The regulatory role of interferon-γ producing gamma delta T cells via the suppression of T helper 17 cell activity in bleomycin-induced pulmonary fibrosis

Effects of Natural Products through Inhibiting Endoplasmic Reticulum Stress on Attenuation of Idiopathic Pulmonary Fibrosis

With ever-increasing intensive studies of idiopathic pulmonary fibrosis (IPF), significant progresses have been made. Endoplasmic reticulum stress (ERS)/unfolded protein reaction (UPR) is associated with the development and progression of IPF, and targeting ERS/UPR may be beneficial in the treatment of IPF. Natural product is a tremendous source of new drug discovery, and accumulating studies have reported that many natural products show potential therapeutic effects for IPF via modulating one or more branches of the ERS signaling pathway. Therefore, this review focuses on critical roles of ERS in IPF development, and summarizes herbal preparations and bioactive compounds which protect against IPF through regulating ERS.

The Role of Immune Cells in the Pathogenesis of Idiopathic Pulmonary Fibrosis

Idiopathic pulmonary fibrosis (IPF) is a devastating disease of unknown etiology with limited treatment options. The role of the immune system in IPF has received increasing attention. Uncontrolled immune responses drive the onset and progression of IPF. This article provides an overview of the role of innate immune cells (including macrophages, neutrophils, mast cells, eosinophils, dendritic cells, nature killer cells, nature kill cells and γδ T cells) and adaptive immune cells (including Th1 cells, Th2 cells, Th9 cells, Th17 cells, Th22 cells, cytotoxic T cells, B lymphocytes and Treg cells) in IPF. In addition, we review the current status of pharmacological treatments for IPF and new developments in immunotherapy. A deeper comprehension of the immune system's function in IPF may contribute to the development of targeted immunomodulatory therapies that can alter the course of the disease.

Pulmonary fibrosis and type-17 immunity

Fibrosis of the lung can occur in idiopathic pulmonary fibrosis, collagen vascular diseases, and hypersensitivity pneumonitis, among other diseases. Transforming growth factor (TGF)-β, vascular epithelial growth factor, fibroblast growth factor, and platelet-derived growth factor contribute to the pathophysiology of fibrosis. TGF-β and other cytokines, including interleukin (IL)-1β, IL-6, and IL-23, activate type-17 immunity, which is involved in pulmonary fibrosis. The components of type-17 immunity include type-17 helper T cells, γδT cells, IL-17A-producing CD8-positive T cells, invariant NKT cells, and group 3 innate lymphoid cells. IL-17A, the main cytokine of type-17 immunity, is able to induce the epithelial-mesenchymal transition in epithelial cells via a production of TGF-β, directly stimulate fibroblasts and fibrocytes, and inhibit autophagy, which otherwise protects against pulmonary fibrosis. IL-23 induces type-17 immunity and plays an important role in the acute exacerbation of pulmonary fibrosis. Clinical studies have also linked type-17 immunity to the pathogenesis of pulmonary fibrosis. Consequently, targeting type-17 immunity may serve as a new therapeutic strategy to prevent the development or exacerbation of pulmonary fibrosis.

Inhibition of Th17 cells by donepezil ameliorates experimental lung fibrosis and pulmonary hypertension

Rationale: Pulmonary hypertension (PH) secondary to lung fibrosis belongs to WHO Group III, one of the most common subgroups of PH; however, it lacks effective treatment options. Cholinesterase inhibitor donepezil (DON) has been shown to effectively improve Group I PH. However, its effects on Group III PH are unknown. Methods: A lung fibrosis-induced PH mouse model was constructed using a single intratracheal instillation of bleomycin (BLM), after which DON was administered daily. Pulmonary artery and right ventricle (RV) remodeling were evaluated at the end of the study. Lung tissue in each group was analyzed using RNA sequencing, and the results were further verified with datasets from patients with PH. The mechanisms underlying DON-induced effects on PH were verified both in vivo and in vitro. Results: DON effectively improved pulmonary artery and RV remodeling in the BLM-induced mouse model. Transcriptomic profiles of lung tissue indicated that the expression of inflammatory and fibrotic genes was significantly changed in this process. In the animal model and patients with PH, T helper 17 lymphocytes (Th17) were the most common inflammatory cells infiltrating the lung tissue. DON significantly inhibited lung fibroblast activation; thus, preventing lung fibrosis and reducing the inflammatory response and Th17 cell infiltration in the BLM-induced lung tissue. In addition, Th17 cells could activate lung fibroblasts by secreting IL17A, and DON-mediated inhibition of Th17 cell differentiation was found to depend on the α7nAchR-JAK2-STAT3 pathway. Conclusion: DON can alleviate lung fibrosis and PH in an experimental mouse model. It inhibited pro-inflammatory Th17 cell differentiation, which is dependent on a cholinergic receptor pathway, thereby regulating fibroblast activation.

