IL-17 receptor knockout mice have enhanced myelotoxicity and impaired hemopoietic recovery following gamma irradiation

Targeting interleukin-17 in radiation-induced toxicity and cancer progression

Recent strategies to combine chemoradiation with immunotherapy to treat locally advanced lung cancer have improved five-year survival outcomes. However, collateral toxicity to healthy lungs, esophagus, cardiac, and vascular tissue continues to limit the effectiveness of curative-intent thoracic radiation (tRT). It is necessary to gain a deeper comprehension of the fundamental mechanisms underlying inflammation-mediated radiation-induced damage to normal cells. Several cells have been linked in published studies to the release of cytokines and chemokines after radiation therapy. Several inflammatory mediators, such as IL-1, IL-6, TNF-α, and TGF-β, also cause the production of Interleukin-17 (IL-17), a cytokine that is essential for maintaining immunological homeostasis and plays a role in the toxicity caused by radiation therapy. However, currently, the role of IL-17 in RT-induced toxicity in conjunction with cancer progression remains poorly understood. This review provides an overview of the most recent data from the literature implicating IL-17 in radiation-mediated tissue injuries and the efficacy of tRT in lung cancer, as well as its potential as a therapeutic target for interventions to reduce the side effects of tRT with curative intent and to boost an anti-tumor immune response to improve treatment outcomes. IL-17 may also act as a biomarker for predicting the effectiveness of a given treatment as well as the toxicity caused by tRT.

Endosome Traffic Modulates Pro-Inflammatory Signal Transduction in CD4+ T Cells-Implications for the Pathogenesis of Systemic Lupus Erythematosus

Endocytic recycling regulates the cell surface receptor composition of the plasma membrane. The surface expression levels of the T cell receptor (TCR), in concert with signal transducing co-receptors, regulate T cell responses, such as proliferation, differentiation, and cytokine production. Altered TCR expression contributes to pro-inflammatory skewing, which is a hallmark of autoimmune diseases, such as systemic lupus erythematosus (SLE), defined by a reduced function of regulatory T cells (Tregs) and the expansion of CD4⁺ helper T (Th) cells. The ensuing secretion of inflammatory cytokines, such as interferon-γ and interleukin (IL)-4, IL-17, IL-21, and IL-23, trigger autoantibody production and tissue infiltration by cells of the adaptive and innate immune system that induce organ damage. Endocytic recycling influences immunological synapse formation by CD4⁺ T lymphocytes, signal transduction from crosslinked surface receptors through recruitment of adaptor molecules, intracellular traffic of organelles, and the generation of metabolites to support growth, cytokine production, and epigenetic control of DNA replication and gene expression in the cell nucleus. This review will delineate checkpoints of endosome traffic that can be targeted for therapeutic interventions in autoimmune and other disease conditions.

Investigating increased hematopoietic stem cell fitness in a novel mouse model

T-cell acute lymphoblastic leukaemia (T-ALL) is a bone marrow (BM) malignancy affecting children and adults. Typically treated with chemotherapy, leukaemia remains a major death cause in people under 20 years old. Understanding molecularly altered pathways in T-ALL may lead to new therapeutic avenues in the future. Ras pathway dysregulation is common in T-ALL. We have shown elevated expression levels of the Ras guanine nucleotide exchange factor RasGRP1 in T-ALL patients, which results in constant production of active Ras (RasGTP). When leukaemia cell lines are exposed to cytokines, RasGTP levels further increase in a RasGRP1-dependent manner. How overexpressed RasGRP1 may impact primary BM cells has remained unknown. We recently published a new RoLoRiG mouse model that allows for pIpC-induced overexpression of RasGRP1 in haematopoietic cells, which can be traced with an ires-EGFP cassette. This novel model revealed that RasGRP1 overexpression bestows a fitness advantage to haematopoietic stem cells (HSCs) over wild-type cells. Intriguingly, this increased fitness only manifests in native Hematopoiesis, and not in BM transplantation (BMT) assays. In this commentary, we summarize key features of our RoLoRiG model, elaborate on BM niche importance, and discuss differences between native Hematopoiesis and BMT in the context of stem cell metabolism.

Tonic interferon restricts pathogenic IL-17-driven inflammatory disease via balancing the microbiome

Maintenance of immune homeostasis involves a synergistic relationship between the host and the microbiome. Canonical interferon (IFN) signaling controls responses to acute microbial infection, through engagement of the STAT1 transcription factor. However, the contribution of tonic levels of IFN to immune homeostasis in the absence of acute infection remains largely unexplored. We report that STAT1 KO mice spontaneously developed an inflammatory disease marked by myeloid hyperplasia and splenic accumulation of hematopoietic stem cells. Moreover, these animals developed inflammatory bowel disease. Profiling gut bacteria revealed a profound dysbiosis in the absence of tonic IFN signaling, which triggered expansion of T_H17 cells and loss of splenic T_reg cells. Reduction of bacterial load by antibiotic treatment averted the T_H17 bias and blocking IL17 signaling prevented myeloid expansion and splenic stem cell accumulation. Thus, tonic IFNs regulate gut microbial ecology, which is crucial for maintaining physiologic immune homeostasis and preventing inflammation.

