T regulatory cells and attenuated bleomycin-induced fibrosis in lungs of CCR7-/- mice

Local, Quantitative Morphometry of Fibroproliferative Lung Injury Using Laminin

Investigations into the mechanisms of injury and repair in fibroproliferative disease require consideration of the spatial heterogeneity inherent in the disease. Most scoring of fibrotic remodeling in preclinical animal models relies on the modified Ashcroft score, which is an ordinal rubric of macroscopic resolution. The obvious limitations of manual histopathologic scoring have generated an unmet need for unbiased, repeatable scoring of fibroproliferative burden in tissue. Using computer vision approaches on immunofluorescence imaging of the extracellular matrix component laminin, we generated a robust and repeatable quantitative remodeling scorer. In the bleomycin lung injury model, the quantitative remodeling scorer shows significant agreement with the modified Ashcroft scale. This antibody-based approach is easily integrated into larger multiplex immunofluorescence experiments, which we demonstrate by testing the spatial apposition of tertiary lymphoid structures to fibroproliferative tissue, a poorly characterized phenomenon observed in both human interstitial lung diseases and preclinical models of lung fibrosis. The tool reported in this article is available as a stand-alone application that is usable without programming knowledge.

Comparative Study of Ectopic Lymphoid Aggregates in Sheep and Murine Models of Bleomycin-Induced Pulmonary Fibrosis

Idiopathic pulmonary fibrosis (IPF) is a chronic disease characterized by excessive deposition of extracellular matrix in the interstitial lung parenchyma, often manifested by dyspnea and progressive loss of lung function. The role of inflammation in the pathogenesis of IPF is not well understood. This study evaluated the histopathological and inflammatory components of bleomycin-induced pulmonary fibrosis in mouse and sheep models, in terms of their ability to translate to the human IPF. Merino sheep (n = 8) were bronchoscopically administered with two bleomycin infusions, two weeks apart, into a caudal lung segment, with a saline (control) administered into a caudal segment in the opposite lung. Balb/c mice were twice intranasally instilled, one week apart, with either bleomycin (n = 7); or saline (control, n = 7). Lung samples were taken for the histopathological assessment 28 days in sheep and 21 days in mice after the first bleomycin administration. We observed tertiary lymphoid aggregates, in the fibrotic lung parenchyma of sheep, but not in mouse lung tissues exposed to bleomycin. B-cell and T-cell infiltration significantly increased in sheep lung tissues compared to mouse lung tissues due to bleomycin injury. Statistical analysis showed that the fibrotic score, fibrotic fraction, and tissue fraction significantly increased in sheep lung tissues compared to murine lung tissues. The presence of tertiary lymphoid aggregates in the lung parenchyma and increased infiltration of T-cells and B-cells, in the sheep model, may be useful for the future study of the underlying inflammatory disease mechanisms in the lung parenchyma of IPF patients.

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.

CCL21 and IP10 as serum biomarkers for pulmonary involvement in systemic lupus erythematosus

BACKGROUND

Although the significance of inflammatory cytokines and chemokines in the pathogenesis of SLE is well established, the findings showed diversity and implied that combining different biomarkers could be useful in monitoring disease activity or organ involvement. Despite the potentially high prevalence of lung involvement in SLE, only a few studies have investigated for lung biomarkers.

OBJECTIVE

The aim of this study was to assess the value of Chemokine Ligand 21 (CCL 21) and Interferon gamma-induced protein 10 (IP10) as serum biomarkers for pulmonary involvement in SLE and their correlation with disease activity, organ involvement, pulmonary function tests (PFTs), and chest CT findings.

MATERIALS AND METHODS

Sixty SLE patients and 30 age- and sex-matched controls were enrolled into this study. All patients underwent serological tests, PFTs, and chest CT examination. The serum levels of CCL21 and IP10 were analyzed, and their correlations with PFTs and CT were explored.

RESULTS

SLE patients with pulmonary involvement had higher serum CCL21 and IP10 levels compared to those without pulmonary involvement which in turn had higher levels than the controls. There were strong negative correlations between CCL21 and IP10 and FEV1, FVC, and DLCO. There were also strong correlations between both biomarkers and HRCT and pulmonary damage, but no correlation with other disease manifestations. Serum level of 2095 pg/mL for CCL21 and 7185 pg/mL for IP10 could detect pulmonary involvement in SLE with a sensitivity of 83.7% and a specificity of 94.1%. Both biomarkers performed equally well in detecting SLE pulmonary involvement with a strong agreement between them (κ = 0.86, p < .001), but CCL21 was better correlated with PFT abnormalities.

CONCLUSION

Both CCL21 and IP10 are serum biomarkers to detect pulmonary involvement in SLE with high sensitivity and specificity. CCL21 correlates better with PFT abnormalities.

Modulation of the Immune System Promotes Tissue Regeneration

The immune system plays an essential role in the angiogenesis, repair, and regeneration of damaged tissues. Therefore, the design of scaffolds that manipulate immune cells and factors in such a way that could accelerate the repair of damaged tissues, following implantation, is one of the main goals of regenerative medicine. However, before manipulating the immune system, the function of the various components of the immune system during the repair process should be well understood and the fabrication conditions of the manipulated scaffolds should be brought closer to the physiological state of the body. In this article, we first review the studies aimed at the role of distinct immune cell populations in angiogenesis and support of damaged tissue repair. In the second part, we discuss the use of strategies that promote tissue regeneration by modulating the immune system. Given that various studies have shown an increase in tissue repair rate with the addition of stem cells and growth factors to the scaffolds, and regarding the limited resources of stem cells, we suggest the design of scaffolds that are capable to develop repair of damaged tissue by manipulating the immune system and create an alternative for repair strategies that use stem cells or growth factors.