Neuropeptide Y Antagonizes Development of Pulmonary Fibrosis through IL-1β Inhibition

Neuropeptide Y (NPY), a 36 amino acid residue polypeptide distributed throughout the nervous system, acts on various immune cells in many organs, including the respiratory system. However, little is known about its role in the pathogenesis of pulmonary fibrosis. This study was performed to determine the effects of NPY on pulmonary fibrosis. NPY-deficient and wild-type mice were intratracheally administered bleomycin. Inflammatory cells, cytokine concentrations, and morphological morphometry of the lungs were analyzed. Serum NPY concentrations were also measured in patients with idiopathic pulmonary fibrosis and healthy control subjects. NPY-deficient mice exhibited significantly enhanced pulmonary fibrosis and higher IL-1β concentrations in the lungs compared with wild-type mice. Exogenous NPY treatment suppressed the development of bleomycin-induced lung fibrosis and decreased IL-1β concentrations in the lungs. Moreover, IL-1β neutralization in NPY-deficient mice attenuated the fibrotic changes. NPY decreased IL-1β release, and Y1 receptor antagonists inhibited IL-1β release and induced epithelial-mesenchymal transition in human alveolar epithelial cells. Patients with idiopathic pulmonary fibrosis had lower NPY and greater IL-1β concentrations in the serums compared with healthy control subjects. NPY expression was mainly observed around bronchial epithelial cells in human idiopathic pulmonary fibrosis lungs. These data suggest that NPY plays a protective role against pulmonary fibrosis by suppressing IL-1β release, and manipulating the NPY-Y1 receptor axis could be a potential therapeutic strategy for delaying disease progression.

Allies or enemies? The effect of regulatory T cells and related T lymphocytes on the profibrotic environment in bleomycin-injured lung mouse models

Idiopathic pulmonary fibrosis (IPF) is characterized by permanent scarring of lung tissue and declining lung function, and is an incurable disease with increase in prevalence over the past decade. The current consensus is that aberrant wound healing following repeated injuries to the pulmonary epithelium is the most probable cause of IPF, with various immune inflammatory pathways having been reported to impact disease pathogenesis. While the role of immune cells, specifically T lymphocytes and regulatory T cells (Treg), in IPF pathogenesis has been reported and discussed recently, the pathogenic or beneficial roles of these cells in inducing or preventing lung fibrosis is still debated. This lack of understanding could be due in part to the difficulty in obtaining diseased human lung tissue for research purposes. For this reason, many animal models have been developed over the years to attempt to mimic the main clinical hallmarks of IPF: among these, inducing lung injury in rodents with the anti-cancer agent bleomycin has now become the most commonly studied animal model of IPF. Pulmonary fibrosis is the major side effect when bleomycin is administered for cancer treatment in human patients, and a similar effect can be observed after intra-tracheal administration of bleomycin to rodents. Despite many pathophysiological pathways of lung fibrosis having been investigated in bleomycin-injured animal models, one central facet still remains controversial, namely the involvement of specific T lymphocyte subsets, and in particular Treg, in disease pathogenesis. This review aims to summarize the major findings and conclusions regarding the involvement of immune cells and their receptors in the pathogenesis of IPF, and to elaborate on important parallels between animal models and the human disease. A more detailed understanding of the role of Treg and other immune cell subsets in lung injury and fibrosis derived from animal models is a critical basis for translating this knowledge to the development of new immune-based therapies for the treatment of human IPF.

