Interleukin 27 limits autoimmune encephalomyelitis by suppressing the development of interleukin 17-producing T cells

STAT3 is indispensable to IL-27-mediated cell proliferation but not to IL-27-induced Th1 differentiation and suppression of proinflammatory cytokine production

IL-27, a member of the IL-6/IL-12 family, activates both STAT1 and STAT3 through its receptor, which consists of WSX-1 and gp130 subunits, resulting in augmentation of Th1 differentiation and suppression of proinflammatory cytokine production. In the present study, we investigated the role of STAT3 in the IL-27-mediated immune functions. IL-27 induced phosphorylation of STAT1, -2, -3 and -5 in wild-type naive CD4+ T cells, but failed to induce that of STAT3 and STAT5 in STAT3-deficient cohorts. IL-27 induced not only proinflammatory responses including up-regulation of ICAM-1, T-box expressed in T cells, and IL-12Rbeta2 and Th1 differentiation, but also anti-inflammatory responses including suppression of proinflammatory cytokine production such as IL-2, IL-4, and IL-13 even in STAT3-deficient naive CD4+ T cells. In contrast, IL-27 augmented c-Myc and Pim-1 expression and induced cell proliferation in wild-type naive CD4+ T cells but not in STAT3-deficient cohorts. Moreover, IL-27 failed to activate STAT3, augment c-Myc and Pim-1 expression, and induce cell proliferation in pro-B BaF/3 transfectants expressing mutant gp130, in which the putative STAT3-binding four Tyr residues in the YXXQ motif of the cytoplasmic region was replaced by Phe. These results suggest that STAT3 is activated through gp130 by IL-27 and is indispensable to IL-27-mediated cell proliferation but not to IL-27-induced Th1 differentiation and suppression of proinflammatory cytokine production. Thus, IL-27 may be a cytokine, which activates both STAT1 and STAT3 through distinct receptor subunits, WSX-1 and gp130, respectively, to mediate its individual immune functions.

Cutting edge: IL-27 is a potent inducer of IL-10 but not FoxP3 in murine T cells

The cytokine IL-27 is important for restricting inflammation in response to a wide variety of immune challenges. In this study, we demonstrate that IL-27 induces expression of the anti-inflammatory cytokine IL-10 by CD4+ and CD8+ T cells. IL-27 relied upon the Th1 transcription factor STAT1 to induce IL-10+IFN-gamma+FoxP3- Th1 cells, which were recently shown to be key negative regulators during certain infections. Il27ra-/- mice generated fewer IL-10+ T cells during both Listeria monocytogenes infection and experimental autoimmune encephalomyelitis. The data presented here indicate a novel mechanism for the induction of IL-10 expression by T cells and provide a mechanistic basis for the suppressive effects of IL-27.

New complexities in helper T cell fate determination and the implications for autoimmune diseases

Recently, new complexities in cell fate decision for helper T cells have emerged. One new lineage, which has come to be called Th17 cells, selectively produces proinflammatory cytokines including interleukin-17 (IL-17, A and F), IL-21, and IL-22. In conjunction with transforming growth factor beta-1 (TGFbeta-1), IL-6, IL-21, and IL-23, which activate the transcription factor, signal transducer, and activator of transcription 3 (Stat3), the expression of another transcription factor, retinoic acid-related orphan receptor-gammat (RORgammat) leads to the differentiation of Th17 cells in mice. Other cytokines including IL-2, IL-4, interferon-gamma (IFN-gamma), and IL-27 inhibit Th17 differentiation. However, IL-2 acting with TGFbeta-1 induces differentiation of naïve CD4+ T cells to become regulatory T cells (Tregs). Th17 cells are now known to play an important role not only in the pathogenesis of inflammation and autoimmune diseases, but also host defense against extracellular bacteria. Conversely, extensive data substantiate the role of Tregs as essential in maintenance of peripheral tolerance. Selectively targeting Tregs and Th17 cells are likely to be important strategies in the treatment of inflammatory and autoimmune diseases in humans.

Resolvin E1 regulates interleukin 23, interferon-gamma and lipoxin A4 to promote the resolution of allergic airway inflammation

Interleukin 23 (IL-23) is integral to the pathogenesis of chronic inflammation. The resolution of acute inflammation is an active process mediated by specific signals and mediators such as resolvin E1 (RvE1). Here we provide evidence that RvE1, in nanogram quantities, promoted the resolution of inflammatory airway responses in part by directly suppressing the production of IL-23 and IL-6 in the lung. Also contributing to the pro-resolution effects of RvE1 treatment were higher concentrations of interferon-gamma in the lungs of RvE1-treated mice. Our findings indicate a pivotal function for IL-23 and IL-6, which promote the survival and differentiation of IL-17-producing T helper cells, in maintaining inflammation and also identify an RvE1-initiated resolution program for allergic airway responses.

Lipopolysaccharides from Bordetella pertussis and Bordetella parapertussis differently modulate human dendritic cell functions resulting in divergent prevalence of Th17-polarized responses

Bordetella pertussis and B. parapertussis are the etiological agents of pertussis, yet the former has a higher incidence and is the cause of a more severe disease, in part due to pertussis toxin. To identify other factors contributing to the different pathogenicity of the two species, we analyzed the capacity of structurally different lipooligosaccharide (LOS) from B. pertussis and LPS from B. parapertussis to influence immune functions regulated by dendritic cells. Either B. pertussis LOS and B. parapertussis LPS triggered TLR4 signaling and induced phenotypic maturation and IL-10, IL-12p40, IL-23, IL-6, and IL-1beta production in human monocyte-derived dendritic cells (MDDC). B. parapertussis LPS was a stronger inducer of all these activities as compared with B. pertussis LOS, with the notable exception of IL-1beta, which was equally produced. Only B. parapertussis LPS was able to induce IL-27 expression. In addition, although MDDC activation induced by B. parapertussis LPS was greatly dependent on soluble CD14, B. pertussis LOS activity was CD14-independent. The analysis of the intracellular pathways showed that B. parapertussis LPS and B. pertussis LOS equally induced IkappaBalpha and p38 MAPK phosphorylation, but B. pertussis LOS triggered ERK1/2 phosphorylation more rapidly and at higher levels than B. parapertussis LPS. Furthermore, B. pertussis LOS was unable to induce MyD88-independent gene induction, which was instead activated by B. parapertussis LPS, witnessed by STAT1 phosphorylation and induction of the IFN-dependent genes, IFN regulatory factor-1 and IFN-inducible protein-10. These differences resulted in a divergent regulation of Th cell responses, B. pertussis LOS MDDC driving a predominant Th17 polarization. Overall, the data observed reflect the different structure of the two LPS and the higher Th17 response induced by B. pertussis LOS may contribute to the severity of pertussis in humans.