Deletion of Myeloid Interferon Regulatory Factor 4 (Irf4) in Mouse Model Protects against Kidney Fibrosis after Ischemic Injury by Decreased Macrophage Recruitment and Activation

BACKGROUND

AKI is characterized by abrupt and reversible kidney dysfunction, and incomplete recovery leads to chronic kidney injury. Previous studies by us and others have indicated that macrophage infiltration and polarization play key roles in recovery from AKI. The role in AKI recovery played by IFN regulatory factor 4 (IRF4), a mediator of polarization of macrophages to the M2 phenotype, is unclear.

METHODS

We used mice with myeloid or macrophage cell-specific deletion of Irf4 (MΦ Irf4^-/- ) to evaluate Irf4's role in renal macrophage polarization and development of fibrosis after severe AKI.

RESULTS

Surprisingly, although macrophage Irf4 deletion had a minimal effect on early renal functional recovery from AKI, it resulted in decreased renal fibrosis 4 weeks after severe AKI, in association with less-activated macrophages. Macrophage Irf4 deletion also protected against renal fibrosis in unilateral ureteral obstruction. Bone marrow-derived monocytes (BMDMs) from MΦ Irf4^-/- mice had diminished chemotactic responses to macrophage chemoattractants, with decreased activation of AKT and PI3 kinase and increased PTEN expression. PI3K and AKT inhibitors markedly decreased chemotaxis in wild-type BMDMs, and in a cultured macrophage cell line. There was significant inhibition of homing of labeled Irf4^-/- BMDMs to postischemic kidneys. Renal macrophage infiltration in response to AKI was markedly decreased in MΦ Irf4^-/- mice or in wild-type mice with inhibition of AKT activity.

CONCLUSIONS

Deletion of Irf4 from myeloid cells protected against development of tubulointerstitial fibrosis after severe ischemic renal injury in mice, due primarily to inhibition of AKT-mediated monocyte recruitment to the injured kidney and reduced activation and subsequent polarization into a profibrotic M2 phenotype.

Regulatory Immune Cells in Idiopathic Pulmonary Fibrosis: Friends or Foes?

The immune system is receiving increasing attention for interstitial lung diseases, as knowledge on its role in fibrosis development and response to therapies is expanding. Uncontrolled immune responses and unbalanced injury-inflammation-repair processes drive the initiation and progression of idiopathic pulmonary fibrosis. The regulatory immune system plays important roles in controlling pathogenic immune responses, regulating inflammation and modulating the transition of inflammation to fibrosis. This review aims to summarize and critically discuss the current knowledge on the potential role of regulatory immune cells, including mesenchymal stromal/stem cells, regulatory T cells, regulatory B cells, macrophages, dendritic cells and myeloid-derived suppressor cells in idiopathic pulmonary fibrosis. Furthermore, we review the emerging role of regulatory immune cells in anti-fibrotic therapy and lung transplantation. A comprehensive understanding of immune regulation could pave the way towards new therapeutic or preventive approaches in idiopathic pulmonary fibrosis.

Pulmonary toxicants and fibrosis: innate and adaptive immune mechanisms

Pulmonary fibrosis is characterized by destruction and remodeling of the lung due to an accumulation of collagen and other extracellular matrix components in the tissue. This results in progressive irreversible decreases in lung capacity, impaired gas exchange and eventually, hypoxemia. A number of inhaled and systemic toxicants including bleomycin, silica, asbestos, nanoparticles, mustard vesicants, nitrofurantoin, amiodarone, and ionizing radiation have been identified. In this article, we review the role of innate and adaptive immune cells and mediators they release in the pathogenesis of fibrotic pathologies induced by pulmonary toxicants. A better understanding of the pathogenic mechanisms underlying fibrogenesis may lead to the development of new therapeutic approaches for patients with these debilitating and largely irreversible chronic diseases.

Lymphatic Proliferation Ameliorates Pulmonary Fibrosis after Lung Injury

Despite many reports about pulmonary blood vessels in lung fibrosis, the contribution of lymphatics to fibrosis is unknown. We examined the mechanism and consequences of lymphatic remodeling in mice with lung fibrosis after bleomycin injury or telomere dysfunction. Widespread lymphangiogenesis was observed after bleomycin treatment and in fibrotic lungs of prospero homeobox 1-enhanced green fluorescent protein (Prox1-EGFP) transgenic mice with telomere dysfunction. In loss-of-function studies, blocking antibodies revealed that lymphangiogenesis 14 days after bleomycin treatment was dependent on vascular endothelial growth factor (Vegf) receptor 3 signaling, but not on Vegf receptor 2. Vegfc gene and protein expression increased specifically. Extensive extravasated plasma, platelets, and macrophages at sites of lymphatic growth were potential sources of Vegfc. Lymphangiogenesis peaked at 14 to 28 days after bleomycin challenge, was accompanied by doubling of chemokine (C-C motif) ligand 21 in lung lymphatics and tertiary lymphoid organ formation, and then decreased as lung injury resolved by 56 days. In gain-of-function studies, expansion of the lung lymphatic network by transgenic overexpression of Vegfc in club cell secretory protein (CCSP)/VEGF-C mice reduced macrophage accumulation and fibrosis and accelerated recovery after bleomycin treatment. These findings suggest that lymphatics have an overall protective effect in lung injury and fibrosis and fit with a mechanism whereby lung lymphatic network expansion reduces lymph stasis and increases clearance of fluid and cells, including profibrotic macrophages.

