A novel model of rheumatoid arthritis-associated interstitial lung disease in SKG mice

Card9/neutrophil signalling axis promotes IL-17A-mediated ankylosing spondylitis

OBJECTIVE

Polymorphisms in the antifungal signalling molecule CARD9 are associated with ankylosing spondylitis (AS). Here, we investigated the cellular mechanism by which CARD9 controls pathogenic Th17 responses and the onset of disease in both experimental murine AS and patients.

METHODS

Experiments in SKG, Card9-/-SKG, neutrophil-deplete SKG mice along with in vitro murine, neutrophil and CD4+ T cell cocultures examined Card9 function in neutrophil activation, Th17 induction and arthritis in experimental AS. In AS patients the neutrophil: Bath Ankylosing Spondylitis Functional Index relationship was analysed. In vitro studies with autologous neutrophil: T cell cocultures examined endogenous CARD9 versus the AS-associated variant (rs4075515) of CARD9 in T cellular production of IL-17A.

RESULTS

Card9 functioned downstream of Dectin-1 and was essential for induction of Th17 cells, arthritis and spondylitis in SKG mice. Card9 expression within T cells was dispensable for arthritis onset in SKG mice. Rather, Card9 expression controlled neutrophil function; and neutrophils in turn, were responsible for triggering Th17 expansion and disease in SKG mice. Mechanistically, cocultures of zymosan prestimulated neutrophils and SKG T cells revealed a direct cellular function for Card9 within neutrophils in the potentiation of IL-17 production by CD4+ T cells on TCR-ligation. The clinical relevance of the neutrophil-Card9-coupled mechanism in Th17-mediated disease is supported by a similar observation in AS patients. Neutrophils from HLA-B27+ AS patients expanded autologous Th17 cells in vitro, and the AS-associated CARD9S12N variant increased IL-17A.

CONCLUSIONS

These data reveal a novel neutrophil-intrinsic role for Card9 in arthritogenic Th17 responses and AS pathogenesis. These data provide valuable utility in our future understanding of CARD9-specific mechanisms in spondyloarthritis .

Dysregulation of B lymphocyte development in the SKG mouse model of rheumatoid arthritis

Rheumatoid arthritis is a chronic and systemic inflammatory disease that affects approximately 1% of the world's population and is characterised by joint inflammation, the destruction of articular cartilage and bone, and many potentially life-threatening extraarticular manifestations. B lymphocytes play a central role in the pathology of rheumatoid arthritis as the precursors of autoantibody secreting plasma cells, as highly potent antigen-presenting cells, and as a source of various inflammatory cytokines, however, the effects of rheumatoid arthritis on B lymphocyte development remain poorly understood. Here, we analyse B lymphocyte development in murine models of rheumatoid arthritis, quantifying all the subsets of B cell precursors in the bone marrow and splenic B cells using flow cytometry. We demonstrate a severe reduction in pre-B cells and immature B cells in the bone marrow of mice with active disease, despite no major effects on the mature naïve B cell numbers. The loss of B cell precursors in the bone marrow of the affected mice was associated with a highly significant reduction in the proportion of Ki67+ cells, indicating impaired cell proliferation, while the viability of the B cell precursors was not significantly affected. We also observed some mobilisation of the B cell precursor cells into the mouse spleen, demonstrated with flow cytometry and pre-B colony forming units assays. In summary, the current work demonstrates a severe dysregulation in B lymphocyte development in murine rheumatoid arthritis, with possible implications for B cell repertoire formation, tolerance induction, and disease mechanisms.

Stattic alleviates pulmonary fibrosis in a mouse model of rheumatoid arthritis-relevant interstitial lung disease

Approximately 20% of rheumatoid arthritis (RA) patients have RA-related interstitial lung disease (RA-ILD). Stattic, an STAT3 inhibitor, has been confirmed to be relevant to both RA and ILD. Therefore, this study explored the effect of Stattic on the progression of joint disease and pulmonary fibrosis in zymosan-treated female SKG mice, an established model for autoimmune arthritis. The experimental mice developed pulmonary interstitial pneumonia, which is similar to human cellular and fibrotic nonspecific interstitial pneumonia. Oral gavage of Stattic (60 mg/kg/d) was initiated 10 weeks after zymosan injection. Arthritis and lung fibrosis outcome scores decreased significantly following Stattic treatment. An obvious decrease in lung collagen levels, measured using hydroxyproline level determination and collagen staining, was detected after 6 weeks in Stattic-exposed mice with established disease. Stattic also dramatically restricted arthritis progression, based on joint evaluation. Transforming growth factor beta 1 (TGF-β1) is a pivotal fibrosis-causing cytokine, used here to treat myofibroblasts, thereby establishing a lung fibrosis cell model. Stattic treatment can mitigate the TGF-β1-triggered inflammatory response, myofibroblast activation, oxidative stress, and hyperproliferation by modulating the JAK1/STAT3 pathway. Our observations support a direct role of Stattic-inhibited STAT3 activation in lung fibrosis, which may be particularly relevant in the RA-ILD context.

Interstitial lung disease in rheumatoid arthritis: A multidisciplinary problem in rheumatology and pulmonology

Rheumatoid arthritis (RA) is an immune-mediated rheumatic disease (IMRDs) characterized by chronic erosive arthritis and systemic damage to internal organs, leading to early disability and reduced life expectancy in patients. A particularly important place among the systemic manifestations of RA is occupied by interstitial lung diseases (ILD) – the most severe form of pulmonary pathology in RA, defined as RA-ILD, which is pathogenetically associated with risk factors (smoking, etc.) and autoimmune mechanisms underlying RA. RA-ILD is a subtype of RA characterized by a severe course and a poor prognosis и неблагоприятным прогнозом. The review presents new data regarding risk factors and biomarkers for RA-ILD; modern diagnostic capabilities based on the use of functional lung tests, high-resolution computed tomography, ultrasound examination of the lungs. Particular attention is paid to the efficacy and safety of pharmacotherapy, including methotrexate, biologics, JAK inhibitors, and antifibrotic therapy. An algorithm for the pharmacotherapy of RA-ILD has been proposed.