Two Distinct Mechanisms Underlying γδ T Cell-Mediated Regulation of Collagen Type I in Lung Fibroblasts

Idiopathic pulmonary fibrosis is a chronic intractable lung disease, leading to respiratory failure and death. Although anti-fibrotic agents delay disease progression, they are not considered curative treatments, and alternative modalities have attracted attention. We examined the effect of human γδ T cells on collagen type I in lung fibroblasts. Collagen type I was markedly reduced in a γδ T cell number-dependent manner following treatment with γδ T cells expanded with tetrakis-pivaloxymethyl 2-(thiazole-2-ylamino) ethylidene-1,1-bisphosphonate (PTA) and interleukin-2. Collagen type I levels remained unchanged on addition of γδ T cells to the culture system through a trans-well culture membrane, suggesting that cell–cell contact is essential for reducing its levels in lung fibroblasts. Re-stimulating γδ T cells with (E)-4-hydroxy-3-methylbut-2-enyl diphosphate (HMBPP) reduced collagen type I levels without cell–cell contact, indicating the existence of HMBPP-induced soluble anti-fibrotic factors in γδ T cells. Adding anti-interferon-γ (IFN-γ)-neutralizing mAb restored collagen type I levels, demonstrating that human γδ T cell-derived IFN-γ reduces collagen type I levels. Conversely, interleukin-18 augmented γδ T cell-induced suppression of collagen type I. Therefore, human γδ T cells reduce collagen levels in lung fibroblasts via two distinct mechanisms; adoptive γδ T cell transfer is potentially a new therapeutic candidate.

The role of immune response in the pathogenesis of idiopathic pulmonary fibrosis: far beyond the Th1/Th2 imbalance

INTRODUCTION

. Idiopathic pulmonary fibrosis (IPF) is a chronic disease of unknown origin characterized by progressive scarring of the lung leading to irreversible loss of function. Despite the availability of two drugs that are able to slow down disease progression, IPF remains a deadly disease. The pathogenesis of IPF is poorly understood, but a dysregulated wound healing response following recurrent alveolar epithelial injury is thought to be crucial. Areas covered. In the last few years, the role of the immune system in IPF pathobiology has been reconsidered; indeed, recent data suggest that a dysfunctional immune system may promote and unfavorable interplay with pro-fibrotic pathways thus acting as a cofactor in disease development and progression. In this article, we review and critically discuss the role of T cells in the pathogenesis and progression of IPF in the attempt to highlight ways in which further research in this area may enable the development of targeted immunomodulatory therapies for this dreadful disease.

EXPERT OPINION

A better understanding of T cells interactions has the potential to facilitate the development of immune modulators targeting multiple T cell-mediated pathways thus halting disease initiation and progression.

Hallmarks of Resistance to Immune-Checkpoint Inhibitors

Immune-checkpoint inhibitors (ICI), although revolutionary in improving long-term survival outcomes, are mostly effective in patients with immune-responsive tumors. Most patients with cancer either do not respond to ICIs at all or experience disease progression after an initial period of response. Treatment resistance to ICIs remains a major challenge and defines the biggest unmet medical need in oncology worldwide. In a collaborative workshop, thought leaders from academic, biopharma, and nonprofit sectors convened to outline a resistance framework to support and guide future immune-resistance research. Here, we explore the initial part of our effort by collating seminal discoveries through the lens of known biological processes. We highlight eight biological processes and refer to them as immune resistance nodes. We examine the seminal discoveries that define each immune resistance node and pose critical questions, which, if answered, would greatly expand our notion of immune resistance. Ultimately, the expansion and application of this work calls for the integration of multiomic high-dimensional analyses from patient-level data to produce a map of resistance phenotypes that can be utilized to guide effective drug development and improved patient outcomes.

Mechanism of Fei-Xian Formula in the Treatment of Pulmonary Fibrosis on the Basis of Network Pharmacology Analysis Combined with Molecular Docking Validation

Objective

This study aimed to clarify the mechanism of Fei-Xian formula (FXF) in the treatment of pulmonary fibrosis based on network pharmacology analysis combined with molecular docking validation.

Methods

Firstly, ingredients in FXF with pharmacological activities, together with specific targets, were identified based on the BATMA-TCM and TCMSP databases. Then, targets associated with pulmonary fibrosis, which included pathogenic targets as well as those known therapeutic targets, were screened against the CTD, TTD, GeneCards, and DisGeNet databases. Later, Cytoscape was employed to construct a candidate component-target network of FXF for treating pulmonary fibrosis. In addition, for nodes within the as-constructed network, topological parameters were calculated using CytoHubba plug-in, and the degree value (twice as high as the median degree value for all the nodes) was adopted to select core components as well as core targets of FXF for treating pulmonary fibrosis, which were subsequently utilized for constructing the core network. Furthermore, molecular docking study was carried out on those core active ingredients together with the core targets using AutoDock Vina for verifying results of network pharmacology analysis. At last, OmicShare was employed for enrichment analysis of the core targets.

