. These data have implications for the treatment of immune-mediated diseases by immunomodulatory agents that alter the cytokine milieu in vivo.

Potential Targets of 3-Hydroxy-3-Methylglutaryl Coenzyme A Reductase Inhibitor for Multiple Sclerosis Therapy

The 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors or statins are newly identified immunomodulators. In vivo treatment of SJL/J mice with lovastatin reduced the duration and clinical severity of active and passive experimental autoimmune encephalomyelitis (EAE), an animal model for multiple sclerosis. Lovastatin induced the expression of GATA3 and the phosphorylation of STAT6, whereas it inhibited tyrosine phosphorylation of Janus kinase 2, tyrosine kinase 2, and STAT4. Inhibition of the Janus kinase-STAT4 pathway by lovastatin modulated T0 to Th1 differentiation and reduced cytokine (IFN-gamma and TNF-alpha) production, thus inducing Th2 cytokines (IL-4, IL-5, and IL-10). It inhibited T-bet (T box transcription factor) and NF-kappaB in activated T cells and significantly reduced infiltration of CD4- and MHC class II-positive cells to CNS. Further, it stabilized IL-4 production and GATA-3 expression in differentiated Th2 cells, whereas in differentiated Th1 cells it inhibited the expression of T-bet and reduced the production of IFN-gamma. Moreover, lovastatin-exposed macrophage and BV2 (microglia) in allogeneic MLRs induced the production of the anti-inflammatory cytokine IL-10. These observations indicate that the anti-inflammatory effects of lovastatin are mediated via T cells as well as APCs, because it modulates the polarization patterns of naive T cell activation in an APC-independent system. Together, these findings reveal that lovastatin may have possible therapeutic value involving new targets (in both APCs and T cells) for the treatment of multiple sclerosis and other inflammatory diseases.

The Susceptibility to Experimental Myasthenia Gravis of STAT6−/− and STAT4−/− BALB/c Mice Suggests a Pathogenic Role of Th1 Cells

Autoantibodies to the muscle acetylcholine receptor (AChR) cause the symptoms of human and experimental myasthenia gravis (EMG). AChR-specific CD4+ T cells permit development of these diseases, but the role(s) of the Th1 and Th2 subsets is unclear. The STAT4 and STAT6 proteins, which mediate intracellular cytokine signaling, are important for differentiation of Th1 and Th2 cells, respectively. Wild-type (WT) BALB/c mice, which are prone to develop Th2 rather than Th1 responses to Ag, are resistant to EMG. We have examined the role of Th1 and Th2 cells in EMG using STAT4 (STAT4-/-)- or STAT6 (STAT6-/-)-deficient BALB/c mice. After AChR immunization, STAT6-/- mice were susceptible to EMG: they developed more serum anti-AChR Ab, and had more complement-fixing anti-AChR IgG2a and 2b and less IgG1 than WT or STAT4-/- mice. The susceptibility to EMG of STAT6-/- mice is most likely related to the Th1 cell-induced synthesis of anti-AChR Ab, which trigger complement-mediated destruction of the neuromuscular junction. CD4+ T cells of the STAT6-/- mice had proliferative responses to the AChR comparable to those of WT and STAT4-/- mice, and recognized similar AChR epitopes. STAT6-/- mice had abundant AChR-specific Th1 cells, which were nearly absent in WT and STAT4-/- mice. Spleen and lymph nodes from STAT6-/- mice contained cells that secreted IL-4 when cultured with AChR: these are most likely STAT6-independent cells, stimulated in a non-Ag-specific manner by the cytokines secreted by AChR-specific Th1 cells.

Role of costimulatory pathways in the pathogenesis of multiple sclerosis and experimental autoimmune encephalomyelitis

Multiple sclerosis is an immune-mediated disorder of the central nervous system. T lymphocytes are thought to play a central role in the initiation and potentially in the propagation of this disease. Two signals are required for T-cell activation. The first signal consists of the interaction of the T-cell receptor with antigen presented by the MHC molecule on antigen-presenting cells. The second signal requires engagement of costimulatory receptors on T cells with their ligands on antigen-presenting cells. Several costimulatory pathways have been shown to play an important role in T-lymphocyte activation. Here we will review the current literature on the contribution of the B7-1/2-CD28/CTLA-4, inducible costimulatory molecule-B7h, programmed death pathway 1-programmed death pathway ligand 1/ligand 2, CD40-CD154, OX40-OX40 ligand, and CD137-CD137 ligand pathways to the pathogenesis of multiple sclerosis and their potential roles as therapeutic targets.