Engagement of the type I interferon receptor on dendritic cells inhibits T helper 17 cell development: role of intracellular osteopontin

Mechanisms that prevent inappropriate or excessive interleukin-17-producing T helper (Th17) cell responses after microbial infection may be necessary to avoid autoimmunity. Here, we define a pathway initiated by engagement of type I IFN receptor (IFNAR) expressed by dendritic cells (DC) that culminated in suppression of Th17 cell differentiation. IFNAR-dependent inhibition of an intracellular translational isoform of Osteopontin, termed Opn-i, derepressed interleukin-27 (IL-27) secretion and prevented efficient Th17 responses. Moreover, Opn-i expression in DC and microglia regulated the type and intensity of experimental autoimmune encephalomyelitis (EAE). Mice containing DC deficient in Opn-i produced excessive amounts of IL-27 and developed a delayed disease characterized by an enhanced Th1 response compared with the dominant Th17 response of Opn-sufficient mice. Definition of the IFNAR-Opn-i axis that controls Th17 development provides insight into regulation of Th cell sublineage development and the molecular basis of type I interferon therapy for MS and other autoimmune diseases.

IL-17A inhibits the expansion of IL-17A-producing T cells in mice through "short-loop" inhibition via IL-17 receptor

IL-23 and IL-17A regulate granulopoiesis through G-CSF, the main granulopoietic cytokine. IL-23 is secreted by activated macrophages and dendritic cells and promotes the expansion of three subsets of IL-17A-expressing neutrophil-regulatory T (Tn) cells; CD4(-)CD8(-)alphabeta(low), CD4(+)CD8(-)alphabeta(+) (Th17), and gammadelta(+) T cells. In this study, we investigate the effects of IL-17A on circulating neutrophil levels using IL-17R-deficient (Il17ra(-/-)) mice and Il17ra(-/-)Itgb2(-/-) mice that lack both IL-17R and all four beta(2) integrins. IL-17R deficiency conferred a reduction in neutrophil numbers and G-CSF levels, as did Ab blockade against IL-17A in wild-type mice. Bone marrow transplantation revealed that IL-17R expression on nonhemopoietic cells had the greatest effects on regulating blood neutrophil counts. Although circulating neutrophil numbers were reduced, IL-17A expression, secretion, and the number of IL-17A-producing Tn cells were elevated in Il17ra(-/-) and Il17ra(-/-)Itgb2(-/-) mice, suggesting a negative feedback effect through IL-17R. The negative regulation of IL-17A-producing T cells and IL-17A and IL-17F gene expression through the interactions of IL-17A or IL-17F with IL-17R was confirmed in splenocyte cultures in vitro. We conclude that IL-17A regulates blood neutrophil counts by inducing G-CSF production mainly in nonhemopoietic cells. IL-17A controls the expansion of IL-17A-producing Tn cell populations through IL-17R.

Interleukin 10 suppresses Th17 cytokines secreted by macrophages and T cells

IL-17 and IL-22 are typical cytokines produced by the Th17 T cell subset, but it is unclear if Th17 cytokines can be produced by other cell types. We demonstrate that IL-10-deficient and IL-10R-deficient macrophages stimulated with lipopolysaccharide produce high levels of IL-17 and IL-22. Addition of exogenous IL-10 to IL-10-deficient macrophages abolished IL-17 production. When IL-10-deficient and IL-10R-deficient splenocytes were cultured under Th17 polarizing conditions, the population of IL-17-producing cells was increased and the cultures produced significantly higher levels of IL-17 and IL-22. The addition of recombinant IL-10 to IL-10-deficient splenocytes significantly decreased the percentage of IL-17-producing CD4(+) T cells. Finally, the mRNA for the Th17 transcription factor retinoic acid-related orphan receptor (ROR)gammat was significantly elevated in IL-10-deficient spleen cells and macrophages. These data demonstrate that Th17 cytokines and RORgammat are also expressed in macrophages and that IL-10 negatively regulates the expression of Th17 cytokines and RORgammat by both macrophages and T cells.

The interleukin-23/interleukin-17 axis in spondyloarthritis

PURPOSE OF REVIEW

To inform readers of recent advances in our understanding of the development and function of Th17 T cells and emerging data suggesting that the interleukin-23/interleukin-17 axis may be involved in the pathogenesis of spondyloarthritis.

RECENT FINDINGS

The discovery of CD4+ Th17 T cells and the interleukin-23/interleukin-17 axis has challenged existing paradigms and the role of Th1 T cells in many autoimmune diseases. The development and cytokine profile of Th17 T cells differs in mice and humans. In humans, interleukin-23 synergizes with interleukin-6 and interleukin-1 to promote Th17 development. In mice, transforming growth factor-beta and interleukin-6 are critical, whereas interleukin-23 is more important at later stages promoting interleukin-17 production. In mice, CD4+ cells producing interferon-gamma appear to be distinct from interleukin-17-producing cells, while in humans cells secreting both cytokines have been observed. Growing evidence from animal models, cytokine analyses of patient fluids, and whole-genome association studies suggest that the interleukin-23/interleukin-17 axis plays an important role in spondyloarthritis pathogenesis. Possible links between an HLA-B27-induced unfolded protein response and activation of the interleukin-23/interleukin-17 axis have been observed in animal models and may contribute to the development of the spondyloarthritis phenotype.

SUMMARY

Activation of the interleukin-23/interleukin-17 axis in spondyloarthritis has important therapeutic implications.

The type I IFN induction pathway constrains Th17-mediated autoimmune inflammation in mice

IFN-beta, a type I IFN, is widely used for the treatment of MS. However, the mechanisms behind its therapeutic efficacy are not well understood. Using a murine model of MS, EAE, we demonstrate that the Th17-mediated development of autoimmune disease is constrained by Toll-IL-1 receptor domain-containing adaptor inducing IFN-beta-dependent (TRIF-dependent) type I IFN production and its downstream signaling pathway. Mice with defects in TRIF or type I IFN receptor (IFNAR) developed more severe EAE. Notably, these mice exhibited marked CNS inflammation, as manifested by increased IL-17 production. In addition, IFNAR-dependent signaling events were essential for negatively regulating Th17 development. Finally, IFN-beta-mediated IL-27 production by innate immune cells was critical for the immunoregulatory role of IFN-beta in the CNS autoimmune disease. Together, our findings not only may provide a molecular mechanism for the clinical benefits of IFN-beta in MS but also demonstrate a regulatory role for type I IFN induction and its downstream signaling pathways in limiting Th17 development and autoimmune inflammation.