Network Pharmacology-Based Investigation of the System-Level Molecular Mechanisms of the Hematopoietic Activity of Samul-Tang, a Traditional Korean Herbal Formula

Hematopoiesis is a dynamic process of the continuous production of diverse blood cell types to meet the body's physiological demands and involves complex regulation of multiple cellular mechanisms in hematopoietic stem cells, including proliferation, self-renewal, differentiation, and apoptosis. Disruption of the hematopoietic system is known to cause various hematological disorders such as myelosuppression. There is growing evidence on the beneficial effects of herbal medicines on hematopoiesis; however, their mechanism of action remains unclear. In this study, we conducted a network pharmacological-based investigation of the system-level mechanisms underlying the hematopoietic activity of Samul-tang, which is an herbal formula consisting of four herbal medicines, including Angelicae Gigantis Radix, Rehmanniae Radix Preparata, Paeoniae Radix Alba, and Cnidii Rhizoma. In silico analysis of the absorption-distribution-metabolism-excretion model identified 16 active phytochemical compounds contained in Samul-tang that may target 158 genes/proteins associated with myelosuppression to exert pharmacological effects. Functional enrichment analysis suggested that the targets of Samul-tang were significantly enriched in multiple pathways closely related to the hematopoiesis and myelosuppression development, including the PI3K-Akt, MAPK, IL-17, TNF, FoxO, HIF-1, NF-kappa B, and p53 signaling pathways. Our study provides novel evidence regarding the system-level mechanisms underlying the hematopoiesis-promoting effect of herbal medicines for hematological disorder treatment.

When worlds collide: Th17 and Treg cells in cancer and autoimmunity

The balance between Th17 cells and regulatory T cells (Tregs) has emerged as a prominent factor in regulating autoimmunity and cancer. Th17 cells are vital for host defense against pathogens but have also been implicated in causing autoimmune disorders and cancer, though their role in carcinogenesis is less well understood. Tregs are required for self-tolerance and defense against autoimmunity and often correlate with cancer progression. This review addresses the importance of a functional homeostasis between these two subsets in health and the consequences of its disruption when these forces collide in disease. Importantly, we discuss the ability of Th17 cells to mediate cancer regression in immunotherapy, including adoptive transfer and checkpoint blockade therapy, and the therapeutic possibilities of purposefully offsetting the Th17/Treg balance to treat patients with cancer as well as those with autoimmune diseases.

In vitro stimulatory effect of N-acetyl tryptophan-glucopyranoside against gamma radiation induced immunosuppression

Radiation-induced manifestations like free radical burst, oxidative damage and apoptosis leading to cell death. In present study, N-acetyl tryptophan glucopyranoside (NATG) was assessed for its immune-radioprotective activities using J774A.1 cells. Clonogenic cell survival, cell cycle progression and cytokines i.e. IFN-γ, TNF-α, IL-2, IL-10, IL-12, IL-13 and IL-17A expression were evaluated in irradiated and NATG pretreated cells using clonogenic formation ability, flow cytometry and ELISA assay. Results indicated that 0.25μg/ml NATG exhibited maximum radioprotection against gamma-radiation (2Gy) without intervening in cell cycle progression. NATG pretreated (-2 h) plus irradiated cells showed significant elevation in IFN-γ (∼38.2%), IL-17A (∼53.7%) and IL-12 (∼58.8%) expression as compared to only irradiated cells. Conversely, significant decrease in TNF-α (∼21.6%), IL-10 (∼31.2%), IL-2 (∼23.7%) and IL-13 expression (∼17.8%) were observed in NATG pretreated plus irradiated cells as compared to irradiated cells. Conclusively, NATG pretreatment to irradiated J774A.1 cells, stimulate Th₁ while diminish Th₂ cytokines that contributes to radioprotection.

Bone Marrow-Derived Mesenchymal Stromal Cells from Patients with Sickle Cell Disease Display Intact Functionality

Hematopoietic cell transplantation (HCT) is the only cure for sickle cell disease (SCD), but engraftment remains challenging in patients lacking matched donors. Infusion of mesenchymal stromal cells (MSCs) at the time of HCT may promote hematopoiesis and ameliorate graft-versus-host disease. Experimental murine models suggest MSC major histocompatibility complex compatibility with recipient impacts their in vivo function, suggesting autologous MSCs could be superior to third-party MSCs for promoting HCT engraftment. Here we tested whether bone marrow (BM)-derived MSCs from SCD subjects have comparable functionality compared with MSCs from healthy volunteers. SCD MSC doubling time and surface marker phenotype did not differ significantly from non-SCD. Third-party and autologous (SCD) T cell proliferation was suppressed in a dose-dependent manner by all MSCs. SCD MSCs comparably expressed indoleamine-2,3-dioxygenase, which based on transwell and blocking experiments appeared to be the dominant immunomodulatory pathway. The expression of key genes involved in hematopoietic stem cell (HSC)-MSC interactions was minimally altered between SCD and non-SCD MSCs. Expression was, however, altered by IFN-γ stimulation, particularly CXCL14, CXCL26, CX3CL1, CKITL, and JAG1, indicating the potential to augment MSC expression by cytokine stimulation. These data demonstrate the feasibility of expanding BM-derived MSCs from SCD patients that phenotypically and functionally do not differ per International Society of Cell Therapy essential criteria from non-SCD MSCs, supporting initial evaluation (primarily for safety) of autologous MSCs to enhance haploidentical HSC engraftment in SCD.

