IL-17A-producing gammadelta T and Th17 lymphocytes mediate lung inflammation but not fibrosis in experimental silicosis

siRNA-Act1 inhibits the function of IL-17 on lung fibroblasts via the NF-κB pathway

BACKGROUND

Interleukin (IL)-17-producing T lymphocytes play a role in pulmonary fibrosis, but the possible mechanism of IL-17 on lung fibroblasts remains uncertain.

OBJECTIVES

To explore the role and possible mechanism of IL-17 on lung fibroblasts.

METHODS

A mouse model of pulmonary fibrosis was established by intratracheal administration of 5 mg/kg bleomycin. At 14 days following bleomycin administration the pulmonary fibroblasts were isolated, cultured and identified. siRNA for activator 1 (Act1) were transfected into lung fibroblasts, which were cocultured with IL-17. The NF-κB pathway was detected for IL-17 on the lung fibroblasts.

RESULTS

IL-17R was increased significantly at 14 days in the bleomycin-induced pulmonary fibroblast model, exogenous IL-17 significantly promoted the proliferation of the pulmonary fibroblasts in primary culture and obviously increased the expression of α-smooth muscle actin and type I and type III collagen in the fibroblasts. We found that IL-17 rapidly activated the NF-κB signaling pathway through activated phosphorylated p65 and IκB, and all roles of IL-17 on lung fibroblasts were inhibited under the interference for the expression of Act1 in lung fibroblasts.

CONCLUSION

IL-17 may directly promote the proliferation, transformation and collagen synthesis of lung fibroblasts via the NF-kB signaling pathway, which can be inhibited by the interference for the expression of Act1.

Requirements for innate immune pathways in environmentally induced autoimmunity

There is substantial evidence that environmental triggers in combination with genetic and stochastic factors play an important role in spontaneous autoimmune disease. Although the specific environmental agents and how they promote autoimmunity remain largely unknown, in part because of diverse etiologies, environmentally induced autoimmune models can provide insights into potential mechanisms. Studies of idiopathic and environmentally induced systemic autoimmunity show that they are mediated by common adaptive immune response genes. By contrast, although the innate immune system is indispensable for autoimmunity, there are clear differences in the molecular and cellular innate components that mediate specific systemic autoimmune diseases, suggesting distinct autoimmune-promoting pathways. Some of these differences may be related to the bifurcation of toll-like receptor signaling that distinguishes interferon regulatory factor 7-mediated type I interferon production from nuclear factor-κB-driven proinflammatory cytokine expression. Accordingly, idiopathic and pristane-induced systemic autoimmunity require both type I interferon and proinflammatory cytokines whereas the less aggressive mercury-induced autoimmunity, although dependent on nucleic acid-binding toll-like receptors, does not require type I interferon but needs proinflammatory cytokines. Scavenger receptors and the inflammasome may contribute to silica-induced autoimmunity. Greater understanding of the innate mechanisms responsible for idiopathic and environmentally induced autoimmunity should yield new information into the processes that instigate and drive systemic autoimmunity.

Overexpression of apolipoprotein A1 in the lung abrogates fibrosis in experimental silicosis

The inhalation of silica particles induces silicosis, an inflammatory and fibrotic lung disease characterized by the early accumulation of macrophages and neutrophils in the airspace and subsequent appearance of silicotic nodules as a result of progressive fibrosis. This study evaluated whether apolipoprotein A1 (ApoA1) protects against ongoing fibrosis and promotes the resolution of established experimental lung silicosis. Crystallized silica was intratracheally administered to 6- to 8-week-old transgenic mice expressing human ApoA1 in their alveolar epithelial cells (day 0). ApoA1 was overexpressed beginning on day 7 (ApoA1_D7 group) or day 15 (ApoA1_D15 group). The mice were sacrificed on day 30 for an evaluation of lung histology; the measurement of collagen, transforming growth factor-b1 and lipoxin A4; and a TUNEL assay for apoptotic cells. The ApoA1_D7 and D15 groups showed significant reductions in the silica-induced increase in inflammatory cells, silicotic nodule area, and collagen deposition compared with the silica-treated ApoA1 non-overexpressing mice. The level of transforming growth factor-b1 decreased in the bronchoalveolar lavage fluid, whereas lipoxin A4 was increased in the ApoA1_D7 and D15 groups compared with the silica-treated ApoA1 non-overexpressing mice. The silica-induced increase in the number of apoptotic cells was significantly reduced in the lungs of mice overexpressing ApoA1. Overexpression of ApoA1 decreased silica-induced lung inflammation and fibrotic nodule formation. The restoration of lipoxin A4 may contribute to the protective effect of ApoA1 overexpression against silica-induced lung fibrosis.