Engineering Hybrid-Hydrogels Comprised of Healthy or Diseased Decellularized Extracellular Matrix to Study Pulmonary Fibrosis

Idiopathic pulmonary fibrosis is a chronic disease characterized by progressive lung scarring that inhibits gas exchange. Evidence suggests fibroblast-matrix interactions are a prominent driver of disease. However, available preclinical models limit our ability to study these interactions. We present a technique for synthesizing phototunable poly(ethylene glycol) (PEG)-based hybrid-hydrogels comprising healthy or fibrotic decellularized extracellular matrix (dECM) to decouple mechanical properties from composition and elucidate their roles in fibroblast activation. Here, we engineered and characterized phototunable hybrid-hydrogels using molecular techniques such as ninhydrin and Ellman's assays to assess dECM functionalization, and parallel-plate rheology to measure hydrogel mechanical properties. These biomaterials were employed to investigate the activation of fibroblasts from dual-transgenic Col1a1-GFP and αSMA-RFP reporter mice in response to changes in composition and mechanical properties. We show that reacting functionalized dECM from healthy or bleomycin-injured mouse lungs with PEG alpha-methacrylate (αMA) in an off-stoichiometry Michael-addition reaction created soft hydrogels mimicking a healthy lung elastic modulus (4.99 ± 0.98 kPa). Photoinitiated stiffening increased the material modulus to fibrotic values (11.48 ± 1.80 kPa). Percent activation of primary murine fibroblasts expressing Col1a1 and αSMA increased by approximately 40% following dynamic stiffening of both healthy and bleomycin hybrid-hydrogels. There were no significant differences between fibroblast activation on stiffened healthy versus stiffened bleomycin-injured hybrid-hydrogels. Phototunable hybrid-hydrogels provide an important platform for probing cell-matrix interactions and developing a deeper understanding of fibrotic activation in pulmonary fibrosis. Our results suggest that mechanical properties are a more significant contributor to fibroblast activation than biochemical composition within the scope of the hybrid-hydrogel platform evaluated in this study.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12195-022-00726-y.

Huangqi Guizhi Wuwu Decoction Improves Arthritis and Pathological Damage of Heart and Lung in TNF-Tg Mice

Background: Huangqi Guizhi Wuwu Decoction (HGWD) is a traditional and effective Chinese medicine compound decoction for the treatment of rheumatoid arthritis (RA). However, there is few research on the treatment of rheumatoid cardiopulmonary complications. The present study was to study whether HGWD can alleviate the pathological changes caused by rheumatoid arthritis and cardiopulmonary complications.

Methods: Five 3-month-old TNF-Tg mice were treated with HGWD (9.1 g/kg) once a day or the same dose of normal saline lasted for 8 weeks, and wild-type littermates of the same age were used as a negative control, and methotrexate (MTX) was intraperitoneally administered as a positive control. After the treatment, pathological staining was performed on the mouse ankle joints, heart, and lungs.

Result: It was found that HGWD reduced the inflammation of the ankle joint synovium in TNF-Tg mice, and reduced myocardial hypertrophy, inflammatory infiltration and fibrosis of heart, as well as lung inflammation and fibrosis. Immunohistochemical staining with anti-TNF-α antibody showed that HGWD reduced the expression of TNF-α in the heart of TNF-Tg mice.

Conclusion: In conclusion, HGWD alleviates joint inflammation in TNF-Tg mice and reduces the pathological changes of the heart and lungs.

Recent Advances in Basic and Clinical Aspects of Rheumatoid Arthritis-associated Interstitial Lung Diseases

Rheumatoid arthritis (RA) is a common autoimmune disease that mainly affects the joints and systemic organs, such as the skin, eyes, heart, gastrointestinal tract, and lungs. In particular, among various pulmonary involvements, interstitial lung disease (ILD) is closely related to the selection of anti-rheumatic drugs and the long-term prognosis of patients with RA. Although the exact pathogenesis of RA-ILD is not well defined, several mechanistic pathways, similar to those of idiopathic pulmonary fibrosis, have been elucidated recently. Conversely, RA-related autoantibodies, including anti-cyclic citrullinated peptide antibody, are detectable in circulation and in the lungs, even in the absence of articular symptoms. RA-ILD can also predate years before the occurrence of joint symptoms. This evidence supports the fact that local dysregulated mucosal immunity in the lung causes systemic autoimmunity, resulting in clinically evident polyarthritis of RA. Because the early diagnosis of RA-ILD is important, imaging tests, such as computed tomography and pulmonary function tests, are being used for early diagnosis, but there is no clear guideline for the early diagnosis of RA-ILD and selection of optimal disease-modifying anti-rheumatic drugs for the treatment of patients with RA with ILD. In addition, the efficacy of nintedanib, a new anti-fibrotic agent, for RA-ILD treatment, has been investigated recently. This review collectively discusses the basic and clinical aspects, such as pathogenesis, animal models, diagnosis, and treatment, of RA-ILD.

The role of antifibrotics in the treatment of rheumatoid arthritis–associated interstitial lung disease

The major pulmonary complication of rheumatoid arthritis (RA) is interstitial lung disease (ILD), which causes significant morbidity and mortality and influences the natural course of disease. Recent advances in the management of arthritis have improved patient outcomes. However, exceptionally high medical needs still remain for effective therapies for the patients with ILD in RA. Better understanding of the shared and distinct pathophysiology of fibrotic diseases led to the development of novel antifibrotic agents such as nintedanib and pirfenidone. The further stratification analysis of the phase III INBUILD trial demonstrated beneficial effects of nintedanib in RA-ILD with a progressive phenotype by reducing the rate of decline in forced vital capacity (FVC) over 52 weeks by 60%. Pirfenidone is another antifibrotic agent currently under phase II clinical study (TRAIL1) aiming to evaluate its effects for RA-ILD. This review provides an overview of state-of-the-art pathogenesis and the current therapeutic options for RA-ILD, with a focus on antifibrotic strategies.

Suppression of epithelial abnormalities by nintedanib in induced-rheumatoid arthritis-associated interstitial lung disease mouse model

Rheumatoid arthritis-associated interstitial lung disease (RA-ILD) is relevant for the prognosis in patients with RA. Nintedanib, which inhibits both receptor and non-receptor type tyrosine kinases, is an antifibrotic drug for the treatment of progressive fibrosing ILDs, such as idiopathic pulmonary fibrosis and systemic sclerosis-associated interstitial lung disease. Little is known about the effects of nintedanib on RA-ILD. We examined the characteristics of a novel induced RA-ILD (iRA-ILD) mouse model and the effects of nintedanib on the model. D1CC×D1BC mice are highly susceptible to arthritogenic antigens, such as bovine type II collagen, resulting in severe inflammatory arthritis. ILD develops after joint inflammation is alleviated. Serum surfactant protein D levels were monitored as an ILD marker. Nintedanib was orally administered to iRA-ILD mice for 2 months. The iRA-ILD model showed similar symptoms to those in patients with RA-ILD. The histopathological features of pulmonary disorder resembled nonspecific interstitial pneumonia, but with metaplastic epithelium. Histopathological analysis revealed that in addition to reducing fibrosis, nintedanib suppressed M2 macrophage polarisation and hyperplasia of Type 2 alveolar epithelial cells. The metaplastic epithelium acquired invasiveness because of the expression of E-cadherin, MMP7, Tgf-β, Col1a1, Padi2 and Padi4. Moreover, citrullinated peptides were detected in these invasive epithelial cells as well as in the bronchiolar epithelium. Administration of nintedanib reduced the expression of Pad4 and citrullinated peptides and eliminated invasive epithelial cells. The broad inhibitory effects of nintedanib on tyrosine kinases may contribute to the overall improvement in RA-ILD, including epithelial abnormalities associated with progressive lung fibrosis.