Amniotic MSCs reduce pulmonary fibrosis by hampering lung B-cell recruitment, retention, and maturation

Growing evidence suggests a mechanistic link between inflammation and the development and progression of fibrotic processes. Mesenchymal stromal cells derived from the human amniotic membrane (hAMSCs), which display marked immunomodulatory properties, have been shown to reduce bleomycin‐induced lung fibrosis in mice, possibly by creating a microenvironment able to limit the evolution of chronic inflammation to fibrosis. However, the ability of hAMSCs to modulate immune cells involved in bleomycin‐induced pulmonary inflammation has yet to be elucidated. Herein, we conducted a longitudinal study of the effects of hAMSCs on alveolar and lung immune cell populations upon bleomycin challenge. Immune cells collected through bronchoalveolar lavage were examined by flow cytometry, and lung tissues were used to study gene expression of markers associated with different immune cell types. We observed that hAMSCs increased lung expression of T regulatory cell marker Foxp3, increased macrophage polarization toward an anti‐inflammatory phenotype (M2), and reduced the antigen‐presentation potential of macrophages and dendritic cells. For the first time, we demonstrate that hAMSCs markedly reduce pulmonary B‐cell recruitment, retention, and maturation, and counteract the formation and expansion of intrapulmonary lymphoid aggregates. Thus, hAMSCs may hamper the self‐maintaining inflammatory condition promoted by B cells that continuously act as antigen presenting cells for proximal T lymphocytes in injured lungs. By modulating B‐cell response, hAMSCs may contribute to blunting of the chronicization of lung inflammatory processes with a consequent reduction of the progression of the fibrotic lesion.

Regulatory T cells are a double-edged sword in pulmonary fibrosis

Pulmonary fibrosis (PF) is a chronic progressive interstitial lung disease. The pathogenesis of PF has not been clearly elucidated, and there is no obvious effective treatment to arrest the progression of PF to date. A long-term chronic inflammatory response and inappropriate repair process after lung injury are important causes and pathological processes of PF. As an influential type of the body's immune cells, regulatory T cells (Tregs) play an irreplaceable role in inhibiting the inflammatory response and promoting the repair of lung tissue. However, the exact roles of Tregs in the process of PF have not been clearly established, and the available literature concerning the roles of Tregs in PF are contradictory. First, Tregs can advance the progression of pulmonary fibrosis by secreting platelet-derived growth factor (PDGF), transforming growth factor-β (TGF-β) and other related factors, promoting epithelial-mesenchymal transition (EMT) and affecting the Th1 and Th2 balance, etc. Second, Tregs can inhibit PF by promoting the repair of epithelial cell damage, inhibiting the accumulation of fibroblasts, and strongly inhibiting the production and function of other related pro-inflammatory factors and pro-inflammatory cells. Accordingly, in this review, we focus on the multiple roles of Tregs in different models and different pulmonary fibrosis phases, thereby providing theoretical support for a better understanding of the multiple roles of these cells in PF and a theoretical basis for identifying targets for PF therapy.

Regulatory T Cells Limit Pneumococcus-Induced Exacerbation of Lung Fibrosis in Mice

Patients with idiopathic pulmonary fibrosis (IPF) can experience life-threatening episodes of acute worsening of their disease, termed acute exacerbation of IPF, which may be caused by bacterial and/or viral infections. The potential for regulatory T cells (Tregs) to limit disease progression in bacterially triggered fibrosis exacerbation has not been explored so far. In the current study, we show that the number of Tregs was significantly increased in mice with established AdTGF-β1-induced lung fibrosis and further increased in mice with pneumococcal infection-induced lung fibrosis exacerbation. Diphtheria toxin-induced depletion of Tregs significantly worsened infection-induced fibrosis exacerbation as determined by increased lung collagen deposition, lung histology, and elevated pulmonary Th1/Th2 cytokine levels. Conversely, IL-2 complex-induced Treg expansion in wild-type mice with established lung fibrosis completely inhibited pneumococcal infection-induced fibrosis exacerbation as efficaciously as antibiotic treatment while preserving lung antibacterial immunity in mice. Collectively, these findings demonstrate the efficacy of Tregs as "silencers," suppressing infection-induced exacerbation of lung fibrosis in mice, and their expansion may offer a novel adjunctive treatment to limit acute exacerbations in patients with IPF.

Using evasins to target the chemokine network in inflammation

Inflammation, is driven by a network comprising cytokines, chemokines, their target receptors and leukocytes, and is a major pathologic mechanism that adversely affects organ function in diverse human diseases. Despite being supported by substantial target validation, no successful anti-chemokine therapeutic to treat inflammatory disease has yet been developed. This is in part because of the robustness of the chemokine network, which emerges from a large total chemokine load in disease, promiscuous expression of receptors on leukocytes, promiscuous and synergistic interactions between chemokines and receptors, and feedforward loops created by secretion of chemokines by leukocytes themselves. Many parasites, including viruses, helminths and ticks, evade the chemokine network by producing proteins that bind promiscuously to chemokines or their receptors. Evasins - three small glycoproteins identified in the saliva of the brown dog tick - bind multiple chemokines, and are active in several animal models of inflammatory disease. Over 50 evasin homologs have recently been identified from diverse tick species. Characterization of the chemokine binding patterns of evasins show that several have anti-chemokine activities that extend substantially beyond those previously described. These studies indicate that evasins function at the site of the tick bite by reducing total chemokine load. This not only reduces chemokine signaling to receptors, but also interrupts feedforward loops, thus disabling the chemokine network. Taking the lead from nature, a goal for the development of new anti-chemokine therapeutics would be to reduce the total chemokine load in disease. This could be achieved by administering appropriate evasin combinations or by smaller peptides that mimic evasin action.