Results

Altogether 12 active ingredients along with 13 core targets were identified from our constructed core component-target network of FXF for the treatment of pulmonary fibrosis. As revealed by enrichment analysis, the 13 core targets mostly concentrated in regulating biological functions, like response to external stimulus (from oxidative stress, radiation, UV, chemical substances, and virus infection), apoptosis, cell cycle, aging, immune process, and protein metabolism. In addition, several pathways, like IL-17, AGE-RAGE, TNF, HIF-1, PI3K-AKT, NOD-like receptor, T/B cell receptor, and virus infection-related pathways, exerted vital parts in FXF in the treatment of pulmonary fibrosis.

Conclusions

FXF can treat pulmonary fibrosis through a “multicomponent, multitarget, and multipathway” mean. Findings in this work lay foundation for further exploration of the FXF mechanism in the treatment of pulmonary fibrosis.

The Roles of Immune Cells in the Pathogenesis of Fibrosis

Tissue injury and inflammatory response trigger the development of fibrosis in various diseases. It has been recognized that both innate and adaptive immune cells are important players with multifaceted functions in fibrogenesis. The activated immune cells produce various cytokines, modulate the differentiation and functions of myofibroblasts via diverse molecular mechanisms, and regulate fibrotic development. The immune cells exhibit differential functions during different stages of fibrotic diseases. In this review, we summarized recent advances in understanding the roles of immune cells in regulating fibrotic development and immune-based therapies in different disorders and discuss the underlying molecular mechanisms with a focus on mTOR and JAK-STAT signaling pathways.

T Cells in Fibrosis and Fibrotic Diseases

Fibrosis is the extensive deposition of fibrous connective tissue, and it is characterized by the accumulation of collagen and other extracellular matrix (ECM) components. Fibrosis is essential for wound healing and tissue repair in response to a variety of triggers, which include infection, inflammation, autoimmune disorder, degenerative disease, tumor, and injury. Fibrotic remodeling in various diseases, such as liver cirrhosis, pulmonary fibrosis, renal interstitial fibrosis, myocardial infarction, systemic sclerosis (SSc), and graft-versus-host disease (GVHD), can impair organ function, causing high morbidity and mortality. Both innate and adaptive immunity are involved in fibrogenesis. Although the roles of macrophages in fibrogenesis have been studied for many years, the underlying mechanisms concerning the manner in which T cells regulate fibrosis are not completely understood. The T cell receptor (TCR) engages the antigen and shapes the repertoire of antigen-specific T cells. Based on the divergent expression of surface molecules and cell functions, T cells are subdivided into natural killer T (NKT) cells, γδ T cells, CD8⁺ cytotoxic T lymphocytes (CTL), regulatory T (Treg) cells, T follicular regulatory (Tfr) cells, and T helper cells, including Th1, Th2, Th9, Th17, Th22, and T follicular helper (Tfh) cells. In this review, we summarize the pro-fibrotic or anti-fibrotic roles and distinct mechanisms of different T cell subsets. On reviewing the literature, we conclude that the T cell regulations are commonly disease-specific and tissue-specific. Finally, we provide perspectives on microbiota, viral infection, and metabolism, and discuss the current advancements of technologies for identifying novel targets and developing immunotherapies for intervention in fibrosis and fibrotic diseases.

Deficiency of CRTH2, a Prostaglandin D2 Receptor, Aggravates Bleomycin-induced Pulmonary Inflammation and Fibrosis

Chemoattractant receptor homologous with T-helper cell type 2 cells (CRTH2), a receptor for prostaglandin D₂, is preferentially expressed on T-helper cell type 2 lymphocytes, group 2 innate lymphoid cells, eosinophils, and basophils, and elicits the production of type 2 cytokines, including profibrotic IL-13. We hypothesized that lack of CRTH2 might protect against fibrotic lung disease, and we tested this hypothesis using a bleomycin-induced lung inflammation and fibrosis model in CRTH2-deficient (CRTH2^-/-) or wild-type BALB/c mice. Compared with wild-type mice, CRTH2^-/- mice treated with bleomycin exhibited significantly higher mortality, enhanced accumulation of inflammatory cells 14-21 days after bleomycin injection, reduced pulmonary compliance, and increased levels of collagen and total protein in the lungs. These phenotypes were associated with decreased levels of IFN-γ, IL-6, IL-10, and IL-17A in BAL fluid. Adoptive transfer of splenocytes from wild-type, but not CRTH2^-/-, mice 2 days before injection of bleomycin resolved the sustained inflammation as well as the increased collagen and protein accumulation in the lungs of CRTH2^-/- mice. We consider that the disease model is driven by γδT cells that express CRTH2; thus, the adoptive transfer of γδT cells could ameliorate bleomycin-induced alveolar inflammation and fibrosis.