Cytokines in chronic respiratory diseases

Cytokines are small, secreted proteins that control immune responses. Within the lung, they can control host responses to injuries or infection, resulting in clearance of the insult, repair of lung tissue, and return to homeostasis. Problems can arise when this response is over exuberant and/or cytokine production becomes dysregulated. In such cases, chronic and repeated inflammatory reactions and cytokine production can be established, leading to airway remodeling and fibrosis with unintended, maladaptive consequences. In this report, we describe the cytokines and molecular mechanisms behind the pathology observed in three major chronic diseases of the lung: asthma, chronic obstructive pulmonary disease (COPD), and pulmonary fibrosis. Overlapping mechanisms are presented as potential sites for therapeutic intervention.

Negative regulation of pulmonary Th17 responses by C3a anaphylatoxin during allergic inflammation in mice

Activation of complement is one of the earliest immune responses to exogenous threats, resulting in various cleavage products including anaphylatoxin C3a. In addition to its contribution to host defense, C3a has been shown to mediate Th2 responses in animal models of asthma. However, the role of C3a on pulmonary Th17 responses during allergic inflammation remains unclear. Here, we show that mice deficient in C3a receptor (C3aR) exhibited (i) higher percentages of endogenous IL-17-producing CD4⁺ T cells in the lungs, (ii) higher amounts of IL-17 in the bronchoalveolar lavage fluid, and (iii) more neutrophils in the lungs than wild-type mice when challenged with intranasal allergens. Moreover, adoptive transfer experiments showed that the frequencies of antigen-specific IL-17-producing CD4⁺ T cells were significantly higher in the lungs and bronchial lymph nodes of C3aR-deficient recipients than those of wild-types recipients. Bone-marrow reconstitution study indicated that C3aR-deficiency on hematopoietic cells was required for the increased Th17 responses. Furthermore, C3aR-deficient mice exhibited increased percentages of Foxp3⁺ regulatory T cells; however, depletion of these cells minimally affected the induction of antigen-specific Th17 cell population in the lungs. Neutralization of IL-17 significantly reduced the number of neutrophils in bronchoalveolar lavage fluid of C3aR-deficient mice. Our findings demonstrate that C3a signals negatively regulate antigen-specific Th17 responses during allergic lung inflammation and the size of Foxp3⁺ regulatory T cell population in the periphery.

Significance of the balance between regulatory T (Treg) and T helper 17 (Th17) cells during hepatitis B virus related liver fibrosis

Background

Hepatitis B virus-related liver fibrosis (HBV-LF) always progresses from inflammation to fibrosis. However, the relationship between these two pathological conditions is not fully understood. Here, it is postulated that the balance between regulatory T (Treg) cells and T helper 17 (Th17) cells as an indicator of inflammation may predict fibrosis progression of HBV-LF.