Citrullinated fibrinogen is a target of auto-antibodies in interstitial lung disease in mice with collagen-induced arthritis

Interstitial lung disease (ILD) is a very common and lethal complication of rheumatoid arthritis (RA), yet its pathogenesis is not well understood, in part due to the lack of adequate animal models. Although collagen-induced arthritis (CIA) is the most widely used animal model for RA, the lung involvement occurring in this model has scarcely been studied. To evaluate the suitability of CIA as a model for RA-associated ILD (RA-ILD), we immunized DBA/1 mice with bovine type II collagen and characterized lung disease in this model. Histologic analyses revealed patchy interstitial infiltration of inflammatory cells in the peripheral regions of the lung, notably in the subpleural region, in mice with CIA. This pattern resembled usual interstitial pneumonia in humans, which is the most prevalent pattern in RA-ILD. Among infiltrates in the lung, CD11bhi macrophages of the M2 phenotype were most prominently increased. IgG and C3 were deposited in the subpleural region where inflammatory cells infiltrated. The sera from CIA mice contained auto-antibodies against citrullinated proteins, which are specific and predictive markers for RA. Protein citrullination was enhanced in the lung of CIA mice compared with naive mice, and citrullinated fibrinogen was primarily targeted by these auto-antibodies. The elevation of auto-antibodies against citrullinated proteins and their deposition in the lung with patchy subpleural preponderance suggest that CIA can serve as a model to study the pathogenesis of RA-ILD.

A novel humanized model of rheumatoid arthritis associated lung disease

Cigarette smoking has been implicated in the pathogenesis of seropositive rheumatoid arthritis (RA), as well as RA-associated lung disease. Fibrotic interstitial lung disease as well as emphysema occur in RA and cause substantial morbidity. We used arthritis-susceptible HLA-DQ8 transgenic mice to generate RA-associated lung disease. Mice were exposed to cigarette smoke (CS) prior to induction of arthritis, and subsequently injected with a low dose of bleomycin intra-tracheally to induce lung injury. Exposure of arthritic mice to both CS and bleomycin led to a significant reduction in lung compliance consistent with development of diffuse lung disease. Morphologic evaluation of the lung demonstrated areas of emphysematous change and co-existent fibrosis, consistent with a combined pattern of fibrosis and emphysema. These changes were accompanied by inflammatory cell infiltration and upregulation of fibrosis-associated genes. This humanized mouse model can serve as a valuable research tool to understand the pathogenesis of RA associated lung disease.

High-throughput analysis of lung immune cells in a combined murine model of agriculture dust-triggered airway inflammation with rheumatoid arthritis

Rheumatoid arthritis (RA)-associated lung disease is a leading cause of mortality in RA, yet the mechanisms linking lung disease and RA remain unknown. Using an established murine model of RA-associated lung disease combining collagen-induced arthritis (CIA) with organic dust extract (ODE)-induced airway inflammation, differences among lung immune cell populations were analyzed by single cell RNA-sequencing. Additionally, four lung myeloid-derived immune cell populations including macrophages, monocytes/macrophages, monocytes, and neutrophils were isolated by fluorescence cell sorting and gene expression was determined by NanoString analysis. Unsupervised clustering revealed 14 discrete clusters among Sham, CIA, ODE, and CIA+ODE treatment groups: 3 neutrophils (inflammatory, resident/transitional, autoreactive/suppressor), 5 macrophages (airspace, differentiating/recruited, recruited, resident/interstitial, and proliferative airspace), 2 T-cells (differentiating and effector), and a single cluster each of inflammatory monocytes, dendritic cells, B-cells and natural killer cells. Inflammatory monocytes, autoreactive/suppressor neutrophils, and recruited/differentiating macrophages were predominant with arthritis induction (CIA and CIA+ODE). By specific lung cell isolation, several interferon-related and autoimmune genes were disproportionately expressed among CIA and CIA+ODE (e.g. Oasl1, Oas2, Ifit3, Gbp2, Ifi44, and Zbp1), corresponding to RA and RA-associated lung disease. Monocytic myeloid-derived suppressor cells were reduced, while complement genes (e.g. C1s1 and Cfb) were uniquely increased in CIA+ODE mice across cell populations. Recruited and inflammatory macrophages/monocytes and neutrophils expressing interferon-, autoimmune-, and complement-related genes might contribute towards pro-fibrotic inflammatory lung responses following airborne biohazard exposures in setting of autoimmune arthritis and could be predictive and/or targeted to reduce disease burden.

Animal models of rheumatoid arthritis-associated interstitial lung disease

BACKGROUND

Rheumatoid arthritis-associated interstitial lung disease (RA-ILD) is an irreversible pathologic condition of unknown cause, commonly involving the joint and the lung with variable amounts of fibrotic change. In contrast to rheumatoid arthritis or other chronic interstitial lung diseases such as interstitial pulmonary fibrosis, there is so far no extensively accepted or implemented animal model for this disease.

AIMS

To provide guidance for those who are investigating the pathogenesis of RA-ILD with animal models.

MATERIALS AND METHODS

An analysis of papers from PubMed during 1978-2020.

RESULTS

We outline the present status quo for animal models of RA-ILD about their modeling methods and pathogenesis, compare their pros and cons with respect to their ability to mimic the clinical and histological features of human disease and discuss their applicability for future research.

DISCUSSION

There is no doubt that these animal models do provide valuable information relating to the pathogenesis of RA-ILD and the development of effective therapeutic drugs. Nevertheless, these animal models can not entirely recapitulate clinical pathology and have some limitations in experimental research application. Therefore, it should be emphasized that we should improve and explore animal models in more accordance with the pathogenesis and clinical characteristics of human RA-ILD.

CONCLUSION

These established animal models of the disease can significantly progress our understanding of the etiology of RA-ILD, the fundamental mechanisms of its pathogenesis and the identification of new bio-markers, and can contribute to the development and implementation of novel treatment strategies.