Role of iBALT in Respiratory Immunity

Pulmonary respiration inevitably exposes the mucosal surface of the lung to potentially noxious stimuli, including pathogens, allergens, and particulates, each of which can trigger pulmonary damage and inflammation. As inflammation resolves, B and T lymphocytes often aggregate around large bronchi to form inducible Bronchus-Associated Lymphoid Tissue (iBALT). iBALT formation can be initiated by a diverse array of molecular pathways that converge on the activation and differentiation of chemokine-expressing stromal cells that serve as the scaffolding for iBALT and facilitate the recruitment, retention, and organization of leukocytes. Like conventional lymphoid organs, iBALT recruits naïve lymphocytes from the blood, exposes them to local antigens, in this case from the airways, and supports their activation and differentiation into effector cells. The activity of iBALT is demonstrably beneficial for the clearance of respiratory pathogens; however, it is less clear whether it dampens or exacerbates inflammatory responses to non-infectious agents. Here, we review the evidence regarding the role of iBALT in pulmonary immunity and propose that the final outcome depends on the context of the disease.

Impact of Treg on other T cell subsets in progression of fibrosis in experimental lung fibrosis

Idiopathic pulmonary fibrosis is an irreversible, progressive and lethal lung disease. Regulatory T cells (Tregs) and Th17 cells both are involved in lung fibrosis. But there are only few reports regarding the effect of Treg on other T cell subsets in experimental lung fibrosis. The aim of this study was to investigate the impact of Treg on Th17, CD4+CD28-T, CD4+CD28+T and CD8 + T cell subsets that could drive lung fibrosis. To reach the goal of our study, first we depleted Tregs by anti-CD25 mAb injection in experimental C57BL/6 mice model. It has been demonstrated in our study that depletion of Treg ameliorates bleomycin-induced lung fibrosis by immune modulating Th17 and other important T cell subsets response in lung. Our flow cytometry data revealed that the percentages of Th17, CD4+CD28-T, CD4+CD28+T and CD8 + T cell subsets were decreased in experimental lung fibrosis after Treg depletion. We also observed significant downregulation of IL-17 A in Treg-depleted mice after bleomycin delivery. In addition, the study also suggested that Treg depletion led to considerable upregulation of IFN-γ after bleomycin administration. Therefore, Th17 cells, CD8 + T cells, CD4+CD28- and CD4+CD28+ T cell subsets all are controlled by regulatory T cell, help in progression of fibrosis in experimental lung fibrosis.

The diversity of myeloid immune cells shaping wound repair and fibrosis in the lung

In healthy circumstances the immune system coordinates tissue repair responses in a tight balance that entails efficient inflammation for removal of potential threats, proper wound closure, and regeneration to regain tissue function. Pathological conditions, continuous exposure to noxious agents, and even ageing can dysregulate immune responses after injury. This dysregulation can lead to a chronic repair mechanism known as fibrosis. Alterations in wound healing can occur in many organs, but our focus lies with the lung as it requires highly regulated immune and repair responses with its continuous exposure to airborne threats. Dysregulated repair responses can lead to pulmonary fibrosis but the exact reason for its development is often not known. Here, we review the diversity of innate immune cells of myeloid origin that are involved in tissue repair and we illustrate how these cell types can contribute to the development of pulmonary fibrosis. Moreover, we briefly discuss the effect of age on innate immune responses and therefore on wound healing and we conclude with the implications of current knowledge on the avenues for future research.

Dendritic Cell Trafficking and Function in Rare Lung Diseases

Dendritic cells (DCs) are highly specialized immune cells that capture antigens and then migrate to lymphoid tissue and present antigen to T cells. This critical function of DCs is well defined, and recent studies further demonstrate that DCs are also key regulators of several innate immune responses. Studies focused on the roles of DCs in the pathogenesis of common lung diseases, such as asthma, infection, and cancer, have traditionally driven our mechanistic understanding of pulmonary DC biology. The emerging development of novel DC reagents, techniques, and genetically modified animal models has provided abundant data revealing distinct populations of DCs in the lung, and allow us to examine mechanisms of DC development, migration, and function in pulmonary disease with unprecedented detail. This enhanced understanding of DCs permits the examination of the potential role of DCs in diseases with known or suspected immunological underpinnings. Recent advances in the study of rare lung diseases, including pulmonary Langerhans cell histiocytosis, sarcoidosis, hypersensitivity pneumonitis, and pulmonary fibrosis, reveal expanding potential pathogenic roles for DCs. Here, we provide a review of DC development, trafficking, and effector functions in the lung, and discuss how alterations in these DC pathways contribute to the pathogenesis of rare lung diseases.