Methodology/Principal Findings

The frequencies and phenotypes of peripheral Treg and Th17 cells of seventy-seven HBeAg-positive chronic hepatitis B (CHB) patients who underwent liver biopsies and thirty healthy controls were determined by flow cytometry. In the periphery of CHB patients, both Treg and Th17 frequencies were significantly increased and correlated, and a lower Treg/Th17 ratio always indicated more liver injury and fibrosis progression. To investigate exact effects of Treg and Th17 cells during HBV-LF, a series of in vitro experiments were performed using purified CD4⁺, CD4⁺CD25⁺, or CD4⁺CD25⁻ cells from the periphery, primary human hepatic stellate cells (HSCs) isolated from healthy liver specimens, human recombinant interleukin (IL)-17 cytokine, anti-IL-17 antibody and HBcAg. In response to HBcAg, CD4⁺CD25⁺ cells significantly inhibited cell proliferation and cytokine production (especially IL-17 and IL-22) by CD4⁺CD25⁻ cells in cell-contact and dose-dependent manners. In addition, CD4⁺ cells from CHB patients, compared to those from HC subjects, dramatically promoted proliferation and activation of human HSCs. Moreover, in a dramatically dose-dependent manner, CD4⁺CD25⁺ cells from CHB patients inhibited, whereas recombinant IL-17 response promoted the proliferation and activation of HSCs. Finally, in vivo evidence about effects of Treg/Th17 balance during liver fibrosis was obtained in concanavalin A-induced mouse fibrosis models via depletion of CD25⁺ or IL-17⁺ cells, and it’s observed that CD25 depletion promoted, whereas IL-17 depletion, alleviated liver injury and fibrosis progression.

Conclusions/Significance

The Treg/Th17 balance might influence fibrosis progression in HBV-LF via increase of liver injury and promotion of HSCs activation.

Tregs promote the differentiation of Th17 cells in silica-induced lung fibrosis in mice

Background

Silicosis is an occupational lung disease caused by inhalation of silica dust and characterized by lung inflammation and fibrosis. Previous study showed that Tregs regulate the process of silicosis by modulating the maintenance of immune homeostasis in the lung. Th17 cells share reciprocal developmental pathway with Tregs and play a pivotal role in the immunopathogenesis of many lung diseases by recruiting and activating neutrophils, but the regulatory function of Tregs on Th17 response in silica induced lung fibrosis remains to be explored.

Methodology/Principal Findings

To evaluate the role of Th17 and IL-17 in the development of silicosis and their interaction with Tregs, Treg-depleted mice model was generated and exposed to silica to establish experimental model of silica-induced lung fibrosis. Here we showed that silica increased Th17 response in lung fibrosis. Tregs depletion enhanced the neutrophils accumulation and attenuated Th17 response in silica induced lung fibrosis. Both mRNA and protein results showed that Tregs exerted its modulatory function on Th17 cells and IL-17 by regulating TGF-β1 and IL-1β.

Conclusion/Significance

Our study suggested that Tregs could promote Th17 cells differentiation by regulating TGF-β1 and IL-1β in silica induced lung fibrosis of mice, which further the understanding of the progress of silicosis and provide a new insight in the regulatory mechanism of Th17 by Tregs in lung inflammation.

Aryl hydrocarbon receptor (AhR) regulates silica-induced inflammation but not fibrosis

The aryl hydrocarbon receptor (AhR), a ligand-activated transcription factor, is responsible for mediating a variety of pharmacological and toxicological effects caused by halogenated aromatic hydrocarbons such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). However, recent evidence has revealed that the AhR also has numerous physiological roles aside from xenobiotic metabolism, including regulation of immune and inflammatory signaling as well as normal development and homeostasis of several organs. To investigate the role of the AhR in crystalline silica (SiO(2))-induced inflammation and fibrosis, C57Bl/6 and AhR(-/)(-) mice were exposed to SiO(2) or vehicle. Similarly, C57Bl/6 mice were exposed to SiO(2) and TCDD either simultaneously or sequentially to assess whether AhR activation alters inflammation and fibrosis. SiO(2)-induced acute lung inflammation was more severe in AhR(-)(/-) mice; however, the fibrotic response of AhR(-)(/-) mice was attenuated compared with C57Bl/6 mice. In a model of chronic SiO(2) exposure, AhR activation by TCDD in C57Bl/6 mice resulted in reduced inflammation; however, the fibrotic response was not affected. Bone marrow-derived macrophages (BMM) from AhR(-)(/-) mice also produced higher levels of cytokines and chemokines in response to SiO(2). Analysis of gene expression revealed that BMM derived from AhR(-)(/-) mice exhibit increased levels of pro-interleukin (IL)-1β, IL-6, and Bcl-2, yet decreased levels of signal transducers and activators of transcription (STAT)2, STAT5a, and serpin B2 (Pai-2) in response to SiO(2).