Interleukin-17 and its implication in the regulation of differentiation and function of hematopoietic and mesenchymal stem cells

Adult stem cells have a great potential applicability in regenerative medicine and cell-based therapies. However, there are still many unresolved issues concerning their biology, and the influence of the local microenvironment on properties of stem cells has been increasingly recognized. Interleukin (IL-) 17, as a cytokine implicated in many physiological and pathological processes, should be taken into consideration as a part of a regulatory network governing tissue-associated stem cells' fate. This review is focusing on the published data on the effects of IL-17 on the properties and function of hematopoietic and mesenchymal stem cells and trying to discuss that IL-17 achieves many of its roles by acting on adult stem cells.

Aplotaxene blocks T cell activation by modulation of protein kinase C-θ-dependent pathway

Aplotaxene, (8Z, 11Z, 14Z)-heptadeca-1, 8, 11, 14-tetraene, is one of the major components of essential oil obtained from Inula helenium root, which is used in Oriental medicine. However, the effects of aplotaxene on immunity have not been investigated. Here, we show that aplotaxene inhibits T cell activation in terms of IL-2 and CD69 expression. Aplotaxene, at a concentration that optimally inhibits IL-2 production, has little effect on apoptotic or necrotic cell death, suggesting that apoptosis is not a mechanism for aplotaxene-mediated inhibition of T cell activation. Aplotaxene affects neither superantigeninduced conjugate formation between Jurkat T cells and Raji B cells nor clustering of CD3 and LFA-1 at the immunological synapse. Aplotaxene significantly inhibits PKC-θ phosphorylation and translocation to the immunological synapse, and blocks PMA-induced T-cell receptor internalization. Furthermore, aplotaxene leads to inhibition of mitogen-activated protein kinases (JNK, ERK and p38) phosphorylation and NF-κB, NF-AT, and AP-1 promoter activities in Jurkat T cells. Taken together, our findings provide evidence for the immunosuppressive effect of aplotaxene on activated T cells through the modulation of the PKC-θ and MAPK pathways, suggesting that aplotaxene may be a novel immunotherapeutic agent for immunological diseases related to the overactivation of T cells.

Essentials of Th17 cell commitment and plasticity

CD4(+) T helper (Th) cells exist in a variety of epigenetic states that determine their function, phenotype, and capacity for persistence. These polarization states include Th1, Th2, Th17, and Foxp3(+) T regulatory cells, as well as the more recently described T follicular helper, Th9, and Th22 cells. Th17 cells express the master transcriptional regulator retinoic acid-related orphan receptor γ thymus and produce canonical interleukin (IL)-17A and IL-17F cytokines. Th17 cells display a great degree of context-dependent plasticity, as they are capable of acquiring functional characteristics of Th1 cells. This late plasticity may contribute to the protection against microbes, plays a role in the development of autoimmunity, and is necessary for antitumor activity of Th17 cells in adoptive cell transfer therapy models. Moreover, plasticity of this subset is associated with higher in vivo survival and self-renewal capacity and less senescence than Th1 polarized cells, which have less plasticity and more phenotypic stability. New findings indicate that subset polarization of CD4(+) T cells not only induces characteristic patterns of surface markers and cytokine production but also has a maturational aspect that affects a cell's ability to survive, respond to secondary stimulation, and form long-term immune memory.

Elevating body temperature enhances hematopoiesis and neutrophil recovery after total body irradiation in an IL-1-, IL-17-, and G-CSF-dependent manner

Neutropenia is a common side effect of cytotoxic chemotherapy and radiation, increasing the risk of infection in these patients. Here we examined the impact of body temperature on neutrophil recovery in the blood and bone marrow after total body irradiation (TBI). Mice were exposed to either 3 or 6 Gy TBI followed by a mild heat treatment that temporarily raised core body temperature to approximately 39.5°C. Neutrophil recovery was then compared with control mice that received either TBI alone heat treatment alone. Mice that received both TBI and heat treatment exhibited a significant increase in the rate of neutrophil recovery in the blood and an increase in the number of marrow hematopoietic stem cells and neutrophil progenitors compared with that seen in mice that received either TBI or heat alone. The combination treatment also increased G-CSF concentrations in the serum, bone marrow, and intestinal tissue and IL-17, IL-1β, and IL-1α concentrations in the intestinal tissue after TBI. Neutralizing G-CSF or inhibiting IL-17 or IL-1 signaling significantly blocked the thermally mediated increase in neutrophil numbers. These findings suggest that a physiologically relevant increase in body temperature can accelerate recovery from neutropenia after TBI through a G-CSF-, IL-17-, and IL-1-dependent mechanism.

A bioinformatics filtering strategy for identifying radiation response biomarker candidates

The number of biomarker candidates is often much larger than the number of clinical patient data points available, which motivates the use of a rational candidate variable filtering methodology. The goal of this paper is to apply such a bioinformatics filtering process to isolate a modest number (<10) of key interacting genes and their associated single nucleotide polymorphisms involved in radiation response, and to ultimately serve as a basis for using clinical datasets to identify new biomarkers. In step 1, we surveyed the literature on genetic and protein correlates to radiation response, in vivo or in vitro, across cellular, animal, and human studies. In step 2, we analyzed two publicly available microarray datasets and identified genes in which mRNA expression changed in response to radiation. Combining results from Step 1 and Step 2, we identified 20 genes that were common to all three sources. As a final step, a curated database of protein interactions was used to generate the most statistically reliable protein interaction network among any subset of the 20 genes resulting from Steps 1 and 2, resulting in identification of a small, tightly interacting network with 7 out of 20 input genes. We further ranked the genes in terms of likely importance, based on their location within the network using a graph-based scoring function. The resulting core interacting network provides an attractive set of genes likely to be important to radiation response.