Association of Decreased Percentage of Vδ2+Vγ9+ γδ T Cells With Disease Severity in Multiple Sclerosis

We recently reported that deletion-type copy number variations of the T cell receptor (TCR) γ, α, and δ genes greatly enhanced susceptibility to multiple sclerosis (MS). However, the effect of abnormal TCR γδ gene rearrangement on MS pathogenesis remains unknown. In the present study, we aimed to clarify γδ TCR repertoire alterations and their relationship to clinical and immunological parameters in MS patients by comprehensive flow cytometric immunophenotyping. Peripheral blood mononuclear cells obtained from 30 untreated MS patients in remission and 23 age- and sex-matched healthy controls (HCs) were stained for surface markers and intracellular cytokines after stimulation with phorbol 12-myristate 13-acetate and ionomycin, and analyzed by flow cytometry. MS patients showed significantly decreased percentages of Vδ2⁺ and Vδ2⁺Vγ9⁺ cells in γδ T cells (p^corr = 0.0297 and p^corr = 0.0288, respectively) and elevated Vδ1/Vδ2 ratios compared with HCs (p = 0.0033). The percentages of interferon (IFN)-γ⁺Vδ2⁺ and interleukin (IL)-17A⁺IFN-γ⁺Vδ2⁺ cells in γδ T cells, as well as IFN-γ⁺ cells in Vδ2⁺ γδ T cells, were significantly lower in MS patients than in HCs (p^corr < 0.0009, p^corr = 0.0135, and p^corr = 0.0054, respectively). The percentages of Vδ2⁺ and Vδ2⁺Vγ9⁺ cells in γδ T cells were negatively correlated with both the Expanded Disability Status Scale score (r = -0.5006, p = 0.0048; and r = -0.5040, p = 0.0045, respectively) and Multiple Sclerosis Severity Score (r = -0.4682, p = 0.0091; and r = -0.4706, p = 0.0087, respectively), but not with age at disease onset, disease duration, or annualized relapse rate. In HCs, the percentages of Vδ2⁺ and Vδ2⁺Vγ9⁺ cells of total CD3⁺ T cells had strong positive correlations with the percentage of CD25⁺CD127^low/- cells in CD4⁺ T cells (r = 0.7826, p < 0.0001; and r = 0.7848, p < 0.0001, respectively), whereas such correlations were totally absent in MS patients. These findings suggest that decreased Vδ2⁺Vγ9⁺ γδ T cells are associated with disability in MS. Therefore, the Vδ1/Vδ2 ratio might be a candidate biomarker for predicting disease severity in MS.

The atypical chemokine receptor ACKR2 drives pulmonary fibrosis by tuning influx of CCR2+ and CCR5+ IFNγ-producing γδT cells in mice

Chemokines coordinate lung inflammation and fibrosis by acting on chemokine receptors expressed on leukocytes and other cell types. Atypical chemokine receptors (ACKRs) bind, internalize, and degrade chemokines, tuning homeostasis and immune responses. ACKR2 recognizes and decreases the levels of inflammatory CC chemokines. The role of ACKR2 in fibrogenesis is unknown. The purpose of the study was to investigate the role of ACKR2 in the context of pulmonary fibrosis. The effects of ACKR2 expression and deficiency during inflammation and fibrosis were analyzed using a bleomycin-model of fibrosis, ACKR2-deficient mice, bone marrow chimeras, and antibody-mediated leukocyte depletion. ACKR2 was upregulated acutely in response to bleomycin and normalized over time. ACKR2^-/- mice showed reduced lethality and lung fibrosis. Bone marrow chimeras showed that lethality and fibrosis depended on ACKR2 expression in pulmonary resident (nonhematopoietic) cells but not on leukocytes. ACKR2^-/- mice exhibited decreased expression of tissue-remodeling genes, reduced leukocyte influx, pulmonary injury, and dysfunction. ACKR2^-/- mice had early increased levels of CCL5, CCL12, CCL17, and IFNγ and an increased number of CCR2⁺ and CCR5⁺ IFNγ-producing γδT cells in the airways counterbalanced by low Th17-lymphocyte influx. There was reduced accumulation of IFNγ-producing γδT cells in CCR2^-/- and CCR5^-/- mice. Moreover, depletion of γδT cells worsened the clinical symptoms induced by bleomycin and reversed the phenotype of ACKR2^-/- mice exposed to bleomycin. ACKR2 controls the CC chemokine expression that drives the influx of CCR2⁺ and CCR5⁺ IFNγ-producing γδT cells, tuning the Th17 response that mediated pulmonary fibrosis triggered by bleomycin instillation.