TH17 cells in development: an updated view of their molecular identity and genetic programming

Following activation, CD4+ T cells differentiate into different lineages of helper T (T(H)) cells that are characterized by distinct developmental regulation and biological functions. T(H)17 cells have recently been identified as a new lineage of effector T(H) cells, and they have been shown to be important in immune responses to infectious agents, as well as in various immune diseases. Over the past two to three years, there has been a rapid progress in our understanding of the differentiation programme of T(H)17 cells. Here, I summarize our current knowledge of the unique gene expression, cytokine-mediated regulation and transcriptional programming of T(H)17 cells, and provide my personal perspectives on the future studies that are required to elucidate this lineage in more detail.

Induction and effector functions of T(H)17 cells

T helper (T(H)) cells constitute an important arm of the adaptive immune system because they coordinate defence against specific pathogens, and their unique cytokines and effector functions mediate different types of tissue inflammation. The recently discovered T(H)17 cells, the third subset of effector T helper cells, have been the subject of intense research aimed at understanding their role in immunity and disease. Here we review emerging data suggesting that T(H)17 cells have an important role in host defence against specific pathogens and are potent inducers of autoimmunity and tissue inflammation. In addition, the differentiation factors responsible for their generation have revealed an interesting reciprocal relationship with regulatory T (T(reg)) cells, which prevent tissue inflammation and mediate self-tolerance.

Antagonizing dopamine D1-like receptor inhibits Th17 cell differentiation: preventive and therapeutic effects on experimental autoimmune encephalomyelitis

Five types of dopamine receptors, termed D1 to D5, have been identified to date. The D1 and D5 receptors form the D1-like group that couples with the Galphas class of G proteins, while D2, D3 and D4 form the D2-like group that couples with the Galphai class of G proteins. A D2-like-receptor (D2-like-R) antagonist L750667 induced dendritic cell (DC)-mediated Th17 differentiation. In contrast, a D1-like-R antagonist SCH23390 inhibited DC-mediated Th17 differentiation. The D1-like-Rs were expressed on both DCs and T cells, whereas D2-like-Rs were marginally expressed on CD4+CD45RA+ naïve T cells. In addition, SCH23390 had the ability to prevent experimental autoimmune encephalomyelitis (EAE) in mice. Spleen cells from EAE mice showed decreased IL-17 production, when SCH23390 was administered. Adoptive transfer of DCs treated with SCH23390 successfully prevented EAE. These findings indicate that antagonizing D1-like-Rs on DCs inhibits Th17 differentiation, thereby leading to an amelioration of EAE.

Loss of suppressor of cytokine signaling 1 in helper T cells leads to defective Th17 differentiation by enhancing antagonistic effects of IFN-gamma on STAT3 and Smads

Suppressor of cytokine signaling 1 (SOCS1) is an important negative regulator for cytokines; however, the role of SOCS1 in Th17 differentiation has not been clarified. We generated T cell-specific SOCS1-deficient mice and found that these mice were extremely resistant to a Th17-dependent autoimmune disease model, experimental autoimmune encephalomyelitis. SOCS1-deficient naive CD4(+) T cells were predominantly differentiated into Th1 and poorly into Th17 in vitro. These phenotypes were canceled in IFN-gamma(-/-) background, suggesting that a large amount of IFN-gamma in SOCS1-deficient T cells suppressed Th17 differentiation. IL-6 plus TGF-beta enhanced retinoic acid receptor-related orphan receptor (ROR)-gammat expression and suppressed IFN-gamma production in wild-type T cells, whereas these effects were severely impaired in SOCS1-deficient T cells. These phenotypes can be partly explained by STAT3 suppression by enhanced SOCS3 induction through hyper-STAT1 activation in SOCS1-deficient T cells. In addition, SOCS1-deficient T cells were much less sensitive to TGF-beta. Suppression of Th1 differentiation by TGF-beta was impaired in SOCS1-deficient T cells. TGF-beta-mediated Smad transcriptional activity was severely inhibited in SOCS1-deficient cells in the presence of IFN-gamma. Such impairment of TGF-beta functions were not observed in SOCS3-overexpressed cells, indicating that suppression of Smads was independent of SOCS3. Therefore, SOCS1 is necessary for Th17 differentiation by suppressing antagonistic effect of IFN-gamma on both STAT3 and Smads. Induction of SOCS3 can partly explain IFN-gamma-mediated STAT3 suppression, while other mechanism(s) will be involved in IFN-gamma-mediated Smad suppression. SOCS1-deficient T cells will be very useful to investigate the molecular mechanism for the STAT1-mediated suppression of Th17 development.

Interleukin 27 signaling pathways in regulation of immune and autoimmune responses

Cytokine-mediated immunity plays a crucial role in pathogenesis of various diseases including autoimmune disease. Recently, interleukin 27 was identified, which along with interleukin 23 belongs to the interleukin 12 cytokine family. Interleukin 27 is pivotal for the induction of T helper 1 responses. Recent studies, however, revealed that interleukin 27 has an immunosuppressive property. In interleukin 27 receptor-deficient mice, various pro-inflammatory cytokines were over produced resulting in excess of immune responses. The immunosuppressive effects of interleukin 27 depend on suppression of interleukin 2 production, inhibition of the development of T helper 17 cells (a newly identified inflammatogenic T helper population), and induction of interleukin 10 production. Activation of signal transducers and activators of transcription 1 and 3 is critical in the immunosuppressive function of interleukin 27. Interleukin 27 suppresses some diseases of autoimmune or allergic origin, demonstrating its promising potential in therapy of diseases mediated by inflammatory cytokines.