The dysregulation of cytokine networks in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is an autoimmune disease associated with chronic immune activation and tissue damage. Organ damage in SLE results from the deposition of immune complexes and the infiltration of activated T cells into susceptible organs. Cytokines are intimately involved in every step of the SLE pathogenesis. Defective immune regulation and uncontrolled lymphocyte activation, as well as increased antigen presenting cell maturation are all influenced by cytokines. Moreover, expansion of local immune responses as well as tissue infiltration by pathogenic cells is instigated by cytokines. In this review, we describe the main cytokine abnormalities reported in SLE and discuss the mechanisms that drive their aberrant production as well as the pathogenic pathways that their presence promotes.

Effects of chimerism on the mice heart transplanted survival with the bone marrow infusion

AIMS

To evaluate the effects of chimerism on the mice heart transplanted survival with the bone marrow infusion.

METHODS

Bone marrow cells (BMCs) were obtained from BALB/c mice. These BMCs were injected into the irradiated (2Gy-Co60) C57BL/6 mice through femoral vein. Then Group A mice were treated with Cyclosporine (1mg/kg) for 21days and Group B were not treated with Cyclosporine. Group C were treated as the control group without BMCs infusion. Group D were treated with Cyclosporine (1mg/kg) for 21days pre-hearttransplantation without BMCs infusion. After 21days, the C57BL/6 mice received heart allografts from BALB/c. To determine the degree of chimerism in BMCs infusion recipients, peripheral blood were isolated on day 7, 14, 21. Allografts were harvested 10days after heart transplantation for the histological analysis.

RESULTS

(1) Chimerism detected in the peripheral blood of Group A mice on day 7 after BMCs infusion was 6.1±2.5%, on day 14 was 15.4±2.9% and on day 21 was 10.7±2.6%. For the Group B mice on day 7 after BMCs infusion, the chimerism was 2.8±1.1%, on day 14 was 11.2±4.8% and on day 21 was 7.4±3.7%. For the Groups C and D mice, no chimerism was observed. Group A mice had the tendency toward improved level of chimerism than Group B mice. (2) The survival time of Group A (n=6) was 13.0±1.4days which was significantly longer than Group B (n=6) with the survival time was 8.5±1.3days (p<0.001), also longer than the mice in Groups C and D, the survival time of which were 10.0±1.3days (p=0.008) and 9.4±1.1days (p=0.004). There is no significant difference among Groups B, C, and D. (3) The HE staining showed the much more seriously heart rejection in Groups B, C and D than Group A.

CONCLUSIONS

The chimerism was found in the BMCs infusion groups. Without the CsA treatment combined with chimerism could not protect the transplanted heart. There was no obvious evidence showed that the chimerism alone could improve the survival time of cardiac allografts in mice.

Genetics and genomics of radiotherapy toxicity: towards prediction

Radiotherapy is involved in many curative treatments of cancer; millions of survivors live with the consequences of treatment, and toxicity in a minority limits the radiation doses that can be safely prescribed to the majority. Radiogenomics is the whole genome application of radiogenetics, which studies the influence of genetic variation on radiation response. Work in the area focuses on uncovering the underlying genetic causes of individual variation in sensitivity to radiation, which is important for effective, safe treatment. In this review, we highlight recent advances in radiotherapy and discuss results from four genome-wide studies of radiotoxicity.

Interleukins, from 1 to 37, and interferon-γ: receptors, functions, and roles in diseases

Advancing our understanding of mechanisms of immune regulation in allergy, asthma, autoimmune diseases, tumor development, organ transplantation, and chronic infections could lead to effective and targeted therapies. Subsets of immune and inflammatory cells interact via ILs and IFNs; reciprocal regulation and counter balance among T(h) and regulatory T cells, as well as subsets of B cells, offer opportunities for immune interventions. Here, we review current knowledge about ILs 1 to 37 and IFN-γ. Our understanding of the effects of ILs has greatly increased since the discoveries of monocyte IL (called IL-1) and lymphocyte IL (called IL-2); more than 40 cytokines are now designated as ILs. Studies of transgenic or knockout mice with altered expression of these cytokines or their receptors and analyses of mutations and polymorphisms in human genes that encode these products have provided important information about IL and IFN functions. We discuss their signaling pathways, cellular sources, targets, roles in immune regulation and cellular networks, roles in allergy and asthma, and roles in defense against infections.

Mechanisms controlling Th17 cytokine expression and host defense

Th17 cells contribute to mucosal immunity by stimulating epithelial cells to induce antimicrobial peptides, granulopoiesis, neutrophil recruitment, and tissue repair. Recent studies have identified important roles for commensal microbiota and Ahr ligands in stabilizing Th17 gene expression in vivo, linking environmental cues to CD4 T cell polarization. Epigenetic changes that occur during the transition from naïve to effector Th17 cells increase the accessibility of il17a, il17f, and il22 loci to transcription factors. In addition, Th17 cells maintain the potential for expressing T-bet, Foxp3, or GATA-binding protein-3, explaining their plastic nature under various cytokine microenvironments. Although CD4 T cells are major sources of IL-17 and IL-22, innate cell populations, including γδ T cells, NK cells, and lymphoid tissue-inducer cells, are early sources of these cytokines during IL-23-driven responses. Epithelial cells and fibroblasts are important cellular targets for IL-17 in vivo; however, recent data suggest that macrophages and B cells are also stimulated directly by IL-17. Thus, Th17 cells interact with multiple populations to facilitate protection against intracellular and extracellular pathogens.