Increased activated regulatory T cells proportion correlate with the severity of idiopathic pulmonary fibrosis

Background

Regulatory T cells (Tregs) are crucial in maintaining immune tolerance and immune homeostasis, but their role in idiopathic pulmonary fibrosis (IPF) is unclear. This study was designed to explore the role of Tregs in IPF.

Methods

Percentages of Tregs and their subpopulations in peripheral blood (PB) and bronchoalveolar lavage (BAL) samples were determined by flow cytometry in 29 patients with IPF, 19 patients with primary Sjögren’s syndrome-related interstitial pneumonia (pSS-IP), and 23 healthy controls (HCs).

Results

In peripheral blood, no difference was found in CD4⁺CD25⁺Foxp3⁺ Treg percentages among patients with IPF, pSS-IP, or HCs. However, activated Treg (aTreg) fractions among CD4⁺ T cells increased significantly in IPF compared with pSS-IP or HCs. Being consistent with the result from the PB, aTreg fractions among CD4⁺ T cells in IPF also increased significantly compared with pSS-IP or HCs, accompanied by increased fraction III compared with HCs in BAL. IPF patients had lower levels of resting Tregs (rTregs) from the thymus than did HCs, whereas aTreg levels originating from the thymus did not significantly differ from HCs. Both rTregs and aTregs proliferated in IPF, with aTregs being more proliferative than rTregs. Both rTregs and aTregs significantly inhibited proliferation of CD4⁺ T lymphocytes in vitro. The percentage of aTregs was correlated negatively with predicted diffusing capacity values for carbon monoxide and positively with GAP index in IPF.

Conclusions

Our study showed the imbalance between subpopulations of Tregs in IPF. Increased aTregs proportion in the peripheral blood correlated inversely with disease severity.

Pulmonary CCR2+CD4+ T cells are immune regulatory and attenuate lung fibrosis development

BACKGROUND

Animal models have suggested that CCR2-dependent signalling contributes to the pathogenesis of pulmonary fibrosis, but global blockade of CCL2 failed to improve the clinical course of patients with lung fibrosis. However, as levels of CCR2⁺CD4⁺ T cells in paediatric lung fibrosis had previously been found to be increased, correlating with clinical symptoms, we hypothesised that distinct CCR2⁺ cell populations might either increase or decrease disease pathogenesis depending on their subtype.

OBJECTIVE

To investigate the role of CCR2⁺CD4⁺ T cells in experimental lung fibrosis and in patients with idiopathic pulmonary fibrosis and other fibrosis.

METHODS

Pulmonary CCR2⁺CD4⁺ T cells were analysed using flow cytometry and mRNA profiling, followed by in silico pathway analysis, in vitro assays and adoptive transfer experiments.

RESULTS

Frequencies of CCR2⁺CD4⁺ T cells were increased in experimental fibrosis-specifically the CD62L^-CD44⁺ effector memory T cell phenotype, displaying a distinct chemokine receptor profile. mRNA profiling of isolated CCR2⁺CD4⁺ T cells from fibrotic lungs suggested immune regulatory functions, a finding that was confirmed in vitro using suppressor assays. Importantly, adoptive transfer of CCR2⁺CD4⁺ T cells attenuated fibrosis development. The results were partly corroborated in patients with lung fibrosis, by showing higher percentages of Foxp3⁺ CD25⁺ cells within bronchoalveolar lavage fluid CCR2⁺CD4⁺ T cells as compared with CCR2^-CD4⁺ T cells.

CONCLUSION

Pulmonary CCR2⁺CD4⁺ T cells are immunosuppressive, and could attenuate lung inflammation and fibrosis. Therapeutic strategies completely abrogating CCR2-dependent signalling will therefore also eliminate cell populations with protective roles in fibrotic lung disease. This emphasises the need for a detailed understanding of the functions of immune cell subsets in fibrotic lung disease.

Heterogeneity of Fibroblasts and Myofibroblasts in Pulmonary Fibrosis

PURPOSE OF REVIEW

Idiopathic Pulmonary Fibrosis (IPF) is the most common form of interstitial lung diseases of unknown eathiopathogenesis, mean survival of 3-5 years and limited therapeutics. Characterized by a loss of alveolar type II epithelial cells and aberrant activation of stromal cells, considerable effort was undertaken to characterize the origin and activation mechanisms of fibroblasts and myofibroblasts in IPF lungs. In this review, the origin and contribution of fibroblast and myofibroblasts in lung fibrosis will be summarized.

RECENT FINDINGS

Lineage tracing experiments suggested that interstitial lung fibroblasts and lipofibroblasts, pericytes and mesothelial cells differentiate into myofibroblasts. However, epithelial and bone marrow derived cells may give rise to collagen expressing fibroblasts but do not differentiate into myofibroblasts.

SUMMARY

There is great heterogeneity in fibroblasts and myofibroblasts in fibrotic lungs. Further, there is evidence for the expansion of pericyte derived myofibroblasts and loss of lipofibroblasts and lipofibroblast derived myofibroblasts in IPF.