IL-27 activates human monocytes via STAT1 and suppresses IL-10 production but the inflammatory functions of IL-27 are abrogated by TLRs and p38

IL-27 is a member of the IL-12 family of cytokines that activates the Jak-STAT signaling pathway in a context-dependent manner and has pleiotropic effects on acquired immunity. IL-27 has the capacity to promote early stages of Th1 generation, but recent evidence has suggested a predominant suppressive effect on Th1, Th2, and Th17 differentiation. Although modest suppressive effects of IL-27 on myeloid lineage cells have been observed, there is limited knowledge about the role of IL-27 in the regulation of innate immunity. In this study we report that although in resting murine macrophages IL-27 had minimal if any effects, in resting human monocytes IL-27 had profound proinflammatory functions. IL-27 activated a STAT1-dominant pattern of signaling in human monocytes with the consequent activation of STAT1-dependent inflammatory target genes. IL-27 primed monocytes for augmented responses to TLR stimulation in a STAT1-dependent manner, altered IL-10 signaling, and attenuated IL-10-induced gene expression. Strikingly, IL-27 strongly suppressed TLR-induced IL-10 production in human monocytes. However, the proinflammatory effects of IL-27 on human monocytes were rapidly abrogated by LPS via a p38-mediated mechanism that inhibited IL-27 signaling. Our findings identify a predominantly proinflammatory function for IL-27 in human monocytes and suggest a mechanism by which the activating effects of IL-27 on innate immunity are attenuated as an immune response proceeds and IL-27 transitions to predominantly suppressive effects on acquired immunity.

Th17 and allergy

The identification of novel helper T (Th) cell subsets, i.e., IL-17-producing Th cells (Th17 cells) and regulatory T cells (Treg cells), provided new insight into our understanding of the molecular mechanisms involved in the development of infectious and autoimmune diseases as well as immune responses, and thus led to revision of the classic Th1/Th2 paradigm. Several current lines of evidence from gene-deficient mice indicate that IL-17 and Th17 cells, but not IFN-gamma and Th1 cells, are responsible for the development of autoimmune diseases such as murine arthritis and encephalomyelitis, which have classically been considered to be Th1-mediated disorders. Th17 cells may also contribute to the pathogenesis of classically recognized Th2-mediated allergic disorders. In this review, we summarize the current knowledge regarding IL-17 and Th17 cells and discuss their potential roles in the pathogenesis of allergic disorders.

Th17 Cells and autoimmune encephalomyelitis (EAE/MS)

Multiple sclerosis (MS) is a CD4+ T cell-mediated autoimmune disease affecting the central nervous system. It was largely accepted that Th1 cells driven by IL-12 were pathogenic T cells in human MS and experimental autoimmune encephalomyelitis, an animal model of MS. Recent data have established that IL-17-producing CD4+ T cells, driven by IL-23 and referred to as Th17 cells, play a pivotal role in the pathogenesis of EAE. A combination of TGF-beta and IL-6 induce Th17 cell lineage commitment via expression of transcription factor RORgammat. Th17 cells and induced Foxp3+ T regulatory cells are in reciprocal position in the T cell lineage commitment governed by TGF-beta and IL-6. The vitamin A metabolite retinoic acid is involved in this process via TGF-beta dependent induction of Foxp3. We have demonstrated that human Th17 cells could be identified as CCR2+ CCR5- memory CD4+ T cells. It is becoming clear that IL-23/Th17 axis also plays an important role in the pathogenesis of various human autoimmune diseases including MS. Additionally, accumulating evidences raise a possibility that CCR2 on Th17 cells may be a therapeutic target in MS.

Th17 cells in human disease

SUMMARY

Our understanding of the role of T cells in human disease is undergoing revision as a result of the discovery of T-helper 17 (Th17) cells, a unique CD4(+) T-cell subset characterized by production of interleukin-17 (IL-17). IL-17 is a highly inflammatory cytokine with robust effects on stromal cells in many tissues. Recent data in humans and mice suggest that Th17 cells play an important role in the pathogenesis of a diverse group of immune-mediated diseases, including psoriasis, rheumatoid arthritis, multiple sclerosis, inflammatory bowel disease, and asthma. Initial reports also propose a role for Th17 cells in tumorigenesis and transplant rejection. Important differences, as well as many similarities, are emerging when the biology of Th17 cells in the mouse is compared with corresponding phenomena in humans. As our understanding of human Th17 biology grows, the mechanisms underlying many diseases are becoming more apparent, resulting in a new appreciation for both previously known and more recently discovered cytokines, chemokines, and feedback mechanisms. Given the strong association between excessive Th17 activity and human disease, new therapeutic approaches targeting Th17 cells are highly promising, but the potential safety of such treatments may be limited by the role of these cells in normal host defenses against infection.

Advances in understanding the anti-inflammatory properties of IL-27

Initial studies on the biology of IL-27 provided evidence of a role for this cytokine in the initiation of Th1 responses; however, subsequent work using models of pathogen-induced and autoimmune inflammation have indicated that IL-27 has broad inhibitory effects on Th1, Th2 and Th17 subsets of T cells as well as the expansion of inducible regulatory T cells. While, the aim of this review is to highlight the functions of IL-27 in the context of inflammation it will also serve to elaborate on the molecular mechanisms involved in the production of this cytokine. The initial description of IL-27 indicated that classical antigen-presenting cells such as macrophages and dendritic cells produce IL-27, however, the agonists and signaling pathways involved in activating transcription of the two subunits of IL-27, p28 and EBV-induced gene 3 (EBI3) have only recently been described.

Epstein-Barr virus-induced gene 3 negatively regulates IL-17, IL-22 and RORgamma t

Epstein-Barr virus-induced gene 3 (EBI3) associates with p28 to form IL-27 and with IL-12p35 to form IL-35. IL-27Ralpha(-/-) mice studies indicate that IL-27 negatively regulates Th17 cell differentiation. However, no EBI3, p28 or p35-deficiency studies that directly address the role of EBI3, p28 or p35 on Th17 cells have been done. Here, we demonstrate that spleen cells derived from EBI3(-/-) mice produce significantly higher levels of IL-17 as well as IL-22 upon stimulation with OVA. In vitro derived EBI3(-/-) Th17 cells also produced significantly higher levels of IL-17 and IL-22 than WT cells. The frequency of IL-17-producing cells was also elevated when EBI3(-/-) cells were cultured under Th17 conditions. In addition, spleen cells from EBI3(-/-) mice immunized with Listeria monocytogenes produced significantly elevated levels of IL-17 and IL-22. Furthermore, the Th17 transcription factor RORgamma t was significantly enhanced in EBI3(-/-) cells. Finally, EBI3(-/-) mice exhibited a reduced bacterial load following an acute challenge with L. monocytogenes or a re-challenge of previously immunized mice, suggesting that EBI3 negatively regulates both innate and adaptive immunity. Taken together, these data provide direct evidence that EBI3 negatively regulates the expression of IL-17, IL-22 and RORgamma t as well as protective immunity against L. monocytogenes.