Vaccine-induced protection against 3 systemic mycoses endemic to North America requires Th17 cells in mice

Worldwide rates of systemic fungal infections, including three of the major pathogens responsible for such infections in North America (Coccidioides posadasii, Histoplasma capsulatum, and Blastomyces dermatitidis), have soared recently, spurring interest in developing vaccines. The development of Th1 cells is believed to be crucial for protective immunity against pathogenic fungi, whereas the role of Th17 cells is vigorously debated. In models of primary fungal infection, some studies have shown that Th17 cells mediate resistance, while others have shown that they promote disease pathology. Here, we have shown that Th1 immunity is dispensable and that fungus-specific Th17 cells are sufficient for vaccine-induced protection against lethal pulmonary infection with B. dermatitidis in mice. Further, vaccine-induced Th17 cells were necessary and sufficient to protect against the three major systemic mycoses in North America. Mechanistically, Th17 cells engendered protection by recruiting and activating neutrophils and macrophages to the alveolar space, while the induction of Th17 cells and acquisition of vaccine immunity unexpectedly required the adapter molecule Myd88 but not the fungal pathogen recognition receptor Dectin-1. These data suggest that human vaccines against systemic fungal infections should be designed to induce Th17 cells if they are to be effective.

Role of TH-17 cells in rheumatic and other autoimmune diseases

In humans multiple pathways can induce TH-17 cell differentiation, whereas in mice this process is mostly modulated by IL-6 and TGF-β. IL-17 produced by TH-17 cells has been associated with a number of inflammatory autoimmune diseases including psoriasis, systemic lupus erythematosus, inflammatory bowel disease, multiple sclerosis, and rheumatoid arthritis. In this review, we have primarily focused on the role of TH-17 cells/IL-17 in the pathogenesis of rheumatoid arthritis and experimental arthritis. The potential role of TH-17 cells in rheumatoid arthritis progression has been demonstrated by correlating the percent TH-17 cells or levels of IL-17 with rheumatoid arthritis disease activity score and C-reactive protein levels. Further, previous studies suggest that IL-17 mediated vascularization may lay the foundation for rheumatoid arthritis joint neutrophil and monocyte recruitment as well as cartilage and bone destruction. The profound role of IL-17 in the pathogenesis of experimental arthritis may be due to its synergistic effect with TNF-α and IL-1β. Although the initial clinical trial employing anti-IL-17 antibody has been promising for rheumatoid arthritis, future studies in humans will shed more light on how anti-IL-17 therapy affects rheumatoid arthritis and other autoimmune disease pathogenesis.

Combined effect of IL-17 and blockade of nitric oxide biosynthesis on haematopoiesis in mice

AIM

The study was undertaken to extend our investigation concerning both the in vivo activity of interleukin (IL)-17 and the specific role of nitric oxide (NO) in IL-17-induced effects in the process of haematopoiesis.

METHODS

CBA mice were simultaneously treated with IL-17 and/or nitric oxide synthase (NOS) inhibitor, l-NAME, for 5 days and changes within various haematopoietic cell lineages in bone marrow, spleen and peripheral blood were analysed.

RESULTS

Findings showed that administration of both IL-17 and l-NAME stimulated increase in net haematopoiesis in normal mice. IL-17-enhanced myelopoiesis was characterized by stimulation of both femoral and splenic haematopoietic progenitor cells and morphologically recognizable granulocytes. Additionally, IL-17 induced alterations in the frequency of erythroid progenitor cells in both bone marrow and spleen, accompanied with their mobilization to the peripheral blood. As a consequence of these changes in the erythroid cell compartments, significant reticulocytosis was observed, which evidenced that in IL-17-treated mice effective erythropoiesis occurred. Exposure of mice to NOS inhibitor also increased the number of both granulocyte-macrophage and erythroid progenitors in bone marrow and spleens, and these alterations were followed by the mobilization of erythroid progenitors and elevated content of reticulocytes in peripheral blood. The specific role of NO in IL-17-induced haematopoiesis was demonstrated only in the IL-17-reducing effect on bone marrow late stage erythroid progenitors, CFU-E.

CONCLUSION

The results demonstrated the involvement of both IL-17 and NO in the regulation of haematopoietic cell activity in various haematopoietic compartments. They further suggest that IL-17 effects are differentially mediated depending on the haematopoietic microenvironments.