Reinterpreting Evidence of Rheumatoid Arthritis-Associated Interstitial Lung Disease to Understand Etiology

Interstitial Lung Disease (ILD) is a well-known complication of rheumatoid arthritis (RA) which often results in significant morbidity and mortality. It is often diagnosed late in the disease process via descriptive criteria. Multiple subtypes of RA-ILD exist as defined by chest CT and histopathology. In the absence of formal natural history studies and definitive diagnostics, a conventional dogma has emerged that there are two major subtypes of RA-ILD (nonspecific interstitial pneumonia (NSIP) and Usual Interstitial Pneumonia (UIP)). These subtypes are based on clinical experience and correlation studies. However, recent animal model data are incongruous with established paradigms of RA-ILD and beg reassessment of the clinical evidence in order to better understand etiology, pathogenesis, prognosis, and response to therapy. To this end, here we: 1) review the literature on epidemiology, radiology, histopathology and clinical outcomes of the various RAILD subtypes, existing animal models, and current theories on RA-ILD pathogenesis; 2) highlight the major gaps in our knowledge; and 3) propose future research to test an emerging theory of RAILD that posits initial rheumatic lung inflammation in the form of NSIP-like pathology transforms mesenchymal cells to derive chimeric disease, and subsequently develops into frank UIP-like fibrosis in some RA patients. Elucidation of the pathogenesis of RA-ILD is critical for the development of effective interventions for RA-ILD.

Combined Collagen-Induced Arthritis and Organic Dust-Induced Airway Inflammation to Model Inflammatory Lung Disease in Rheumatoid Arthritis

Rheumatoid arthritis (RA) is characterized by extra-articular involvement including lung disease, yet the mechanisms linking the two conditions are poorly understood. The collagen-induced arthritis (CIA) model was combined with the organic dust extract (ODE) airway inflammatory model to assess bone/joint-lung inflammatory outcomes. DBA/1J mice were intranasally treated with saline or ODE daily for 5 weeks. CIA was induced on days 1 and 21. Treatment groups included sham (saline injection/saline inhalation), CIA (CIA/saline), ODE (saline/ODE), and CIA +  ODE (CIA/ODE). Arthritis inflammatory scores, bones, bronchoalveolar lavage fluid, lung tissues, and serum were assessed. In DBA/1J male mice, arthritis was increased in CIA +  ODE >  CIA >  ODE versus sham. Micro-computed tomography (µCT) demonstrated that loss of BMD and volume and deterioration of bone microarchitecture was greatest in CIA +  ODE. However, ODE-induced airway neutrophil influx and inflammatory cytokine/chemokine levels in lavage fluids were increased in ODE >  CIA +  ODE versus sham. Activated lung CD11c+ CD11b+ macrophages were increased in ODE >  CIA +  ODE >  CIA pattern, whereas lung hyaluronan, fibronectin, and amphiregulin levels were greatest in CIA +  ODE. Serum autoantibody and inflammatory marker concentrations varied among experimental groups. Compared with male mice, female mice showed less articular and pulmonary disease. The interaction of inhalation-induced airway inflammation and arthritis induction resulted in compartmentalized responses with the greatest degree of arthritis and bone loss in male mice with combined exposures. Data also support suppression of the lung inflammatory response, but increases in extracellular matrix protein deposition/interstitial disease in the setting of arthritis. This coexposure model could be exploited to better understand and treat RA-lung disease. © 2019 American Society for Bone and Mineral Research.

Restrictive lung disease in TNF-transgenic mice: correlation of pulmonary function testing and micro-CT imaging

Purpose: Micro-computed tomography (µCT) is increasingly being used on animal models as a minimally-invasive longitudinal outcome measure of pulmonary disease progression. However, while imaging can elucidate macroscopic structural changes over the whole lung, µCT is unable to describe the mechanical changes and functional impairments imposed by progressive disease, which can only be measured via pulmonary function tests (PFTs). The tumor necrosis factor-transgenic (TNF-Tg) mouse model of rheumatoid arthritis (RA) develops pulmonary pathology that mimics many aspects of the inflammatory interstitial lung disease (ILD) seen in a subset of patients with RA. Prior studies using µCT imaging of these mice found increased pulmonary density, characteristic of restrictive disease; however, there have been conflicting reports in the literature regarding the obstructive versus restrictive phenotype of this model. Our study looks to 1) define the functional impairments and 2) characterize the restrictive/obstructive nature of the disease found in this model. Materials and Methods: In this study, we performed PFTs at end-stage ILD, and paired these findings with µCT results, correlating radiology to functional parameters. TNF-Tg and WT littermates of both sexes underwent µCT imaging and PFT testing at 5.5 months-old. Spearman's correlation analyses were performed comparing lung tissue volume (LTV) to PFT parameters of gas exchange and tissue stiffness. Results: Compared to WT, TNF-Tg mice had impaired gas exchange capacity, increased respiratory resistance, and reduced lung compliance, elastance, and inspiratory capacity, indicating increased tissue stiffness and compromised pulmonary function. LTV was also consistently higher in TNF-Tg lungs. Conclusions: These findings demonstrate that: 1) TNF-Tg mice display a restrictive pathology, and 2) in vivo µCT is a valid outcome measure to infer changes in pulmonary mechanical and functional parameters.

Nintedanib reduces pulmonary fibrosis in a model of rheumatoid arthritis-associated interstitial lung disease

Rheumatoid arthritis (RA)-associated interstitial lung disease (RA-ILD) develops in ~20% of patients with RA. SKG mice, which are genetically prone to development of autoimmune arthritis, develop a pulmonary interstitial pneumonia that resembles human cellular and fibrotic nonspecific interstitial pneumonia. Nintedanib, a tyrosine kinase inhibitor approved for treatment of idiopathic pulmonary fibrosis, has been shown to reduce the decline in lung function. Therefore, we investigated the effect of nintedanib on development of pulmonary fibrosis and joint disease in female SKG mice with arthritis induced by intraperitoneal injection of zymosan (5 mg). Nintedanib (60 mg·kg-1·day-1 via oral gavage) was started 5 or 10 wk after injection of zymosan. Arthritis and lung fibrosis outcome measures were assessed after 6 wk of treatment with nintedanib. A significant reduction in lung collagen levels, determined by measuring hydroxyproline levels and staining for collagen, was observed after 6 wk in nintedanib-treated mice with established arthritis and lung disease. Early intervention with nintedanib significantly reduced development of arthritis based on joint assessment and high-resolution μ-CT. This study impacts the RA and ILD fields by facilitating identification of a therapeutic treatment that may improve both diseases. As this model replicates the characteristics of RA-ILD, the results may be translatable to the human disease.