Psoriasis vulgaris lesions contain discrete populations of Th1 and Th17 T cells

The importance of T helper 17 (Th17) cells in inflammation and autoimmunity is now being appreciated. We analyzed psoriasis skin lesions and peripheral blood for the presence of IL-17-producing T cells. We localized Th17 cells predominantly to the dermis of psoriasis skin lesions, confirmed that IL-17 mRNA increased with disease activity, and demonstrated that IL-17 mRNA expression normalized with cyclosporine therapy. IL-22 mRNA expression mirrored IL-17 and both were downregulated in parallel with keratin 16. Th17 cells are a discrete population, separate from Th1 cells (which are also in psoriasis lesions), and Th2 cells. Our findings suggest that psoriasis is a mixed Th1 and Th17 inflammatory environment. Th17 cells may be proximal regulators of psoriatic skin inflammation, and warrant further attention as therapeutic targets.

Regulation of FoxP3 regulatory T cells and Th17 cells by retinoids

Vitamin A has both positive and negative regulatory functions in the immune system. While vitamin A is required for normal formation of immune cells and epithelial cell barriers, vitamin A deficiency can lead to increased inflammatory responses and tissue damage. The mechanism with which vitamin A and its metabolites such as retinoids negatively regulate inflammatory responses has not been clearly defined. Recently, it has been established that retinoids promote the generation of immune-suppressive FoxP3⁺ regulatory T cells while they suppress the T cell differentiation into inflammatory Th17 cells in the periphery such as intestine. These novel functions of retinoids provide a potentially important immune regulatory mechanism. In this review, we discuss the functions of retinoids in the development of the FoxP3⁺ cells and Th17 cells, the phenotype and functions of retinoid-induced FoxP3⁺ T cells, and the impact of retinoid-induced FoxP3⁺ T cells on the immune tolerance.

Amino acid copolymer-specific IL-10-secreting regulatory T cells that ameliorate autoimmune diseases in mice

IL-10-secreting regulatory T cell lines specific to glatiramer acetate [poly(Y,E,A,K)n] or poly(Y,F,A,K)n have been established from the enlarged spleen and lymph nodes that result from copolymer treatment of SJL mice in which experimental autoimmune encephalomyelitis was induced by PLP139-151. These CD4+CD25+T cell lines secrete high levels of IL-10 and IL-13 but only small amounts of IL-4 and virtually no TGF-beta, IL-17, IL-6, IFN-gamma, or TNF-alpha. Their phenotypes are particularly characterized by the absence of Foxp3 and the presence of two TNFR family members, CD30 and GITR. The lines proliferated specifically to the immunizing copolymers but were autoantigen-nonspecific, in that the same T cell line could suppress autoimmunity induced by three different autoantigens in SJL mice, i.e., PLP139-151(EAE), MBP85-99 (EAE), and bovine peripheral nerve myelin (experimental autoimmune neuritis), indicating they function by bystander suppression.

IL-27R deficiency delays the onset of colitis and protects from helminth-induced pathology in a model of chronic IBD

Members of the IL-6/IL-12 cytokine family play central roles in Crohn's disease. The present findings demonstrate that IL-27, a close relative of IL-12 and IL-23, can promote the onset of colitis in mice. We report that, compared with IL-10-deficient animals, which succumb to chronic intestinal disease at 3-6 months of age, mice lacking both IL-10 and the IL-27R (IL-27R/WSX-1) exhibit delayed pathology and prolonged survival (>1 year). Moreover, unlike highly susceptible IL-10-deficient counterparts, they were able to clear infection with Trichuris muris, a colon-dwelling nematode. In both models of intestinal inflammation, improved clinical outcome was associated with reduced inflammation and profound attenuation of T(h)1 responses and, consistent with these in vivo findings, we confirmed that during in vitro differentiation, IL-27 directly promotes CD4(+) T cell IFN-gamma production through effects on Tbet, a key T(h)1 transcription factor. We also found that its ability to suppress T(h)2 responses, which was clearly evident in helminth-infected IL-10-/-IL-27R-/- mice, was largely Tbet independent. Taken together, these studies demonstrate that, in the absence of IL-10, IL-27 can promote T(h)1-type and suppress T(h)2-type intestinal inflammation but, ultimately, is not required for the development of inflammatory bowel disease.

Commensal gut flora drives the expansion of proinflammatory CD4 T cells in the colonic lamina propria under normal and inflammatory conditions

We tested in B6 mice whether the local expansion of CD4 T cells producing proinflammatory cytokines including IL-17 (Th17 cells) in the colonic lamina propria (cLP) depends on the commensal microflora. High numbers of CD4 Th17 cells were found in the lamina propria of the ileum and colon but not the duodenum, jejunum, mesenteric lymph nodes, spleen, or liver of specific pathogen-free (SPF) mice. The microflora is required for the accumulation of cytokine (IL-17, IFN-gamma, TNF-alpha, IL-10)-producing CD4 T cells in the cLP because only low numbers of cytokine-producing cLP CD4 T cells were found in syngeneic (age- and sex-matched) germfree mice. The fraction of cLP Th17 cells was higher in (type I and type II) IFN- but not IL-4- or IL-12p40-deficient SPF congenics. cLP CD4 Th17 cells produce IL-17 but not IFN-gamma, TNF-alpha, IL-4, or IL-10. cLP CD4 Th17 cells accumulate locally in colitis induced by adoptive transfer of IFN-gamma+/+ or IFN-gamma-/- CD4 T cells into congenic SPF (but not germfree) RAG-/- hosts. In this colitis model, cLP CD4 T cells that "spontaneously" produce IL-17 progressively increase in number in the inflamed cLP, and increasing serum IL-17 levels appear as the disease progresses. Commensal bacteria-driven, local expansion of cLP CD4 Th17 cells may contribute to the pathogenesis of this inflammatory bowel disease.

IL-27 induces a Th1 immune response and susceptibility to experimental arthritis

IL-27 is the newest member of the cytokine family comprised of IL-12 and IL-23. IL-27 was originally described as a cytokine that along with IL-12 induces the differentiation of naive precursor T cells into Th1 effector cells. This activity has been called into question based on evidence in infectious disease and autoimmune models in which IL-27 is not absolutely required for the generation of IFN-gamma, and IL-27 plays a regulatory role in controlling inflammation. We have previously reported in proteoglycan-induced arthritis (PGIA), a model of rheumatoid arthritis, that severe arthritis is dependent on the production of IFN-gamma. In this study, we report that IL-27 was expressed in spleen and joint tissues of arthritic mice. We determined the involvement of IL-27 in PGIA by assessing the progression of arthritis in IL-27R-/- mice. Development of arthritis in IL-27R-/- mice was delayed and severity reduced in comparison with IL-27R+/+ littermate controls. Histology confirmed a reduction in joint cellularity, cartilage destruction, and bone erosion. Diminished arthritis was associated with fewer T cells producing IFN-gamma and decreased IFN-gamma secretion overtime. Moreover, the frequency of IL-4- and IL-17-expressing T cells and the production of IL-4 and IL-17 were similar in IL-27R-/- mice and controls. Our results indicate that IL-27 is critically involved in the induction of inflammation in PGIA. IL-27 functions by inducing the differentiation of IFN-gamma-producing T cells in vivo that are essential for the development of arthritis.