Mycophenolic acid suppresses granulopoiesis by inhibition of interleukin-17 production

Mycophenolic acid is a commonly used immunosuppressant after organ transplantation and in autoimmune diseases; however, myelosuppression is a major complication despite its largely favorable side-effect profile. Mycophenolic acid targets inosine monophosphate dehydrogenase, which is essential for T-cell proliferation. The T-cell cytokine interleukin-17 (IL-17 or IL-17A) and its receptor maintain normal neutrophilic granulocyte numbers in mice by induction of granulocyte-colony-stimulating factor. To test whether mycophenolic acid induces neutropenia by inhibiting IL-17-producing T cells, we treated C57Bl/6 mice with mycophenolate-mofetil (the orally available pro-drug) and found a dose-dependent decrease in blood neutrophils. This myelosuppressive effect was completely abolished in mice that lack the IL-17 receptor. Mycophenolic acid delayed myeloid recovery after bone marrow transplantation and decreased the percentage of IL-17-producing T cells in the spleen and thymus, and inhibited IL-17 production in human and mouse T cells in vitro. Injection of IL-17 during mycophenolic acid treatment overcame the suppression of the circulating neutrophil levels. Our study shows that mycophenolic acid suppresses neutrophil production by inhibiting IL-17 expression, suggesting that measurement of this interleukin might be useful in estimating the risk of neutropenia in clinical settings.

Effector mechanisms of interleukin-17 in collagen-induced arthritis in the absence of interferon-gamma and counteraction by interferon-gamma

INTRODUCTION

Interleukin (IL)-17 is a pro-inflammatory cytokine in rheumatoid arthritis (RA) and collagen-induced arthritis (CIA). Since interferon (IFN)-gamma inhibits Th17 cell development, IFN-gamma receptor knockout (IFN-gammaR KO) mice develop CIA more readily. We took advantage of this model to analyse the mechanisms of action of IL-17 in arthritis. The role of IFN-gamma on the effector mechanisms of IL-17 in an in vitro system was also investigated.

METHODS

IFN-gammaR KO mice induced for CIA were treated with anti-IL-17 or control antibody. The collagen type II (CII)-specific humoral and cellular autoimmune responses, myelopoiesis, osteoclastogenesis, and systemic cytokine production were determined. Mouse embryo fibroblasts (MEF) were stimulated with IL-17, tumor necrosis factor (TNF)-alpha and the expression of cytokines and chemokines were determined.

RESULTS

A preventive anti-IL-17 antibody treatment inhibited CIA in IFNgammaR KO mice. In the joints of anti-IL-17-treated mice, neutrophil influx and bone destruction were absent. Treatment reduced the cellular autoimmune response as well as the splenic expansion of CD11b+ cells, and production of myelopoietic cytokines such as granulocyte macrophage colony-stimulating factor (GM-CSF) and IL-6. IL-17 and TNF-alpha synergistically induced granulocyte chemotactic protein-2 (GCP-2), IL-6 and receptor activator of NFkappaB ligand (RANKL) in MEF. This induction was profoundly inhibited by IFN-gamma in a STAT-1 (signal transducer and activator of transcription-1)-dependent way.

CONCLUSIONS

In the absence of IFN-gamma, IL-17 mediates its pro-inflammatory effects mainly through stimulatory effects on granulopoiesis, neutrophil infiltration and bone destruction. In vitro IFN-gamma profoundly inhibits the effector function of IL-17. Thus, aside from the well-known inhibition of the development of Th17 cells by IFN-gamma, this may be an additional mechanism through which IFN-gamma attenuates autoimmune diseases.

IL-17A controls IL-17F production and maintains blood neutrophil counts in mice

G-CSF, its receptor, and IL-17 receptor A (IL-17RA) are all required to maintain baseline neutrophil counts in mice. In this study, we tested whether IL-17F could compensate and maintain baseline neutrophil counts in the absence of IL-17A. Unlike the reduced neutrophil counts found in IL-17RA-deficient mice, neutrophil counts were mildly increased in IL-17A-deficient (Il17a(-/-)) animals. There was no evidence for infection or altered neutrophil function. Plasma G-CSF and IL-17F levels were elevated in Il17a(-/-) compared with wild-type mice. IL-17F was mainly produced in the spleen and mesenteric lymph nodes, but IL-23 was unaltered in Il17a(-/-) mice. Instead, Il17a(-/-) splenocytes differentiated with IL-6, TGF-beta, and IL-23 ex vivo produced significantly more IL-17F in response to IL-23 than wild-type cells. Adding rIL-17A to Il17a(-/-) splenocyte cultures reduced IL-17F mRNA and protein secretion. These effects were also observed in wild-type but not IL-17RA-deficient cells. We conclude that IL-17A mediated suppression of IL-17F production and secretion requires IL-17RA and is relevant to maintain the normal set point of blood neutrophil counts in vivo.

Molecular explanation for the contradiction between systemic Th17 defect and localized bacterial infection in hyper-IgE syndrome

Hyper-IgE syndrome (HIES) is a primary immunodeficiency characterized by atopic manifestations and susceptibility to infections with extracellular pathogens, typically Staphylococcus aureus, which preferentially affect the skin and lung. Previous studies reported the defective differentiation of T helper 17 (Th17) cells in HIES patients caused by hypomorphic STAT3 mutations. However, the apparent contradiction between the systemic Th17 deficiency and the skin/lung-restricted susceptibility to staphylococcal infections remains puzzling. We present a possible molecular explanation for this enigmatic contradiction. HIES T cells showed impaired production of Th17 cytokines but normal production of classical proinflammatory cytokines including interleukin 1β. Normal human keratinocytes and bronchial epithelial cells were deeply dependent on the synergistic action of Th17 cytokines and classical proinflammatory cytokines for their production of antistaphylococcal factors, including neutrophil-recruiting chemokines and antimicrobial peptides. In contrast, other cell types were efficiently stimulated with the classical proinflammatory cytokines alone to produce such factors. Accordingly, keratinocytes and bronchial epithelial cells, unlike other cell types, failed to produce antistaphylococcal factors in response to HIES T cell–derived cytokines. These results appear to explain, at least in part, why HIES patients suffer from recurrent staphylococcal infections confined to the skin and lung in contrast to more systemic infections in neutrophil-deficient patients.