The Role of Flavonoids in Inhibiting Th17 Responses in Inflammatory Arthritis

Flavonoids have been considered powerful anti-inflammatory agents, and their exact immunomodulatory action as therapeutic agents in autoimmune diseases has started to emerge. Their role in the manipulation of immunoregulation is less understood. Several studies attempted to investigate the role of various flavonoids mainly in experimental models of autoimmune diseases, especially in the context of their potential effect on the increase of regulatory T cells (Tregs) and their ability to stimulate an overexpression of anti-inflammatory cytokines, in particular that of IL-10. The emergence of IL-17, a cytokine largely produced by Th17 cells, as a powerful proinflammatory stimulus which attenuates the induction of Tregs has prompted a series of studies investigating the role of flavonoids on Th17 cells in experimental models as well as human autoimmune diseases. This review thoroughly discusses accumulated data on the role of flavonoids on Th17 in rheumatoid arthritis and experimental autoimmune arthritis.

Reduced Numbers of Mature Medullary Thymic Epithelial Cells in SKG Mice

Attenuated T cell receptor (TCR) signalling contributes to the susceptibility for autoimmunity as shown via mutants of PTPN22 and Zap70 genes. We here set out to investigate the effect of an attenuated TCR signal on the composition of the thymic epithelial cell (TEC) compartment. To that extent, we combined flow cytometry and histology and compared the TEC subpopulations of Zap70 wild type with SKG mutant mice. We found an increased cortical TEC compartment in SKG thymi at the expense of reduced numbers of mature medullary TECs and a 4.8-fold reduced medulla area. We also found reduced proportions of CD69⁺ -activated thymocytes among double-negative, double-positive and CD4^- CD8⁺ single-positive stages, reduced absolute numbers of single-positive thymocytes, diminished expression of Lta and Ltb by CD4^- CD8⁺ single-positive thymocytes and a diminished expression of Ccl19, a target gene of the lymphotoxin-b-receptor. While the reduced thymocyte numbers together with the attenuated TCR signal explain the diminished expression of lymphotoxins, the latter is required for an AIRE-independent expression of tissue-restricted antigens as well as attracting positively selected thymocytes to the medulla. Our results describe altered TEC compartments in SKG mice that are likely to support the development of autoimmunity.

Expression of CCR3, SOX5 and LC3 in patients with elderly onset rheumatoid arthritis and the clinical significance

This study investigated the expression of C-C chemokine receptor type 3 (CCR3), transcription factor SOX5 (SOX5) and microtubule-associated protein 1 light chain 3 (LC3) in patients with elderly onset rheumatoid arthritis (EORA) and the clinical significance. Ninety patients with elderly onset rheumatoid arthritis were selected in our hospital from January to December in 2016 to serve as patient group. At the same time, 50 healthy people were selected as control group. Levels of CCR3, SOX5 and LC3 in serum of two groups were detected by enzyme-linked immunosorbent assay (ELISA). Expression levels of CCR3, SOX5 and LC3 mRNA in peripheral blood mononuclear cells (PBMCs) were detected by reverse transcription-PCR (RT-PCR). Expression level of CCR3 mRNA in patient group was 0.752±0.054, which was significantly higher than that in control group (0.287±0.032, t=8.932, P<0.05). Levels of CCR3, SOX5 and LC3 in serum of patients in patient group were significantly higher than those in control group (P<0.05). Positive correlations were found between serum levels of CCR3 and SOX5 (r=0.613, P<0.05), serum levels of CCR3 and LC3 (r=0.637, P<0.05), and serum levels of SOX5 and LC3 (r=0.645, P<0.05). CCR3, SOX5 and LC3 are highly expressed in PBMC and serum, which may be closely related to the occurrence and development of EORA. These indexes may be used as indicators of clinical diagnosis and prognosis of patients with EORA.

Th17 in Animal Models of Rheumatoid Arthritis

IL-17-secreting helper CD4 T cells (Th17 cells) constitute a newly identified subset of helper CD4 T cells that play a key role in the development of rheumatoid arthritis (RA) in its animal models. Recently, several models of spontaneous RA, which elucidate the mechanism of RA onset, have been discovered. These animal models shed new light on the role of Th17 in the development of autoimmune arthritis. Th17 cells coordinate inflammation and promote joint destruction, acting on various cells, including neutrophils, macrophages, synovial fibroblasts, and osteoclasts. Regulatory T cells cannot control Th17 cells under conditions of inflammation. In this review, the pathogenic role of Th17 cells in arthritis development, which was revealed by the recent animal models of RA, is discussed.

Tumor necrosis factor alpha, citrullination, and peptidylarginine deiminase 4 in lung and joint inflammation

Background

The relationship between lung and joint inflammation in rheumatoid arthritis is poorly understood. Lung inflammation with resultant protein citrullination may trigger anti-citrullinated protein antibodies, inflammation, and arthritis. Alternatively, lung and joint inflammation may be two manifestations of a single underlying pathology. The lung has increased citrullination and TNF-α levels are high in rheumatoid arthritis; however, it is unknown if TNF-α can induce lung protein citrullination. The citrullinating enzyme peptidylarginine deiminase 4 (PAD4) exacerbates TNF-α-induced arthritis, but a role for PAD4 in lung citrullination and TNF-α-induced lung inflammation has not been explored. Our aim was to use TNF-α-overexpressing mice to clarify the intersection of TNF-α, citrullination, PAD4, arthritis, and lung inflammation.

Methods

Lung protein citrullination in wild-type mice, mice that overexpress TNF-α systemically (TNF⁺), TNF⁺PAD4^+/+, and TNF⁺PAD4^-/- mice was quantified by both gel electrophoresis using a citrulline probe and western blot. Hematoxylin and eosin (H&E)-stained lung sections from TNF⁺PAD4^+/+ and TNF⁺PAD4^-/- mice were scored for lung inflammation. H&E-stained ankle joint sections from mice that overexpress TNF-α only in the lungs were assessed for arthritis.

Results

TNF⁺ mice have increased lung protein citrullination. TNF⁺PAD4^-/- mice do not have significantly reduced lung protein citrullination, but do have decreased lung inflammation compared to TNF⁺PAD4^+/+ mice. Mice that overexpress TNF-α only in the lungs do not develop arthritis.

Conclusions

PAD4 exacerbates lung inflammation downstream of TNF-α without having a major role in generalized protein citrullination in inflamed lungs. Also, TNF-α-induced lung inflammation is not sufficient to drive murine arthritis.