Cutting edge: T-bet and IL-27R are critical for in vivo IFN-gamma production by CD8 T cells during infection

CD8+ T cells are a major source of IFN-gamma, a key effector cytokine in immune responses against many viruses and protozoa. Although the transcription factor T-bet is required for IFN-gamma expression in CD4+ T cells, it is reportedly dispensable in CD8+ T cells, where the transcription factor Eomesodermin is thought to be sufficient. The diverse functions of IFN-gamma are mediated through the IFN-gammaR and STAT1. In CD4+ T cells, STAT1 appears to be critical for the activation of T-bet and IFN-gamma, suggesting an IFN-gamma-dependent positive feedback loop. However, STAT1 can also be activated by other cytokines, including IL-27. In the present study we show that, in contrast to in vitro conditions and the prevailing paradigm, T-bet is critical for the in vivo IFN-gamma production by CD8+ T cells upon infection of mice with diverse pathogens. Whereas IFN-gammaR signals are dispensable for the T-bet-dependent IFN-gamma production, direct IL-27Ralpha signals are critical.

Regulatory mechanisms of helper T cell differentiation: new lessons learned from interleukin 17 family cytokines

Interleukin 17 (IL-17) family consists of six cytokines in mammals. Among them, IL-17 and IL-17F are expressed by a novel subset of CD4+ helper T (Th) cells and play critical function in inflammation and autoimmunity. On the other hand, IL-17E, also called IL-25, has been associated with allergic responses. Here we summarize recent work by us as well as other investigators in understanding the regulation and function of these three cytokines. From these studies, IL-17 family cytokines may serve as novel targets for pharmaceutical intervention of immune and inflammatory diseases.

IL-22 mediates mucosal host defense against Gram-negative bacterial pneumonia

Emerging evidence supports the concept that T helper type 17 (T(H)17) cells, in addition to mediating autoimmunity, have key roles in mucosal immunity against extracellular pathogens. Interleukin-22 (IL-22) and IL-17A are both effector cytokines produced by the T(H)17 lineage, and both were crucial for maintaining local control of the Gram-negative pulmonary pathogen, Klebsiella pneumoniae. Although both cytokines regulated CXC chemokines and granulocyte colony-stimulating factor production in the lung, only IL-22 increased lung epithelial cell proliferation and increased transepithelial resistance to injury. These data support the concept that the T(H)17 cell lineage and its effector molecules have evolved to effect host defense against extracellular pathogens at mucosal sites.

Interleukin-17 in pulmonary host defense

Interleukin (IL)-17A and IL-17F are produced by a novel class of effector alphabeta T cells called Th17 cells as well as gammadelta T cells. alphabeta IL-17-producing T cells are controlled by the transcription factor RORgammat and develop independent of GATA-3, T-bet, Stat 4, and Stat 6. Effector molecules produced by these cells include IL-17A, IL-17F, and IL-22. IL-17A and IL-17F bind to IL-17 receptor (IL-17R) and receptor signaling is critical for host defense against extracellular bacteria by regulating chemokine gradients for neutrophil emigration into infected tissue sites as well as via regulation of host granulopoiesis. Furthermore, it has recently been shown that IL-17 and IL-22 regulate the production of antimicrobial proteins in epithelium. Although Th17 cells are important in mucosal host defense, in the setting of retained antigenic stimulation, such as in the setting of asthma or chronic infection, such as in cystic fibrosis, or in the setting of autoimmunity, these cells can mediate immunopathology.

Adverse functions of IL-17A in experimental sepsis

IL-17A is a proinflammatory cytokine produced by a variety of cells. In the current study, we examined the role of IL-17A in sepsis induced in mice by cecal ligation and puncture (CLP). IL-17A levels, which rose time-dependently in plasma after CLP, were not affected in the absence of alphabeta T cells or neutrophils. In sharp contrast, gammadelta T cell-knockout or gammadelta T cell-depleted mice displayed baseline IL-17A plasma levels after CLP. Neutralization of IL-17A by two different antibodies improved sepsis (survival from approximately 10% to nearly 60%). Unexpectedly, antibody treatment was protective, even when administration of anti-IL-17A was delayed for up to 12 h after CLP. These protective effects of IL-17A blockade were associated with substantially reduced levels of bacteremia together with significant reductions of systemic proinflammatory cytokines and chemokines in plasma. In vitro incubation of mouse peritoneal macrophages with lipopolysaccharide (LPS) in the copresence of IL-17A substantially increased the production of TNF-alpha, IL-1beta, and IL-6 by these cells. These data suggest that, during experimental sepsis, gammadelta T cell-derived IL-17A promotes high levels of proinflammatory mediators and bacteremia, resulting in enhanced lethality. IL-17A may be a potential therapeutic target in sepsis.

IL-23 and IL-17 in tuberculosis

Tuberculosis is a chronic disease requiring the constant expression of cellular immunity to limit bacterial growth. The constant expression of immunity also results in chronic inflammation, which requires regulation. While IFN-gamma-producing CD4+ T helper cells (Th1) are required for control of bacterial growth they also initiate and maintain a mononuclear inflammatory response. Other T cell subsets are induced by Mycobacterium tuberculosis (Mtb) infection including those able to produce IL-17 (Th17). IL-17 is a potent inflammatory cytokine capable of inducing chemokine expression and recruitment of cells to parenchymal tissue. Both the IL-17 and the Th17 response to Mtb are largely dependent upon IL-23. Although both Th17 and Th1 cells are induced following primary infection with Mtb, the protective response is significantly altered in the absence of Th1 cells but not in the absence of Th17. In contrast, in vaccinated animals the absence of memory Th17 cells results in loss of both the accelerated memory Th1 response and protection. Th1 and Th17 responses cross-regulate each other during mycobacterial infection and this may be important for immunopathologic consequences not only in tuberculosis but also other mycobacterial infections.