Breaking old paradigms: Th17 cells in autoimmune arthritis

Aberrant helper T cell activation has been implicated in the pathogenesis of an array of autoimmune diseases. In this review, we summarize evidence that suggests the involvement of a novel T cell subset, the Th17 lineage, in rheumatoid arthritis. In particular, we focus on the role of Th17 cells in inducing and perpetuating the chronic inflammation, cartilage damage, and bone erosion that are hallmark phases of joint destruction and consider current and emerging therapies that seek to disrupt the inflammatory Th17 network and shift the immune system back towards homeostasis.

IL-17 and Th17 Cells

CD4+ T cells, upon activation and expansion, develop into different T helper cell subsets with different cytokine profiles and distinct effector functions. Until recently, T cells were divided into Th1 or Th2 cells, depending on the cytokines they produce. A third subset of IL-17-producing effector T helper cells, called Th17 cells, has now been discovered and characterized. Here, we summarize the current information on the differentiation and effector functions of the Th17 lineage. Th17 cells produce IL-17, IL-17F, and IL-22, thereby inducing a massive tissue reaction owing to the broad distribution of the IL-17 and IL-22 receptors. Th17 cells also secrete IL-21 to communicate with the cells of the immune system. The differentiation factors (TGF-β plus IL-6 or IL-21), the growth and stabilization factor (IL-23), and the transcription factors (STAT3, RORγt, and RORα) involved in the development of Th17 cells have just been identified. The participation of TGF-β in the differentiation of Th17 cells places the Th17 lineage in close relationship with CD4+CD25+Foxp3+ regulatory T cells (Tregs), as TGF-β also induces differentiation of naive T cells into Foxp3+ Tregs in the peripheral immune compartment. The investigation of the differentiation, effector function, and regulation of Th17 cells has opened up a new framework for understanding T cell differentiation. Furthermore, we now appreciate the importance of Th17 cells in clearing pathogens during host defense reactions and in inducing tissue inflammation in autoimmune disease.

IL-17 and Th17 Cells

CD4+ T cells, upon activation and expansion, develop into different T helper cell subsets with different cytokine profiles and distinct effector functions. Until recently, T cells were divided into Th1 or Th2 cells, depending on the cytokines they produce. A third subset of IL-17-producing effector T helper cells, called Th17 cells, has now been discovered and characterized. Here, we summarize the current information on the differentiation and effector functions of the Th17 lineage. Th17 cells produce IL-17, IL-17F, and IL-22, thereby inducing a massive tissue reaction owing to the broad distribution of the IL-17 and IL-22 receptors. Th17 cells also secrete IL-21 to communicate with the cells of the immune system. The differentiation factors (TGF-beta plus IL-6 or IL-21), the growth and stabilization factor (IL-23), and the transcription factors (STAT3, RORgammat, and RORalpha) involved in the development of Th17 cells have just been identified. The participation of TGF-beta in the differentiation of Th17 cells places the Th17 lineage in close relationship with CD4+CD25+Foxp3+ regulatory T cells (Tregs), as TGF-beta also induces differentiation of naive T cells into Foxp3+ Tregs in the peripheral immune compartment. The investigation of the differentiation, effector function, and regulation of Th17 cells has opened up a new framework for understanding T cell differentiation. Furthermore, we now appreciate the importance of Th17 cells in clearing pathogens during host defense reactions and in inducing tissue inflammation in autoimmune disease.

IL-17F/IL-17R interaction stimulates granulopoiesis in mice

OBJECTIVE

IL-17F, a member of the interleukin (IL)-17 cytokine family, most closely resembles IL-17A structurally. IL-17A is a potent stimulator of granulopoiesis; its expression is induced in response to microbial challenge. Although IL-17F is considered to be a weak IL-17A analog that is also mediating its effect via IL-17R, its exact role and in vivo functions are unknown. Our goal was to determine the in vivo activity of IL-17F on granulopoiesis as well as on release of granulopoiesis-stimulating downstream cytokines in mice and directly compare its effect to IL-17A.

MATERIALS AND METHODS

Murine IL-17A (mIL-17A) or IL-17F (mIL-17F) was expressed in vivo in C57BL6 mice using adenoviral gene transfer technology. Peripheral cell counts were assessed as well as hematopoietic precursors using colony-forming assays at set time points. Downstream cytokines were measured using enzyme-linked immunosorbent assay and reverse transcriptase polymerase chain reaction.

RESULTS

We found mIL-17F to have similar expression kinetics as mIL-17A in splenocytes in vitro and in vivo, following challenge with microbial agents. Overexpression of mIL-17F in vivo resulted in similar neutrophilia and only in slightly reduced myeloid progenitor expansion when compared to mIL-17A. In vivo, there was no difference in releases for granulocyte-macrophage colony-stimulating factor; regulated on activation, normal T expressed and secreted; interferon-inducible protein-10; IL-6; and monocyte chemotactic protein-1 between either cytokine. IL-1A, macrophage inflammatory protein -2 (MIP), KC, and granulocyte colony-stimulating factor expression was approximately half of that seen with mIL-17A.