Cancer-FOXP3 directly activated CCL5 to recruit FOXP3+Treg cells in pancreatic ductal adenocarcinoma

Forkheadbox protein 3 (FOXP3), initially identified as a key transcription factor for regulatory T cells (Treg cells), was also expressed in many tumors including pancreatic ductal adenocarcinoma (PDAC). However, its role in PDAC progression remains elusive. In this study, we utilized 120 PDAC tissues after radical resection to detect cancer-FOXP3 and Treg cells by immunohistochemistry and evaluated clinical and pathological features of these patients. Cancer-FOXP3 was positively correlated with Treg cells accumulation in tumor tissues derived from PDAC patients. In addition, high cancer-FOXP3 expression was associated with increased tumor volumes and poor prognosis in PDAC especially combined with high levels of Treg cells. Overexpression of cancer-FOXP3 promoted the tumor growth in immunocompetent syngeneic mice but not in immunocompromised or Treg cell-depleted mice. Furthermore, CCL5 was directly trans-activated by cancer-FOXP3 and promoted the recruitment of Treg cells from peripheral blood to the tumor site in vitro and in vivo. This finding has been further reinforced by the evidence that Treg cells recruitment by cancer-FOXP3 was impaired by neutralization of CCL5, thereby inhibiting the growth of PDAC. In conclusion, cancer-FOXP3 serves as a prognostic biomarker and a crucial determinant of immunosuppressive microenvironment via recruiting Treg cells by directly trans-activating CCL5. Therefore, cancer-FOXP3 could be used to select patients with better response to CCL5/CCR5 blockade immunotherapy.

Promoting tissue regeneration by modulating the immune system

The immune system plays a central role in tissue repair and regeneration. Indeed, the immune response to tissue injury is crucial in determining the speed and the outcome of the healing process, including the extent of scarring and the restoration of organ function. Therefore, controlling immune components via biomaterials and drug delivery systems is becoming an attractive approach in regenerative medicine, since therapies based on stem cells and growth factors have not yet proven to be broadly effective in the clinic. To integrate the immune system into regenerative strategies, one of the first challenges is to understand the precise functions of the different immune components during the tissue healing process. While remarkable progress has been made, the immune mechanisms involved are still elusive, and there is indication for both negative and positive roles depending on the tissue type or organ and life stage. It is well recognized that the innate immune response comprising danger signals, neutrophils and macrophages modulates tissue healing. In addition, it is becoming evident that the adaptive immune response, in particular T cell subset activities, plays a critical role. In this review, we first present an overview of the basic immune mechanisms involved in tissue repair and regeneration. Then, we highlight various approaches based on biomaterials and drug delivery systems that aim at modulating these mechanisms to limit fibrosis and promote regeneration. We propose that the next generation of regenerative therapies may evolve from typical biomaterial-, stem cell-, or growth factor-centric approaches to an immune-centric approach.

STATEMENT OF SIGNIFICANCE

Most regenerative strategies have not yet proven to be safe or reasonably efficient in the clinic. In addition to stem cells and growth factors, the immune system plays a crucial role in the tissue healing process. Here, we propose that controlling the immune-mediated mechanisms of tissue repair and regeneration may support existing regenerative strategies or could be an alternative to using stem cells and growth factors. The first part of this review we highlight key immune mechanisms involved in the tissue healing process and marks them as potential target for designing regenerative strategies. In the second part, we discuss various approaches using biomaterials and drug delivery systems that aim at modulating the components of the immune system to promote tissue regeneration.

Levels of hepatic Th17 cells and regulatory T cells upregulated by hepatic stellate cells in advanced HBV-related liver fibrosis

Background

Liver fibrosis which mainly occurs upon chronic hepatitis virus infection potentially leads to portal hypertension, hepatic failure and hepatocellular carcinoma. However, the immune status of Th17 and Treg cells in liver fibrosis is controversial and the exact mechanisms remain largely elusive.

Methods

Liver tissues and peripheral blood were obtained simultaneously from 32 hepatitis B virus infected patients undergoing surgery for hepatocellular carcinoma at the medical center of Sun Yat-sen University. Liver tissues at least 3 cm away from the tumor site were used for the analyses. Levels of Th17 cells and regulatory T cells were detected by flow cytometry analysis and immunohistochemistry. In vitro experiment, we adopted magnetic cell sorting to investigate how hepatic stellate cells regulate the levels of Th17 cells and regulatory T cells.

Results

We found that hepatic Th17 cells and regulatory T cells were increased in patients with advanced stage HBV-related liver fibrosis. Hepatic stellate cells upregulated the levels of Th17 cells and regulatory T cells via PGE2/EP2 and EP4 pathway.

Conclusions

We found that the increased levels of Th17 cells and regulatory T cells were upregulated by hepatic stellate cells. These results may provide insight into the role of hepatic stellate cells and Th17 cells and regulatory T cells in the persistence of fibrosis and into the occurrence of hepatocellular carcinoma following cirrhosis.

Electronic supplementary material

The online version of this article (doi:10.1186/s12967-017-1167-y) contains supplementary material, which is available to authorized users.

The Role of Lymphocytes in Radiotherapy-Induced Adverse Late Effects in the Lung

Radiation-induced pneumonitis and fibrosis are dose-limiting side effects of thoracic irradiation. Thoracic irradiation triggers acute and chronic environmental lung changes that are shaped by the damage response of resident cells, by the resulting reaction of the immune system, and by repair processes. Although considerable progress has been made during the last decade in defining involved effector cells and soluble mediators, the network of pathophysiological events and the cellular cross talk linking acute tissue damage to chronic inflammation and fibrosis still require further definition. Infiltration of cells from the innate and adaptive immune systems is a common response of normal tissues to ionizing radiation. Herein, lymphocytes represent a versatile and wide-ranged group of cells of the immune system that can react under specific conditions in various ways and participate in modulating the lung environment by adopting pro-inflammatory, anti-inflammatory, or even pro- or anti-fibrotic phenotypes. The present review provides an overview on published data about the role of lymphocytes in radiation-induced lung disease and related damage-associated pulmonary diseases with a focus on T lymphocytes and B lymphocytes. We also discuss the suspected dual role of specific lymphocyte subsets during the pneumonitic phase and fibrotic phase that is shaped by the environmental conditions as well as the interaction and the intercellular cross talk between cells from the innate and adaptive immune systems and (damaged) resident epithelial cells and stromal cells (e.g., endothelial cells, mesenchymal stem cells, and fibroblasts). Finally, we highlight potential therapeutic targets suited to counteract pathological lymphocyte responses to prevent or treat radiation-induced lung disease.