Th17 cells contribute to pulmonary fibrosis and inflammation during chronic kidney disease progression after acute ischemia

Acute kidney injury (AKI) is associated with high mortality rates and predisposes development of chronic kidney disease (CKD). Distant organ damage, particularly in the lung, may contribute to mortality in AKI patients. Animal models of AKI demonstrate an increase in pulmonary infiltration of lymphocytes and reveal an acute compromise of lung function, but the chronic effects of AKI on pulmonary inflammation are unknown. We hypothesized that in response to renal ischemia/reperfusion (I/R), there is a persistent systemic increase in Th17 cells with potential effects on pulmonary structure and function. Renal I/R injury was performed on rats, and CKD progression was hastened by unilateral nephrectomy and exposure to 4.0% sodium diet between 35 and 63 days post-I/R. Th17 cells in peripheral blood showed a progressive increase up to 63 days after recovery from I/R injury. Infiltration of leukocytes including Th17 cells was also elevated in bronchiolar lavage (BAL) fluid 7 days after I/R and remained elevated for up to 63 days. Lung histology demonstrated an increase in alveolar cellularity and a significant increase in picrosirius red staining. Suppression of lymphocytes with mycophenolate mofetil (MMF) or an IL-17 antagonist significantly reduced Th17 cell infiltration and fibrosis in lung. In addition, tracheal smooth muscle contraction to acetylcholine was significantly enhanced 63-days after I/R relative to sham-operated controls. These data suggest that AKI is associated with a persistent increase in circulating and lung Th17 cells which may promote pulmonary fibrosis and the potential alteration in airway contractility.

IL-17 in the lung: the good, the bad, and the ugly

The IL-17 family of cytokines has emerged over the last two decades as a pleiotropic group of molecules that function in a wide variety of both beneficial and detrimental (pathological) processes, mainly in mucosal barrier tissue. The beneficial effects of IL-17 expression are especially important in the lung, where exposure to foreign agents is abundant. IL-17A plays an important role in protection from both extracellular bacteria and fungi, as well as viruses that infect cells of the mucosal tracts. IL-17 coregulated cytokines, such as IL-22, are involved in maintaining epithelial cell homeostasis and participate in epithelial cell repair/regeneration following inflammatory insults. Thus, the IL-17/IL-22 axis is important in both responding to, and recovering from, pathogens. However, aberrant expression or overexpression of IL-17 cytokines contributes to a number of pathological outcomes, including asthma, pneumonitis, and generation or exacerbation of pulmonary fibrosis. This review covers the good, bad, and ugly aspects of IL-17 in the lung.

Deletion of mTORC1 Activity in CD4+ T Cells Is Associated with Lung Fibrosis and Increased γδ T Cells

Pulmonary fibrosis is a devastating, incurable disease in which chronic inflammation and dysregulated, excessive wound healing lead to progressive fibrosis, lung dysfunction, and ultimately death. Prior studies have implicated the cytokine IL-17A and Th17 cells in promoting the development of fibrosis. We hypothesized that loss of Th17 cells via CD4-specific deletion of mTORC1 activity would abrogate the development of bleomycin-induced pulmonary fibrosis. However, in actuality loss of Th17 cells led to increased mortality and fibrosis in response to bleomycin. We found that in the absence of Th17 cells, there was continued production of IL-17A by γδ T cells. These IL-17A+ γδ T cells were associated with increased lung neutrophils and M2 macrophages, accelerated development of fibrosis, and increased mortality. These data elucidate the critical role of IL-17A+ γδ T cells in promoting chronic inflammation and fibrosis, and reveal a novel therapeutic target for treatment of pulmonary fibrosis.