Electronic supplementary material

The online version of this article (doi:10.1186/s13075-016-1068-0) contains supplementary material, which is available to authorized users.

GM-CSF as a therapeutic target in autoimmune diseases

Granulocyte-macrophage colony-stimulating factor (GM-CSF) has been known as a hematopoietic growth factor and immune modulator. Recent studies revealed that GM-CSF also had pro-inflammatory functions and contributed to the pathogenicity of Th17 cells in the development of Th17-mediated autoimmune diseases. GM-CSF inhibition in some animal models of autoimmune diseases showed significant beneficial effects. Therefore, several agents targeting GM-CSF are being developed and are expected to be a useful strategy for the treatment of autoimmune diseases. Particularly, in clinical trials for rheumatoid arthritis (RA) patients, GM-CSF inhibition showed rapid and significant efficacy with no serious side effects. This article summarizes recent findings of GM-CSF and information of clinical trials targeting GM-CSF in autoimmune diseases.

Differential innate immune cell signatures and effects regulated by toll-like receptor 4 during murine lung tumor promotion

Tumor promotion is an early and critical stage during lung adenocarcinoma (ADC). We previously demonstrated that Tlr4 mutant mice were more susceptible to butylated hydroxytoluene (BHT)-induced pulmonary inflammation and tumor promotion in comparison to Tlr4-sufficient mice. Our study objective was to elucidate the underlying differences in Tlr4 mutant mice in innate immune cell populations, their functional responses, and the influence of these cellular differences on ADC progenitor (type II) cells following BHT-treatment. BALB (Tlr4-sufficient) and C.C3-Tlr4(Lps-d)/J (BALB(Lpsd); Tlr4 mutant) mice were treated with BHT (promoter) followed by bronchoalveolar lavage (BAL) and flow cytometry processing on the lungs. ELISAs, Club cell enrichment, macrophage function, and RNA isolation were also performed. Bone marrow-derived macrophages (BMDM) co-cultured with a type II cell line were used for wound healing assays. Innate immune cells significantly increased in whole lung in BHT-treated BALB(Lpsd) mice compared to BALB mice. BHT-treated BALB(Lpsd) mice demonstrated enhanced macrophage functionality, increased epithelial wound closure via BMDMs, and increased Club cell number in BALB(Lpsd) mice, all compared to BALB BHT-treated mice. Cytokine/chemokine (Kc, Mcp1) and growth factor (Igf1) levels also significantly differed among the strains and within macrophages, gene expression, and cell surface markers collectively demonstrated a more plastic phenotype in BALB(Lpsd) mice. Therefore, these correlative studies suggest that distinct innate immune cell populations are associated with the differences observed in the Tlr4-mutant model. Future studies will investigate the macrophage origins and the utility of the pathways identified herein as indicators of immune system deficiencies and lung tumorigenesis.

Chronic graft-versus-host-disease in CD34(+)-humanized NSG mice is associated with human susceptibility HLA haplotypes for autoimmune disease

Chronic graft-versus-host disease (cGVHD) is a significant hurdle to long-term hematopoietic stem-cell transplantation success. Insights into the pathogenesis and mechanistical investigations of novel therapeutic strategies are limited as appropriate animal models are missing. The immunodeficient NSG mouse - when humanized with human bone marrow, fetal liver and thymus (BLT NSG) - is prone for cGVHD, yet mainly affects the skin. In contrast, the NSG mouse humanized exclusively with CD34(+)-selected, CD3(+)-depleted stem cells (CD34(+)NSG) has neither been described for acute nor chronic GVHD so far. This is the first report about the development of systemic autoimmune cGVHD ≥24 weeks post stem cell receipt involving lung, liver, skin, gingiva and intestine in two NSG cohorts humanized with CD34(+) grafts from different donors. Affected mice presented with sclerodermatous skin, fibrotic lung, severe hepatitis, and massive dental malformation/loss. CD4(+)-dominated, TH2-biased, bulky T-cell infiltrates featured highly skewed T cell receptor (TCR) repertoires, clonal expansions, and autoreactive TCRs. In affected tissues profibrotic IL-13 and -4 dominated over TH1 cytokines IFN-γ and TNF-α. Thus, the time point of manifestation and the phenotype match human systemic pleiotropic sclerodermatous GVHD. The CD34(+)NSG-model's intrinsic deficiency of thymus, thymus-derived regulatory T cells (nTreg) and B cells emphasizes the role of the genetic polymorphism and the cytokines in the pathogenesis of cGVHD. Importantly, the only factor discriminating diseased versus non-diseased CD34(+)NSG cohorts were two risk HLA haplotypes that in human mediate susceptibility for autoimmune disease (psoriasis). Thus, the CD34(+)NSG model may serve as a platform for addressing issues related to the pathophysiology and treatment of human autoimmunity and chronic GVHD.

Animal models of rheumatoid arthritis: How informative are they?

Animal models of arthritis are widely used to de-convolute disease pathways and to identify novel drug targets and therapeutic approaches. However, the high attrition rates of drugs in Phase II/III rates means that a relatively small number of drugs reach the market, despite showing efficacy in pre-clinical models. There is also increasing awareness of the ethical issues surrounding the use of animal models of disease and it is timely, therefore, to review the relevance and translatability of animal models of arthritis. In this paper we review the most commonly used animal models in terms of their pathological similarities to human rheumatoid arthritis as well as their response to drug therapy. In general, the ability of animal models to predict efficacy of biologics in man has been good. However, the predictive power of animal models for small molecules has been variable, probably because of differences in the levels of target knockdown achievable in vivo.

Pivotal roles of GM-CSF in autoimmunity and inflammation

Granulocyte macrophage-colony stimulating factor (GM-CSF) is a hematopoietic growth factor, which stimulates the proliferation of granulocytes and macrophages from bone marrow precursor cells. In autoimmune and inflammatory diseases, Th17 cells have been considered as strong inducers of tissue inflammation. However, recent evidence indicates that GM-CSF has prominent proinflammatory functions and that this growth factor (not IL-17) is critical for the pathogenicity of CD4⁺ T cells. Therefore, the mechanism of GM-CSF-producing CD4⁺ T cell differentiation and the role of GM-CSF in the development of autoimmune and inflammatory diseases are gaining increasing attention. This review summarizes the latest knowledge of GM-CSF and its relationship with autoimmune and inflammatory diseases. The potential therapies targeting GM-CSF as well as their possible side effects have also been addressed in this review.

A retrospective study of clinical characteristics of interstitial lung disease associated with rheumatoid arthritis in Chinese patients

Background

Interstitial lung disease (ILD) in rheumatoid arthritis (RA) is associated with a poor prognosis. The purpose of this study was to assess the characteristics of ILD that are associated with RA.