CCL21 and IP-10 as blood biomarkers for pulmonary involvement in systemic lupus erythematosus patients

Biomarkers for pulmonary manifestations in systemic lupus erythematosus (SLE) are missing. Plasma samples of nine SLE patients with known pulmonary involvement (SLEpulm) and nine SLE patients without pulmonary involvement (SLE) were tested by multiplex microarray analysis for various cyto- and chemokines. Significantly decreased lung function paramters for forced vital capacity (FVC), total lung capacity (TLC), diffusion capacity for carbon monoxide (DLCO) and diffusion of CO corrected on lung volume (KLCO) were observed in SLEpulm as compared to SLE patients. CC chemokine ligand 21 (CCL21) and interferon gamma-induced protein 10 (IP-10) levels were significantly higher in SLEpulm, than in patients without pulmonary manifestations. CCL21 correlated negatively with DLCO ( r = −0.73; p < 0.01) and KLCO ( r = −0.62; p < 0.01), while IP-10 with FVC and forced expiratory volume one second. Receiver Operating Characteristics (ROC) analysis confirmed high sensitivity and specificity for the separation of SLE patients with and without pulmonary involvement for the chemokines CCL21 (Area Under Curve (AUC): 0.85; sensitivity%: 88.90; specificity%: 75.00; p < 0.01) and IP-10 (AUC: 0.82; sensitivity%: 66.67, specificity%: 100; p < 0.01). Pleuropulmonary manifestations in SLE patients associated with lung functional and DLCO/KLCO changes and were associated with significant increase in CCL21 and IP-10. These chemokines might serve as potential biomarkers of lung involvement in SLE patients.

Inducible Bronchus-Associated Lymphoid Tissue: Taming Inflammation in the Lung

Following pulmonary inflammation, leukocytes that infiltrate the lung often assemble into structures known as inducible Bronchus-Associated Lymphoid Tissue (iBALT). Like conventional lymphoid organs, areas of iBALT have segregated B and T cell areas, specialized stromal cells, high endothelial venules, and lymphatic vessels. After inflammation is resolved, iBALT is maintained for months, independently of inflammation. Once iBALT is formed, it participates in immune responses to pulmonary antigens, including those that are unrelated to the iBALT-initiating antigen, and often alters the clinical course of disease. However, the mechanisms that govern immune responses in iBALT and determine how iBALT impacts local and systemic immunity are poorly understood. Here, we review our current understanding of iBALT formation and discuss how iBALT participates in pulmonary immunity.

Gq-Coupled Receptors in Autoimmunity

Heterotrimeric G proteins can be divided into Gi, Gs, Gq/11, and G12/13 subfamilies according to their α subunits. The main function of G proteins is transducing signals from G protein coupled receptors (GPCRs), a family of seven transmembrane receptors. In recent years, studies have demonstrated that GPCRs interact with Gq, a member of the Gq/11 subfamily of G proteins. This interaction facilitates the vital role of this family of proteins in immune regulation and autoimmunity, particularly for Gαq, which is considered the functional α subunit of Gq protein. Therefore, understanding the mechanisms through which Gq-coupled receptors control autoreactive lymphocytes is critical and may provide insights into the treatment of autoimmune disorders. In this review, we summarize recent advances in studies of the role of Gq-coupled receptors in autoimmunity, with a focus on their pathologic role and downstream signaling.

Treg Cell Differentiation: From Thymus to Peripheral Tissue

Regulatory T cells (Tregs) are crucial mediators of self-tolerance in the periphery. They differentiate in the thymus, where interactions with thymus-resident antigen-presenting cells, an instructive cytokine milieu, and stimulation of the T cell receptor lead to the selection into the Treg lineage and the induction of Foxp3 gene expression. Once mature, Treg cells leave the thymus and migrate into either the secondary lymphoid tissues, e.g., lymph nodes and spleen, or peripheral nonlymphoid tissues. There is growing evidence that Treg cells go beyond the classical modulation of immune responses and also play important functional roles in nonlymphoid peripheral tissues. In this review, we summarize recent findings about the thymic Treg lineage differentiation as well as the further specialization of Treg cells in the secondary lymphoid and in the peripheral nonlymphoid organs.