Regulatory functions of CD8+CD28- T cells in an autoimmune disease model

CD8+ T cell depletion renders CD28-deficient mice susceptible to experimental autoimmune encephalomyelitis (EAE). In addition, CD8-/-CD28-/- double-knockout mice are susceptible to EAE. These findings suggest a role for CD8+ T cells in the resistance of CD28-deficient mice to disease. Adoptive transfer of CD8+CD28- T cells into CD8-/- mice results in significant suppression of disease, while CD8+CD28+ T cells demonstrate no similar effect on the clinical course of EAE in the same recipients. In vitro, CD8+CD28- but not CD8+CD28+ T cells suppress IFN-gamma production of myelin oligodendrocyte glycoprotein-specific CD4+ T cells. This suppression requires cell-to-cell contact and is dependent on the presence of APCs. APCs cocultured with CD8+CD28- T cells become less efficient in inducing a T cell-dependent immune response. Such interaction prevents upregulation of costimulatory molecules by APCs, hence decreasing the delivery of these signals to CD4+ T cells. These are the first data establishing that regulatory CD8+CD28- T cells occur in normal mice and play a critical role in disease resistance in CD28-/- animals.

Signaling molecules as therapeutic targets in allergic diseases

A molecular understanding of physiologic and pathologic processes requires complete knowledge about the signal transduction mechanism of involved cells. Signal transduction research is a rapidly growing field in basic science. Unlike intercellular inflammatory mediators, signaling molecules show less functional redundancy. This allows inhibition of multiple cytokines/mediators by blocking one common signaling molecule. Interference with signaling pathways has shown significant potential for inhibition of fundamental processes as well as clinical phenotype of allergic diseases. The purpose of this review was to provide a theoretical classification of signaling molecules based on their function and to analyze various strategies for developing effective signaling inhibitors for allergic diseases.

Critical role of the programmed death-1 (PD-1) pathway in regulation of experimental autoimmune encephalomyelitis

Experimental autoimmune encephalomyelitis (EAE) is mediated by autoantigen-specific T cells dependent on critical costimulatory signals for their full activation and regulation. We report that the programmed death-1 (PD-1) costimulatory pathway plays a critical role in regulating peripheral tolerance in murine EAE and appears to be a major contributor to the resistance of disease induction in CD28-deficient mice. After immunization with myelin oligodendrocyte glycoprotein (MOG) there was a progressive increase in expression of PD-1 and its ligand PD-L1 but not PD-L2 within the central nervous system (CNS) of mice with EAE, peaking after 3 wk. In both wild-type (WT) and CD28-deficient mice, PD-1 blockade resulted in accelerated and more severe disease with increased CNS lymphocyte infiltration. Worsening of disease after PD-1 blockade was associated with a heightened autoimmune response to MOG, manifested by increased frequency of interferon gamma-producing T cells, increased delayed-type hypersensitivity responses, and higher serum levels of anti-MOG antibody. In vivo blockade of PD-1 resulted in increased antigen-specific T cell expansion, activation, and cytokine production. Interestingly, PD-L2 but not PD-L1 blockade in WT animals also resulted in disease augmentation. Our data are the first demonstration that the PD-1 pathway plays a critical role in regulating EAE.

20. Immunologic neuromuscular disorders

Immune-mediated disorders of each of the structural subdivisions of the nervous and neuromuscular system have been described. Despite the immune privilege of the central nervous system, and to a lesser extent the peripheral nervous system, immune dysregulation is not uncommon. Environmental, genetic, and immunologic factors have been postulated to be involved in the development of these disorders. Major immune-mediated neurologic diseases of the central nervous system include multiple sclerosis and acute disseminated encephalomyelitis. Immune-mediated diseases of the peripheral nervous system include myasthenia gravis, Guillain-Barré syndrome, chronic inflammatory demyelinating polyneuropathy, idiopathic polymyositis, dermatomyositis, and inclusion body myositis. Some of these disorders, such as myasthenia gravis and certain forms of acute inflammatory demyelinating polyneuropathy, are clearly autoimmune in nature, whereas the immune system plays an important role in pathogenesis in others. Understanding the immune mechanisms of disease and uncovering potential therapeutic targets are essential for the design of new treatments. The epidemiology, pathogenesis, diagnostic criteria, and current therapeutic approaches to the major neuroimmunologic diseases are reviewed.

Stat4 and Stat6 signaling in hepatic ischemia/reperfusion injury in mice: HO-1 dependence of Stat4 disruption-mediated cytoprotection

Ischemia/reperfusion (I/R) injury remains an important problem in clinical organ transplantation. There is growing evidence that T lymphocytes, and activated CD4+ T cells in particular, play a key role in hepatic I/R injury. This study analyzes the role of signal transducer and activator of transcription 4 (Stat4) and Stat6 signaling in liver I/R injury. Using a partial lobar warm ischemia model, groups of wild-type (WT), T cell-deficient, Stat4-/Stat6-deficient knockout (KO) mice were assessed for the extent/severity of I/R injury. Ninety minutes of warm ischemia followed by 6 hours of reperfusion induced a fulminant liver failure in WT and Stat6 KO mice, as assessed by hepatocellular damage (serum alanine aminotransferase [sALT] levels), neutrophil accumulation (myeloperoxidase [MPO] activity) and histology (Suzuki scores). In contrast, T cell deficiency (nu/nu mice) or disruption of Stat4 signaling (Stat4 KO mice) reduced I/R insult. Unlike adoptive transfer of WT or Stat6-deficient T cells, infusion of Stat4-deficient T cells failed to restore hepatic I/R injury and prevented tumor necrosis factor alpha (TNF-alpha) production in nu/nu mice. Diminished TNF-alpha/Th1-type cytokine messenger RNA (mRNA)/protein elaborations patterns, along with overexpression of heme oxygenase-1 (HO-1)-accompanied hepatic cytoprotection in Stat4 KO recipients. In contrast, HO-1 depression restored hepatic injury in otherwise I/R resistant Stat4 KOs. In conclusion, Stat4 signaling is required for, whereas Stat4 disruption protects against, warm hepatic I/R injury in mice. The cytoprotection rendered by Stat4 disruption remains HO-1-dependent.