Material/Methods

This was a retrospective study of 544 Chinese patients with RA (427 women and 117 men). RA-ILD was diagnosed by high-resolution computed tomography (HRCT). Patients with RA-ILD or with RA alone were compared in terms of age, sex distribution, duration of disease, clinical and laboratory parameters, history of smoking, and medication.

Results

Based on HRCT imaging, 83 (15.26%) patients with RA were diagnosed with ILD. ILD was more frequent in older patients (59.60±9.66 vs. 50.54±13.76 years, P<0.001), in those with a longer duration of disease (7.46±7.40 vs. 5.27±6.32 years, P=0.013) and in male patients (34.9% vs. 19.1%, P=0.001). RA-ILD was found to be associated with hepatitis B surface antigen (HBsAg) positivity (odds ratio [OR]=2.56, 95% confidence interval [95% CI] 1.02–6.43) and smoking (OR=3.38, 95% CI 1.65–6.95). Higher levels of C-reactive protein (OR=3.59, 95% CI 1.58–8.15), anti-cyclic citrullinated peptide (CCP) (OR=2.24, 95% CI 2.09–4.13), and rheumatoid factor (OR=3.72, 95% CI 1.56–8.86) were detected in association with RA-ILD. RA-ILD was more frequently observed in patients treated with steroids (OR=1.91, 95% CI 1.18–3.09) or Tripterygium wilfordii (OR=2.56, 95% CI 1.21–5.40). Age (OR=2.20, 95% CI 1.04–4.65), age at RA onset (OR=2.55, 95% CI 1.11–5.90), anti-CCP (OR=2.47, 95% CI 1.19–5.17), and steroid use (OR=1.83, 95% CI 1.04–3.20) were independently associated with RA-ILD in multivariate analysis.

Conclusions

RA-ILD was associated with age, age at RA onset, anti-CCP, and steroid use. Anti-CCP antibodies might be important biomarkers of RA-ILD.

GM-CSF but not IL-17 is critical for the development of severe interstitial lung disease in SKG mice

Interstitial lung disease (ILD) is a common complication and sometimes a prognostic factor of connective tissue diseases (CTDs) in humans. However, suitable animal model of severe CTD-associated ILD (CTD-ILD) has been limited. In this study, we showed that zymosan-treated SKG mice developed not only arthritis but also chronic-progressive ILD with high mortality over several months. The pathological and clinical features of ILD in zymosan-treated SKG mice were similar to that of human severe CTD-ILD. ILD in this mouse was characterized by massive infiltration of Th17 cells, GM-CSF-producing CD4(+) T cells, and CD11b(+) Gr1(+) neutrophils with fibrosis. Naive SKG T cells were skewed to differentiate into GM-CSF-producing cells, and GM-CSF secreted by T cells enhanced IL-6 and IL-1β production by macrophages, which in turn enhanced differentiation of IL-17A- and/or GM-CSF-producing T cells and infiltration of neutrophils into lung. Neutralization of GM-CSF completely blocked the development of this ILD, and the blocking of IL-6 signaling resulted in partial prevention of it, whereas neutralization of IL-17A did not. In contrast, the progression of arthritis was inhibited by the neutralization of GM-CSF and slightly by the neutralization of IL-17A, but not by the blocking of IL-6 signaling. These data suggested zymosan-treated SKG mice could be a useful mouse model of severe CTD-ILD, and GM-CSF, rather than IL-17A or IL-6, contributed to the development of ILD in zymosan-treated SKG mice, indicating that neutralization of GM-CSF would be a useful therapeutic strategy for severe CTD-ILD.

The lung may play a role in the pathogenesis of rheumatoid arthritis

Multiple studies have identified strong associations between the lung and rheumatoid arthritis (RA). Such studies identify a high prevalence of lung disease, both airways and parenchymal disease, in subjects with clinically classifiable RA. It has been suggested that lung disease in RA results from targeting of the lung from circulating autoimmunity or other factors such as medications. However, findings that lung disease, specifically inflammatory airways disease, and lung generation of autoimmunity can be present before the onset of joint symptoms suggest that immune reactions in the lung may be involved in the initial development of RA-related autoimmunity. Herein we review these issues in detail, as well as outline a potential research agenda to understand the natural history of lung involvement in RA and its relation to the overall pathogenesis of RA.

Tumor necrosis factor-α accelerates the resolution of established pulmonary fibrosis in mice by targeting profibrotic lung macrophages

Idiopathic pulmonary fibrosis (IPF) is a relentless, fibrotic parenchymal lung disease in which alternatively programmed macrophages produce profibrotic molecules that promote myofibroblast survival and collagen synthesis. Effective therapies to treat patients with IPF are lacking, and conventional therapy may be harmful. We tested the hypothesis that therapeutic lung delivery of the proinflammatory cytokine tumor necrosis factor (TNF)-α into wild-type fibrotic mice would reduce the profibrotic milieu and accelerate the resolution of established pulmonary fibrosis. Fibrosis was assessed in bleomycin-instilled wild-type and TNF-α(-/-) mice by measuring hydroxyproline levels, static compliance, and Masson's trichrome staining. Macrophage infiltration and programming status was assessed by flow cytometry of enzymatically digested lung and in situ immunostaining. Pulmonary delivery of TNF-α to wild-type mice with established pulmonary fibrosis was found to reduce their fibrotic burden, to improve lung function and architecture, and to reduce the number and programming status of profibrotic alternatively programmed macrophages. In contrast, fibrosis and alternative macrophage programming were prolonged in bleomycin-instilled TNF-α(-/-) mice. To address the role of the reduced numbers of alternatively programmed macrophages in the TNF-α-induced resolution of established pulmonary fibrosis, we conditionally depleted macrophages in MAFIA (MAcrophage Fas-Induced Apoptosis) mice. Conditional macrophage depletion phenocopied the resolution of established pulmonary fibrosis observed after therapeutic TNF-α delivery. Taken together, our results show for the first time that TNF-α is involved in the resolution of established pulmonary fibrosis via a mechanism involving reduced numbers and programming status of profibrotic macrophages. We speculate that pulmonary delivery of TNF-α or augmenting its signaling pathway represent a novel therapeutic strategy to resolve established pulmonary fibrosis.