Dendritic cells and cytokines in human inflammatory and autoimmune diseases

Dendritic cells (DCs) produce cytokines and are susceptible to cytokine-mediated activation. Thus, interaction of resting immature DCs with TLR ligands, for example nucleic acids, or with microbes leads to a cascade of pro-inflammatory cytokines and skewing of T cell responses. Conversely, several cytokines are able to trigger DC activation (maturation) via autocrine, for example TNF and plasmacytoid DCs, and paracrine, for example type I IFN and myeloid DCs, pathways. By controlling DC activation, cytokines regulate immune homeostasis and the balance between tolerance and immunity. The increased production and/or bioavailability of cytokines and associated alterations in DC homeostasis have been implicated in various human inflammatory and autoimmune diseases. Targeting these cytokines with biological agents as already is the case with TNF and IL-1 represents a success of immunology and the coming years will expand the range of cytokines as therapeutic targets in autoinflammatory and autoimmune pathology.

The human response to infection is associated with distinct patterns of interleukin 23 and interleukin 27 expression

OBJECTIVE

The development and progression of severe sepsis is related to a deficiency in pro-inflammatory cytokine production, characterised by lesser IFNgamma levels, which are not explained by variations in levels of the main putative regulator of IFNgamma, namely IL-12. As alternative regulators of IFNgamma may be of greater importance in human sepsis, we investigated the hypothesis that the development of severe sepsis is related to variations in IL-18, IL-23 and IL-27 gene expression.

DESIGN AND SETTING

A prospective observational trial in a mixed intensive care unit (ICU) and hospital wards in a university teaching hospital.

PATIENTS AND PARTICIPANTS

Sixty-two ICU patients with severe sepsis, 13 bacteraemic patients with no acute critical illness, and 10 healthy controls.

MEASUREMENTS AND RESULTS

All subjects were assayed for IL-18, IL-23 and IL-27 mRNA levels in peripheral blood. IL-27 mRNA levels distinguished between the three groups, with levels highest in the ICU group, intermediate in the bacteraemic group and lowest in the control group. IL-23 distinguished between the groups, with levels lowest in the ICU group. In late sepsis IL-23 and TNFalpha mRNA levels were directly related. IL-18 mRNA levels did not distinguish between the patient groups.

CONCLUSIONS

We conclude that the deficient pro-inflammatory response in patients with sepsis is expansive and includes deficient IL-23 and excessive IL-27 gene expression. This provides further evidence that upregulation of a cytokine-based immune response is beneficial in sepsis.

How microorganisms tip the balance between interleukin-12 family members

Interleukin-12p70 (IL-12p70) induces T-helper-1-cell responses and IL-23, a related cytokine, is the master switch in several T-cell-mediated inflammatory disorders. IL-27, another member of the IL-12 family, regulates innate and adaptive immune responses. Recently, distinct combinations of transcription factors have been shown to regulate the expression of the genes that encode these three cytokines. Toll-like receptor ligands, in association with other microbial products and endogenous mediators, tip the balance between the expression of IL-12 family members and thereby may control the outcome of T-cell-mediated inflammation. On this basis, we present a novel perspective on the pathogenesis and regulation of inflammatory disorders.

Targeting the development and effector functions of TH17 cells

T helper (TH) cells can assume different phenotypes characterized by the secretion of distinct effector molecules. Interferon-gamma producing TH1 and IL-4 producing TH2 cells have long been recognized as important mediators of host defense, whereas regulatory T cells are known to suppress T cell responses. Recently, TH17 cells were characterized as a novel CD4(+) subset that preferentially produces IL-17, IL-17F, and IL-22 as the signature cytokines. TH17 cells appear to play a critical role in sustaining the inflammatory response and their presence is closely associated with autoimmune disease, which makes them an attractive therapeutic target. In this review, we focus on the mechanisms that regulate the differentiation of naive T cells into TH17 cells and on TH17 effector cytokines, as they represent opportunities for therapeutic intervention.

Innocuous IFNgamma induced by adjuvant-free antigen restores normoglycemia in NOD mice through inhibition of IL-17 production

The role of Th17 cells in type I diabetes (TID) remains largely unknown. Glutamic acid decarboxylase (GAD) sequence 206–220 (designated GAD2) represents a late-stage epitope, but GAD2-specific T cell receptor transgenic T cells producing interferon γ (IFNγ) protect against passive TID. Because IFNγ is known to inhibit Th17 cells, effective presentation of GAD2 peptide under noninflammatory conditions may protect against TID at advanced disease stages. To test this premise, GAD2 was genetically incorporated into an immunoglobulin (Ig) molecule to magnify tolerance, and the resulting Ig-GAD2 was tested against TID at different stages of the disease. The findings indicated that Ig-GAD2 could not prevent TID at the preinsulitis phase, but delayed TID at the insulitis stage. More importantly, Ig-GAD2 sustained both clearance of pancreatic cell infiltration and β-cell division and restored normoglycemia when given to hyperglycemic mice at the prediabetic stage. This was dependent on the induction of splenic IFNγ that inhibited interleukin (IL)-17 production. In fact, neutralization of IFNγ led to a significant increase in the frequency of Th17 cells, and the treatment became nonprotective. Thus, IFNγ induced by an adjuvant free antigen, contrary to its usual inflammatory function, restores normoglycemia, most likely by localized bystander suppression of pathogenic IL-17–producing cells.

IL-27, a novel anti-HIV cytokine, activates multiple interferon-inducible genes in macrophages

OBJECTIVE

IL-27 is a novel anti-HIV cytokine that inhibits HIV-1 replication in both CD4 T cells and monocyte-derived macrophages (MDM) as IFN-alpha does. To elucidate the mechanism of the antiviral activity, we compared the activity and the gene expression profile of IL-27-treated cells with that of IFN-alpha-treated cells.

METHODS

CD4 T cells and monocytes were isolated from peripheral blood mononuclear cells of healthy donors. CD4 T cells were stimulated with phytohemagglutinin, and MDM were induced from monocytes using macrophage-colony stimulating factor. HIV-1 replication was monitored by p24 antigen capture assay. The gene expression profiles were analysed using DNA microarray analysis. The increase in the expression of IFN-inducible genes (IFIG) was confirmed by the Quantigene plex assay.

RESULTS

Both cytokines preferentially inhibited HIV-1 replication in MDM compared with CD4 T cells. Quantitative real time polymerase chain reaction, enzyme-linked immunosorbent assay and neutralization assay using anti-IFN indicated that IFN-alpha, IFN-beta and IFN-gamma had no significant impact on IL-27-mediated HIV inhibition. DNA microarray analysis illustrated that IFN-alpha induced 33 and 18 IFIG in MDM and CD4 T cells, respectively. IL-27 induced 28 IFIG in MDM and five IFIG in CD4 T cells. The quantitative assay confirmed that IL-27 activated genes of RNA-dependent kinase, oligoadenylate synthetase, myxovirus protein, and apolipoprotein B messenger RNA-editing enzyme-catalytic polypeptide-like 3G.