Anti-cytokine auto-vaccinations as tools for the analysis of cytokine function in vivo

Braking B cell tolerance to generate antibodies against autologous cytokines or chemokines offers an alternative to gene inactivation for functional analysis of these factors in vivo. It is clearly less potent than the genetic approach but offers the advantage of extreme flexibility. The basic principle is to enable a self-reactive B cell to attract T cell help by presenting foreign peptides, a process we called "deceptive" antigen presentation. We here review the different auto-vaccine procedures that are currently used and provide several examples of functional information acquired by this procedure or by mAbs derived from auto-vaccinated mice.

Increased IL-17-producing CD4(+) T cells in patients with esophageal cancer

Increased interleukin-17 (IL-17)-producing Th (Th17) cells have been described in a variety of human carcinoma cases, however, the mechanism of Th17 cells' accumulation in a tumor microenvironment remains elusive. This study was designed to investigate whether Th17 cells were involved in the development of esophageal cancer. We found that the proportion of Th17 cells increased within the peripheral blood and tumor tissues of esophageal cancer patients. Furthermore, the proportion of circulating Th17 cells was higher in advanced esophageal cancer patients than that in early esophageal cancer patients. In addition, the Th17 cells differentiation-related cytokines (IL-23, IL-1β, and IL-6) and accumulation-related chemokines (CCL22 and CCL20) were present in a tumor microenvironment. Therefore, the findings may partly explain the cause for the increased proportion of Th17 cells and indicate a potential prognostic marker of Th17 cells in esophageal cancer.

Platelet-derived growth factor-producing CD4+ Foxp3+ regulatory T lymphocytes promote lung fibrosis

RATIONALE

There is evidence that CD4(+) effector T lymphocytes (T eff) participate in the development of lung fibrosis, but the role of their CD4(+) regulatory T-cell (T reg) counterparts remains to be determined.

OBJECTIVES

To elucidate the contribution of T reg cells in a mouse model of lung fibrosis induced by silica (SiO(2)) particles.

METHODS

Lung T reg and T eff cells purified from SiO(2)-treated Foxp3-GFP transgenic mice were cocultured with naive lung fibroblasts or transferred to the lungs of healthy mice. DEREG mice, which express the diphtheria toxin receptor under the control of the foxp3 gene, were used to deplete T reg cells during fibrogenesis.

MEASUREMENTS AND MAIN RESULTS

CD4(+) Foxp3(+) T reg cells were persistently recruited in the lungs in response to SiO(2). T reg accumulation paralleled the establishment of pulmonary immunosuppression and fibrosis. T reg cells highly expressed platelet-derived growth factor (PDGF)-B via a TGF-β autocrine signaling pathway, directly stimulated fibroblast proliferation in vitro, and increased lung collagen deposition upon transfer in the lung of naive mice. The direct profibrotic effects of T reg cells were abolished by the inhibitor of the PDGF-B/TGF-β signaling pathway, imatinib mesylate. Neutralization of T reg-immunosuppressive activity resulted in enhanced accumulation of T eff cells and IL-4-driven pulmonary fibrogenesis, further demonstrating that T reg cells control T eff cell functions during inflammatory fibrosis.

CONCLUSIONS

Our study indicates that T reg cells contribute to lung fibrosis by stimulating fibroblasts through the secretion of PDGF-B in noninflammatory conditions and regulate detrimental T eff cell activities during inflammation-related fibrosis.

Epithelial transglutaminase 2 is needed for T cell interleukin-17 production and subsequent pulmonary inflammation and fibrosis in bleomycin-treated mice

Inhibition of transglutaminase 2 reduces bleomycin-induced epithelial cell release of interleukin 6 in vitro and pulmonary inflammation and fibrosis in vivo.