The multifaceted aspects of interstitial lung disease in rheumatoid arthritis

Interstitial lung disease (ILD) is a relevant extra-articular manifestation of rheumatoid arthritis (RA) that may occur either in early stages or as a complication of long-standing disease. RA related ILD (RA-ILD) significantly influences the quoad vitam prognosis of these patients. Several histopathological patterns of RA-ILD have been described: usual interstitial pneumonia (UIP) is the most frequent one, followed by nonspecific interstitial pneumonia (NSIP); other patterns are less commonly observed. Several factors have been associated with an increased risk of developing RA-ILD. The genetic background plays a fundamental but not sufficient role; smoking is an independent predictor of ILD, and a correlation with the presence of rheumatoid factor and anti-cyclic citrullinated peptide antibodies has also been reported. Moreover, both exnovo occurrence and progression of ILD have been related to drug therapies that are commonly prescribed in RA, such as methotrexate, leflunomide, anti-TNF alpha agents, and rituximab. A greater understanding of the disease process is necessary in order to improve the therapeutic approach to ILD and RA itself and to reduce the burden of this severe extra-articular manifestation.

Enabling hyperpolarized (129) Xe MR spectroscopy and imaging of pulmonary gas transfer to the red blood cells in transgenic mice expressing human hemoglobin

PURPOSE

Hyperpolarized (HP) (129) Xe gas in the alveoli can be detected separately from (129) Xe dissolved in pulmonary barrier tissues (blood plasma and parenchyma) and red blood cells (RBCs) of humans, allowing this isotope to probe impaired gas uptake. Unfortunately, mice, which are favored as lung disease models, do not display a unique RBC resonance, thus limiting the preclinical utility of (129) Xe MR. Here we overcome this limitation using a commercially available strain of transgenic mice that exclusively expresses human hemoglobin.

METHODS

Dynamic HP (129) Xe MR spectroscopy, and three-dimensional radial MRI of gaseous and dissolved (129) Xe were performed in both wild-type (C57BL/6) and transgenic mice.

RESULTS

Unlike wild-type animals, transgenic mice displayed two dissolved (129) Xe NMR peaks at 198 and 217 ppm, corresponding to (129) Xe dissolved in barrier tissues and RBCs, respectively. Moreover, signal from these resonances could be imaged separately, using a 1-point variant of the Dixon technique.

CONCLUSION

It is now possible to examine the dynamics and spatial distribution of pulmonary gas uptake by the RBCs of mice using HP (129) Xe MR spectroscopy and imaging. When combined with ventilation imaging, this ability will enable translational "mouse-to-human" studies of impaired gas exchange in a variety of pulmonary diseases.

Testosterone is protective in the sexually dimorphic development of arthritis and lung disease in SKG mice

OBJECTIVE

Rheumatoid arthritis (RA) is a sexually dimorphic inflammatory autoimmune disease with both articular and extraarticular disease manifestations, including RA-associated interstitial lung disease. Low levels of testosterone have been linked to disease severity in men with RA, and supplemental testosterone has been shown to improve RA symptoms in both postmenopausal women and men with low levels of testosterone. The mechanisms by which sex and sex steroids affect the immune system and autoimmunity are poorly understood. The purpose of this study was to examine the protective effects of testicular-derived sex hormones on the development of joint and lung disease in an autoimmune mouse model.

METHODS

Arthritis prevalence and severity were assessed in orchiectomized, sham-orchiectomized, and intact male SKG mice as well as in female SKG mice over a 12-week period after intraperitoneal injection of zymosan. Lung tissues were evaluated by quantifying cellular accumulation in bronchoalveolar lavage fluid, collagen levels, and histologic changes. An antigen microarray was used to evaluate autoantibody generation under each experimental condition.

RESULTS

Female SKG mice developed arthritis and lung disease at increased prevalence and severity as compared to intact male mice. The absence of testosterone after orchiectomy led to increased arthritis, lung disease, and autoantibody generation in orchiectomized male mice as compared to intact male mice.

CONCLUSION

SKG mice represent an authentic sexually dimorphic mouse model of both the joint and lung disease seen in humans with RA. Testosterone protects against the development of joint and lung disease in male SKG mice.

Autoreactive T and B cells induce the development of bronchus-associated lymphoid tissue in the lung

Rheumatoid arthritis-related interstitial lung disease (RA-ILD) is associated with significant morbidity and mortality. Studies in humans have found that the incidence of bronchus-associated lymphoid tissue (BALT) correlates with the severity of lung injury. However, the mechanisms underlying the development of BALT during systemic autoimmunity remain unknown. We have determined whether systemic autoimmunity in a murine model of autoimmune arthritis can promote the development of BALT by generating a novel murine model derived from K/BxN mice. Transgenic mice with the KRN T-cell receptor specific for the autoantigen, glucose-6-phosphate isomerase (GPI), were crossed with GPI-specific immunoglobulin heavy and light chain knock-in mice, producing mice with a majority of T and B cells specific for the same autoantigen. We found that 67% of these mice demonstrated lymphocytic infiltration in the lungs, localized to either the perivascular or peribronchial regions. Fifty percent of the mice with lymphocytic infiltration manifested lymphoid-like lesions resembling BALT, with distinct T and B cell follicles. The lungs from mice with lymphoid infiltrates had increased numbers of cytokine-producing T cells, including IL-17A(+) T cells and increased major histocompatibility complex Class II expression on B cells. Interestingly, challenge with bleomycin failed to elicit a significant fibrotic response, compared with wild-type control mice. Our data suggest that systemic autoreactivity promotes ectopic lymphoid tissue development in the lung through the cooperation of autoreactive T and B cells. However, these BALT-like lesions may not be sufficient to promote fibrotic lung disease at steady state or after inflammatory challenge.

Chronic inflammation and lung fibrosis: pleotropic syndromes but limited distinct phenotypes

Experimental models of lung fibrosis have been disappointing in predicting therapeutic responses to a wide variety of interventions in clinical fibrosing lung diseases. There are multiple potential reasons, but this fundamentally calls into question the validity of the models and their fidelity to clinical syndromes. We propose that the clinical diseases associated with pulmonary fibrosis, although manifesting a broad array of widely different clinical presentations and features, result in essentially two distinct phenotypes of fibrosis that we will describe. The most common and problematic of these are not effectively modeled experimentally. In this review, we present several clinical entities as examples of the phenotypic distinctions. The first two represent the extremes: postinflammatory fibrosis observed in hypersensitivity pneumonitis (HP) and dysregulated matrix deposition as observed in idiopathic pulmonary fibrosis (IPF). We also present a third clinical entity, that of lung disease associated with rheumatoid arthritis (rheumatoid lung), representing a condition that can manifest as either phenotype, and offering a potential opportunity to explore the mechanisms underlying the pathogenesis of the two distinct fibrotic phenotypes.