Multiple sclerosis: Cytokine receptors on oligodendrocytes predict innate regulation

Multiple sclerosis (MS) is an immune-mediated demyelinating condition in which numerous soluble mediators have been implicated. We have extended the repertoire of cytokines studied in MS tissue by examining interleukin (IL-4), IL-6, IL-10, IL-12, IL-18, interferon (IFNgamma), and their receptors and have compared patterns with those seen in normal subjects and other neurological diseases (OND). Expression was evaluated by immunocytochemistry and Western blots. Remarkably, oligodendrocytes expressed all the cytokine receptors examined, particularly Th2-type, constitutively in normal subjects and upregulated in disease. Microglial cells also expressed cytokine receptors at similar levels. Cytokine expression was invariably a feature of microglial cells, except for IL-10, which was exclusively astrocytic. Oligodendrocytes did not display cytokines, except for low levels of IL-18. Although no pattern was specific for MS, most molecules were upregulated in MS and OND. Downstream JAK/STAT molecules were correspondingly upregulated. Cytokine receptors on oligodendrocytes (and microglia), and their corresponding ligands on microglia (and astrocytes), may implicate paracrine/autocrine regulation and may bespeak innate immunity in the central nervous system.

A genomic view of helper T cell subsets

Genomic-scale gene expression profiling in combination with the availability of a draft sequence of the human genome is beginning to revolutionize the way immunology is done. The possibility of measuring levels of gene expression for tens of thousands of genes simultaneously and in a quantitative fashion aids in the definition of a comprehensive molecular phenotype of cells and cellular processes of the immune system in health and disease. T helper lymphocytes are an essential element of appropriate immune responses to pathogens. To achieve effective immunity, T helper cells differentiate into at least two specialized subsets that direct type 1 and type 2 immune responses. Here, I discuss recent progress that has been made in our understanding of the genetic program that controls the development and functional properties of helper T cell subsets.

Neonatal tolerance in the absence of Stat4- and Stat6- dependent Th cell differentiation

Neonatal tolerance to specific Ag is achieved by nonimmunogenic exposure within the first day of life. The mechanism that regulates this tolerance may provide the basis for successful organ transplantation and has recently been thought to be immune deviation from the inflammatory Th1 response to a Th2 response. To test the importance of Th2 cells in the establishment of neonatal tolerance, we examined neonatal tolerance in Stat4- and Stat6-deficient mice, which have reduced Th1 and Th2 cell development, respectively. Neonatal tolerance of both the T and B cell compartments in Stat4- and Stat6-deficient mice was similar to that observed in wild-type mice. Cytokine production shifted from a Th1 to a Th2 response in wild-type mice tolerized as neonates. In contrast, tolerance was observed in Stat6-deficient mice despite maintenance of a Th1 cytokine profile. These results suggest that cells distinct from Stat6-dependent Th2 cells are required for the establishment of neonatal tolerance.

Physiological Mechanisms of Regulating Alloimmunity: Cytokines, CTLA-4, CD25+ Cells, and the Alloreactive T Cell Clone Size

The mechanisms underlying physiological regulation of alloimmune responses remain poorly defined. We investigated the roles of cytokines, CTLA-4, CD25(+) T cells, and apoptosis in regulating alloimmune responses in vivo. Two murine cardiac transplant models were used, B10.D2 (minor mismatch) and C57BL/6 (major mismatch), into BALB/c recipients. Recipients were wild type, STAT4(-/-) (Th1 deficient), or STAT6(-/-) (Th2 deficient) mice. Minor mismatched allografts were accepted spontaneously in approximately 70% of wild type and STAT4(-/-) mice. By contrast, there was significantly shorter graft survival in minor mismatched STAT6(-/-) mice. Either the adoptive transfer of STAT4(-/-) splenocytes or the administration of IL-4Fc fusion protein into STAT6(-/-) mice resulted in long term graft survival. Blocking CTLA-4 signaling accelerated the rejection in all recipients, but was more pronounced in the minor combination. This was accompanied by an increased frequency of alloreactive T cells. Furthermore, CTLA-4 blockade regulated CD4(+) or CD8(+) as well as Th1 or Th2 alloreactive T cells. Finally, while anti-CD25 treatment prolonged graft survival in the major mismatched combination, the same treatment accelerated graft rejection in the minor mismatched group. The latter was associated with an increased frequency of alloreactive T cells and inhibition of T cell apoptosis. These data demonstrate that cytokine regulation, CTLA-4 negative signaling, and T cell apoptosis play critical roles in regulating alloimmunity, especially under conditions where the alloreactive T cell clone size is relatively small.