CONCLUSION

Both IL-17A and IL-17F are induced by similar stimuli, have similar expression kinetics and despite only minimal in vitro activity for IL-17F, surprisingly they exert similar in vivo bioactivity. IL-17F bioactivity appears to be augmented in vivo through mechanisms that require further investigation.

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.

A selective phosphodiesterase 4 (PDE4) inhibitor Zl-n-91 suppresses IL-17 production by human memory Th17 cells

Th17 cells are highly proinflammatory and involved in the immunopathogenesis of severe autoimmune diseases. Selective phosphodiesterase 4 (PDE4) inhibitors, which elevate intracellular cAMP by inhibiting the hydrolysis of cAMP, have been demonstrated to be an effective anti-inflammatory agent in airway inflammatory diseases. In the present study, we assessed the effect of a selective PDE4 inhibitor Zl-n-91 on IL-17 production by PBMCs and by purified CD4(+) T cells following stimulation. The results for the first time demonstrated that the addition of Zl-n-91 into cell cultures of PBMCs and purified CD4(+) T cells could result in the suppression of IL-17 production at the protein and mRNA levels. Further analysis indicated that Zl-n-91 had a direct inhibitory effect on the IL-17 production by memory Th17 cells via the suppression of activation, proliferation and division of CD4(+) T cells. Our data suggested that Zl-n-91 might have beneficial effects in the treatment of IL-17-related autoimmune diseases.

The biological functions of T helper 17 cell effector cytokines in inflammation

T helper 17 (Th17) cells belong to a recently identified T helper subset, in addition to the traditional Th1 and Th2 subsets. These cells are characterized as preferential producers of interleukin-17A (IL-17A), IL-17F, IL-21, and IL-22. Th17 cells and their effector cytokines mediate host defensive mechanisms to various infections, especially extracellular bacteria infections, and are involved in the pathogenesis of many autoimmune diseases. The receptors for IL-17 and IL-22 are broadly expressed on various epithelial tissues. The effector cytokines of Th17 cells, therefore, mediate the crucial crosstalk between immune system and tissues, and play indispensable roles in tissue immunity.

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.

Umbilical cord blood xenografts in immunodeficient mice reveal that T cells enhance hematopoietic engraftment beyond overcoming immune barriers by stimulating stem cell differentiation

Clinical experience and animal models have shown that donor T cell depletion (TCD) adversely affects engraftment of hematopoietic stem cells (HSCs). Although it is known that donor T cells are acting to overcome residual host immune barriers, they may also exert effects independent of host resistance via direct or indirect interactions with donor stem cells, their microenvironment, or key differentiation events. To more precisely define the effect of T cells on engraftment, we have performed human umbilical cord blood (UCB) transplantation into immunodeficient mice under limiting dilution conditions. UCB mononuclear cells (MNC) or TCD UCB were transplanted into NOD/LtSz-scid/scid B2m(null) (NOD/SCID-beta(2)m(-/-)) mice. Cohorts of mice received UCB MNC or TCD UCB at 5 dose levels between 5 x 10(4) and 5 x 10(6) cells. At dose levels at or above 10(5) cells, engraftment was higher in the MNC recipients (n = 32) than the TCD recipients (n = 31) in a dose-dependent manner. Despite this difference, limiting dilution analysis to determine functional stem cell frequency revealed that SCID repopulating cells in TCD UCB was not significantly less than in CB MNCs, suggesting that T cells may facilitate engraftment at stages beyond the stem cell. Add-back of CD3/CD28 costimulated T cells restored and appeared to enhance engraftment, both in NOD/SCID-beta(2)m(-/-) as well as NOD/LtSz-scid IL2Rgamma(null) (NOG) recipients. These results, in a model where there are minimal host immune barriers to overcome, suggest T cells possess additional graft-facilitating properties. CD3/CD28 costimulation of UCB T cells represents a potential strategy for enhancing the engraftment of UCB.

Th17 cells and mucosal host defense

Th17 cells are a new lineage of T-cells that are controlled by the transcription factor RORgammat and develop independent of GATA-3, T-bet, Stat 4 and Stat 6. Novel effector molecules produced by these cells include IL-17A, IL-17F, IL-22, and IL-26. IL-17RA binds IL-17A and IL-17F and is critical for host defense against extracellular planktonic bacteria by regulating chemokine gradients for neutrophil emigration into infected tissue sites as well as host granulopoiesis. Moreover, IL-17 and IL-22 regulate the production of antimicrobial proteins in mucosal epithelium. Although TGF-beta1 and IL-6 have been shown to be critical for development of Th17 cells from naive precursors, IL-23 is also important in regulating IL-17 release in mucosal tissues in response to infectious stimuli. Compared to Th1 cells, IL-23 and IL-17 show limited roles in controlling host defense against primary infections with intracellular bacteria such as Mycobacterium tuberculosis suggesting a predominate role of the Th17 lineage in host defense against extracellular pathogens. However, in the setting of chronic biofilm infections, as that occurs with cystic fibrosis or bronchiectasis, Th17 cells may be key contributors of tissue injury.

Th17 cell induction and immune regulatory effects

The T help 1 (Th1) and Th2 cell classification have 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, which 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. In this review, we will focus on recent studies that have identified new subsets of Th cells, new insights regarding the induced generation and differentiation mechanisms of Th17 cells and immune regulatory effects.