CONCLUSION

IL-27 differentially regulates the gene expression between CD4 T cells and MDM. IL-27 significantly induces antiviral genes in MDM as does IFN-alpha, suggesting that IL-27 inhibits HIV replication in MDM via mechanism(s) similar to that of IFN-alpha.

Interplay of parasite-driven immune responses and autoimmunity

As more facts emerge regarding the ways in which parasite-derived molecules modulate the host immune response, it is possible to envisage how a lack of infection by agents that once infected humans commonly might contribute to the rise in autoimmune disease. Through effects on cells of both the innate and adaptive arms of the immune response, parasites can orchestrate a range of outcomes that are beneficial not only to parasites, in terms of facilitating their life cycles, but also to their host, in limiting pathology.

Th17 cells: a new fate for differentiating helper T cells

Classically naïve CD4(+) have been thought to differentiate into two possible lineages, T helper 1 (Th1) or T helper 2 (Th2) cells. Within this paradigm the pathogenesis of autoimmunity was suggested to predominantly relate to Th1 cells and the production of IFN-gamma. However, there were many aspects of this model that did not seem to fit, not the least of which was that IFN-gamma was protective in some models of autoimmunity. During the past 2 years, remarkable progress has been made to characterize a new lineage of helper T cells. Designated Th17 cells, this lineage selectively produces proinflammatory cytokines including IL-17, IL-21, and IL-22. In the mouse, the differentiation of this new lineage is initiated by TGFbeta-1 and IL-6 and IL-21, which activate Stat3 and induce the expression of the transcription factor retinoic acid-related orphan receptor (RORgammat). IL-23, which also activates Stat3, apparently serves to maintain Th17 cells in vivo. In human cells, IL-1, IL-6, and IL-23 promote human Th17 differentiation, but TGFbeta-1 is reportedly not needed. Emerging data have suggested that Th17 plays an essential role in the host defense against extracellular bacteria and fungi and in pathogenesis of autoimmune diseases. Selectively targeting the Th17 lineage may be beneficial for the treatment of inflammatory and autoimmune diseases.

T helper 17 lineage differentiation is programmed by orphan nuclear receptors ROR alpha and ROR gamma

T cell functional differentiation is mediated by lineage-specific transcription factors. T helper 17 (Th17) has been recently identified as a distinct Th lineage mediating tissue inflammation. Retinoic acid receptor-related orphan receptor gamma (ROR gamma) was shown to regulate Th17 differentiation; ROR gamma deficiency, however, did not completely abolish Th17 cytokine expression. Here, we report Th17 cells highly expressed another related nuclear receptor, ROR alpha, induced by transforming growth factor-beta and interleukin-6 (IL-6), which is dependent on signal transducer and activator of transcription 3. Overexpression of ROR alpha promoted Th17 differentiation, possibly through the conserved noncoding sequence 2 in Il17-Il17f locus. ROR alpha deficiency resulted in reduced IL-17 expression in vitro and in vivo. Furthermore, ROR alpha and ROR gamma coexpression synergistically led to greater Th17 differentiation. Double deficiencies in ROR alpha and ROR gamma globally impaired Th17 generation and completely protected mice against experimental autoimmune encephalomyelitis. Therefore, Th17 differentiation is directed by two lineage-specific nuclear receptors, ROR alpha and ROR gamma.

IL-27 inhibits the development of regulatory T cells via STAT3

Regulatory CD4+ T cells are important for the homeostasis of the immune system and their absence correlates with autoimmune disorders. Here, we investigate the capacity of IL-27, a cytokine with pro- and anti-inflammatory properties, to regulate the generation of transforming growth factor beta (TGFbeta)-inducible forkhead box P3 (Foxp3)-positive regulatory T (Treg) cells. Our results demonstrate that IL-27 inhibits the acquisition of the Treg phenotype at the level of Foxp3, CD25 and CTLA-4 (CD152) expression as well as the suppressive function. In contrast to TGFbeta-induced Treg cells, the cells generated after differentiation in the presence of TGFbeta and IL-27 maintained the ability for IL-2 and tumour necrosis factor alpha (TNFalpha) production. The inhibitory effect of IL-27 on Treg generation was at least partially signal transducer and activator of transcription 3 (STAT3) dependent as examined by targeted STAT3 protein inhibition using small interfering RNA (siRNA), while STAT1-dependent signals seemed to oppose the STAT3 signals. In turn, TGFbeta blocked IL-27-induced T(h)1 differentiation. Thus, IL-27 and TGFbeta mutually control their effects on CD4+ T-cell differentiation, whereby IL-27 favours inflammatory conditions through a STAT3-dependent inhibition of Treg generation.

Differential effects of Th1, monocyte/macrophage and Th2 cytokine mixtures on early gene expression for glial and neural-related molecules in central nervous system mixed glial cell cultures: neurotrophins, growth factors and structural proteins

Background

In multiple sclerosis, inflammatory cells are found in both active and chronic lesions, and it is increasingly clear that cytokines are involved directly and indirectly in both formation and inhibition of lesions. We propose that cytokine mixtures typical of Th1 or Th2 lymphocytes, or monocyte/macrophages each induce unique molecular changes in glial cells.

Methods

To examine changes in gene expression that might occur in glial cells exposed to the secreted products of immune cells, we have used gene array analysis to assess the early effects of different cytokine mixtures on mixed CNS glia in culture. We compared the effects of cytokines typical of Th1 and Th2 lymphocytes and monocyte/macrophages (M/M) on CNS glia after 6 hours of treatment.

Results

In this paper we focus on changes with potential relevance for neuroprotection and axon/glial interactions. Each mixture of cytokines induced a unique pattern of changes in genes for neurotrophins, growth and maturation factors and related receptors; most notably an alternatively spliced form of trkC was markedly downregulated by Th1 and M/M cytokines, while Th2 cytokines upregulated BDNF. Genes for molecules of potential importance in axon/glial interactions, including cell adhesion molecules, connexins, and some molecules traditionally associated with neurons showed significant changes, while no genes for myelin-associated genes were regulated at this early time point. Unexpectedly, changes occurred in several genes for proteins initially associated with retina, cancer or bone development, and not previously reported in glial cells.

Conclusion

Each of the three cytokine mixtures induced specific changes in gene expression that could be altered by pharmacologic strategies to promote protection of the central nervous system.