Pulmonary fibrosis is a potentially life-threatening disease that may be caused by overt or asymptomatic inflammatory responses. However, the precise mechanisms by which tissue injury is translated into inflammation and consequent fibrosis remain to be established. Here, we show that in a lung injury model, bleomycin induced the secretion of IL-6 by epithelial cells in a transglutaminase 2 (TG2)–dependent manner. This response represents a key step in the differentiation of IL-17–producing T cells and subsequent inflammatory amplification in the lung. The essential role of epithelial cells, but not inflammatory cells, TG2 was confirmed in bone marrow chimeras; chimeras made in TG2-deficient recipients showed reduced inflammation and fibrosis, compared with those in wild-type mice, regardless of the bone marrow cell phenotype. Epithelial TG2 thus appears to be a critical inducer of inflammation after noninfectious pulmonary injury. We further demonstrated that fibroblast-derived TG2, acting downstream of transforming growth factor-β, is also important in the effector phase of fibrogenesis. Therefore, TG2 represents an interesting potential target for therapeutic intervention.

Regulation and function of IL-17A- and IL-22-producing γδ T cells

The regulation of IL-17A and IL-22 production differs between human and murine γδ T cells. We find that human γδ T cells expressing Vγ2Vδ2 T cell receptors are peripherally polarized to produce IL-17A or IL-22, much like CD4 αβ Th17 T cells. This requires IL-6, IL-1β, and TGF-β, whereas expansion and maintenance requires IL-23, IL-1β, and TGF-β. In contrast, IL-17A and IL-22 production by murine γδ T cells is innately programmed during thymic ontogeny but requires IL-23 and IL-1β for maintenance. Murine γδ cells producing IL-17A and IL-22 play important roles in microbial, autoimmune, and inflammatory responses. However, the roles played by human IL-17A- and IL-22-producing γδ T cells are less clear but are also likely to be important. These observations highlight differences between humans and murine γδ T cells and underscore the importance of IL-17A- and IL-22-producing γδ T cells.

γδ T cells attenuate bleomycin-induced fibrosis through the production of CXCL10

γδ T cells are a subset of T cells associated with epithelial mucosal tissues and play a prominent role in both promoting and dampening inflammatory responses to pathogens; in addition, they strongly mediate epithelial repair. By using a bleomycin model of pulmonary fibrosis, we found that γδ T-cell populations dramatically increased after bleomycin administration. To determine the importance of these cells, we exposed mice lacking the δ chain of the γδ T-cell receptor (γδ knockout [KO]) to bleomycin. Pulmonary fibrosis was more severe in γδ KO mice, as measured by collagen deposition (hydroxyproline) and histopathological features. Furthermore, there was no evidence of resolution of the fibrotic response up to 45 days after bleomycin therapy. In contrast to control mice, γδ KO mice had decreased concentrations of IL-6, granulocyte colony stimulating factor, chemokine CXC ligand (CXCL) 1, and interferon inducible protein 10/CXCL10. In vitro culture of γδ T cells purified from lungs 17 days after bleomycin exposure (a time of peak influx of these cells) demonstrated that γδ T cells produced substantial quantities of all four of these cytokines, suggesting that γδ T cells are a predominant source of these proteins. To demonstrate that γδ T cells are effector cells in the fibrotic response, we performed adoptive transfer experiments with γδ T cells sorted from bleomycin-treated lungs; these cells were sufficient to resolve fibrosis in γδ KO mice and restore CXCL10 levels comparable to wild-type mice. Furthermore, overexpression of CXCL10 in the lung decreased the severity of fibrosis seen in the γδ KO mice. Finally, adoptive transfer of γδ T cells from CXCL10(-/-) mice failed to reverse the severe fibrosis in γδ KO mice. These results indicate that γδ T cells promote the resolution of fibrosis through the production of CXCL10.

Burn induces a Th-17 inflammatory response at the injury site

INTRODUCTION

The high incidence of morbidity and mortality following major burn can be in part attributed to immune dysfunction and wound healing complications. Inflammation plays a major role in the complex process of wound repair. Recently, a novel class of T-helper cells, termed Th-17 cells, has been found to secrete the pro-inflammatory cytokines IL-17 and IL-22. The Th-17 response also involves other cytokines, such as IL-6 and TGF-β, which have been shown to be associated with burn-induced inflammation. Nonetheless, the relationships between the Th-17 response and post-burn inflammation are unknown.

METHODS

C57BL/6 male mice (n = 5-6/group) were subjected to a major burn (25% TBSA) or sham procedure. Three hours thereafter, skin samples were collected (uninjured skin and burn skin) and processed for the determination of Th-17 cytokine (IL-6, IL-17, IL-22, IL-23, IL-27, and TGF-β) levels by ELISA.

RESULTS

At 3h after burn a significant (~3-fold) increase in tissue levels of IL-17 and IL-22 was observed at the burn site as compared to sham skin. The burn-induced Th-17 response was independent of statistically significant changes in other Th-17 cytokines (i.e., IL-6, IL-23, IL-27 and TGF-β).

CONCLUSIONS

These findings indicate the development of a robust Th-17 response at the burn site that may play an important role in subsequent immune and wound healing derangements.

Fibrogenic and redox-related but not proinflammatory genes are upregulated in Lewis rat model of chronic silicosis

Silicosis, a fibrotic granulomatous lung disease, may occur through accidental high-dose or occupational inhalation of silica, leading to acute/accelerated and chronic silicosis, respectively. While chronic silicosis has a long asymptomatic latency, lung inflammation and apoptosis are hallmarks of acute silicosis. In animal models, histiocytic granulomas develop within days after high-dose intratracheal (IT) silica instillation. However, following chronic inhalation of occupationally relevant doses of silica, discrete granulomas resembling human silicosis arise months after the final exposure without significant lung inflammation/apoptosis. To identify molecular events associated with chronic silicosis, lung RNA samples from controls or subchronic silica-exposed rats were analyzed by Affymetrix at 28 wk after silica exposures. Results suggested a significant upregulation of 144 genes and downregulation of 7 genes. The upregulated genes included complement cascade, chemokines/chemokine receptors, G-protein signaling components, metalloproteases, and genes associated with oxidative stress. To examine the kinetics of gene expression relevant to silicosis, quantitative polymerase chain reaction (qPCR), enzyme-linked immunosorbent assay (ELISA), Luminex-bead assays, Western blotting, and/or zymography were performed on lung tissues from 4 d, 28 wk, and intermediate times after subchronic silica exposure and compared with 14-d acute silicosis samples. Results indicated that genes regulating fibrosis (secreted phosphoprotein-1, Ccl2, and Ccl7), redox enzymes (superoxide dismutase-2 and arginase-1), and the enzymatic activities of matrix metalloproteinases 2 and 9 were upregulated in acute and chronic silicosis models. However, proinflammatory cytokines were strongly upregulated only in acute silicosis. Thus, inflammatory cytokines are associated with acute but not chronic silicosis. Data suggest that genes regulating fibrosis, oxidative stress, and metalloproteases may contribute to both acute and chronic silicosis.

Aerobiology and inhalation exposure to biological select agents and toxins

Aerosol is the most likely route of dissemination of biological select agents and toxins in a bioterrorist attack, regardless of the natural route of exposure to the agent. The use of animal models for testing preventative and therapeutic countermeasures requires knowledge of the pathogenesis of disease after inhalation exposure. Factors that relate to outcome after respiratory exposure include the inherent infectivity and virulence and/or toxicity of the agent in the host under investigation, in addition to characteristics of the aerosol particle and host that affect the delivered dose of, and host response to, the inhaled material. This introductory article discusses the emerging science of aerobiology and the unique features of respiratory tract anatomy, physiology, and immunology that are relevant to the pathogenesis of aerosolized biothreat agents.