Treg depletion attenuates irradiation-induced pulmonary fibrosis by reducing fibrocyte accumulation, inducing Th17 response, and shifting IFN-γ, IL-12/IL-4, IL-5 balance

Irradiation-induced pulmonary fibrosis results from thoracic radiotherapy and severely limits radiotherapy approaches. CD4(+) CD25(+) FoxP3(+) regulatory T cells (Tregs) are involved in experimentally induced murine lung fibrosis. However, the precise contribution of Tregs to irradiation-induced pulmonary fibrosis still remains unclear. We have previously established the mouse model of irradiation-induced pulmonary fibrosis and observed an increased frequency of Tregs during the process. This study aimed to investigate the effects of Treg depletion on irradiation-induced pulmonary fibrosis and on fibrocyte, Th17 cell response and production of multiple cytokines in mice. Treg-depleted mice were generated by intraperitoneal injection with anti-CD25 mAb 2h after 20 Gy (60)CO γ-ray thoracic irradiation and every 7 days thereafter. Pulmonary fibrosis was semi-quantitatively assessed using Masson's trichrome staining. The proportions of Tregs, fibrocyte and Th17 cells were detected by flow cytometry. Th1/Th2 cytokines were assessed by Luminex assays. We found that Treg depletion decelerated the process of irradiation-induced pulmonary fibrosis and hindered fibrocyte recruitment to the lung. In response to Treg depletion, the number of CD4(+) T lymphocytes and Th17 cells increased. Moreover, Th1/Th2 cytokine balance was disturbed into Th1 dominance upon Treg depletion. Our study demonstrates that Tregs are involved in irradiation-induced pulmonary fibrosis by promoting fibrocyte accumulation, attenuating Th17 response and regulating Th1/Th2 cytokine balance in the lung tissues, which suggests that Tregs may be therapeutically manipulated to decelerate the progression of irradiation-induced pulmonary fibrosis.

Different profiles of notch signaling in cigarette smoke-induced pulmonary emphysema and bleomycin-induced pulmonary fibrosis

OBJECTIVE

Different profiles of Notch signaling mediate naive T cell differentiation which might be involved in pulmonary emphysema and fibrosis.

METHODS

C57BL/6 mice were randomized into cigarette smoke (CS) exposure, bleomycin (BLM) exposure, and two separate groups of control for sham exposure to CS or BLM. The paratracheal lymph nodes of the animals were analyzed by real-time PCR and immunohistochemistry. Morphometry of the lung parenchyma, measurement of the cytokines, and cytometry of the bronchoalveolar lavage fluid (BALF) were also done accordingly.

RESULTS

In comparison with controls, all Notch receptors and ligands were upregulated by chronic CS exposure, especially Notch3 and DLL1 (P < 0.01), and this was in line with emphysema-like morphology and Th1-biased inflammation. While Notch3 and DLL1 were downregulated by BLM exposure (P < 0.01), those was in line with fibrotic lung remodeling and Th2 polarization.

CONCLUSIONS

This founding implies that the CS exposure but not the BLM exposure is capable of initiating Notch signaling in lymphoid tissue of the lung, which is likely relevant to the pathogenesis of pulmonary emphysema. Unable to initiate the Th1 response or inhibit it may lead to Th2 polarization and aberrant repair.

CD4+CD25+Foxp3+ regulatory T cells contribute in liver fibrosis improvement with interferon alpha

The aim of this study is to investigate the optimal dose, treatment time, and possible immunologic mechanisms of interferon alpha (IFN-α) in the treatment of liver fibrosis. Mice were injected intraperitoneally with 10 % carbon tetrachloride to induce liver fibrosis, except in the normal control group. The experimental mice were randomly divided into four groups: physiological saline group, 20 U/gb wt IFN-α group, 40 U/gb wt IFN-α group, and 60 U/gb wt IFN-α group. After 3 and 6 weeks, type I collagen was detected in liver by hematoxylin and eosin (HE) stain, Masson's trichrome stain, and immunohistochemical staining. The number of CD8(+) T cells, the number of CD4(+)CD25(+)Foxp3(+) Tregs and the activation of CD4(+) T cells were detected in liver and spleen. Beneficial effects were observed in the 40 U/gb wt IFN-α group by pathological analysis. The number of CD8(+) T cells in the liver was significantly lower in mice receiving middle-dose IFN-α therapy as compared to mice receiving physiological saline (P < 0.05), while CD4(+)CD25(+)Foxp3(+) Tregs and activation of CD4(+) T cells in the liver were significantly higher in the therapeutic group than in the physiological saline group (P < 0.05). CD8(+) T cells (r = 0.3796) and activated CD4(+) T cells (r = 0.2437) were found to be positively correlated with the degree of liver fibrosis. CD4(+)CD25(+)Foxp3(+) Tregs (r = -0.7932) was found to be negatively correlated with the degree of liver fibrosis. IFN-α can inhibit liver fibrosis following 6 weeks of middle-dose IFN-α therapy by upregulating CD4(+)CD25(+)Foxp3(+) Tregs and suppressing CD8(+) T cells.

Transforming growth factor β3 attenuates the development of radiation-induced pulmonary fibrosis in mice by decreasing fibrocyte recruitment and regulating IFN-γ/IL-4 balance

Radiation-induced pulmonary fibrosis is a frequently occurred complication from radiotherapy of thoracic tumors. The transforming growth factor-β (TGF-β) superfamily plays a key regulatory role in pulmonary fibrosis. As TGF-β3 showed the potential anti-fibrotic properties especially in scar-less wound healing as opposed to the fibrotic function of TGF-β1, we sought to explore the role of TGF-β3 in radiation-induced pulmonary fibrosis. A single thoracic irradiation of 20 Gy was applied in mice to establish the model of radiation-induced pulmonary fibrosis and the mice were treated by intraperitoneal injections of recombinant TGF-β3 weekly after irradiation. We found that TGF-β3 decelerated the progress of radiation-induced pulmonary fibrosis and hindered the recruitment of fibrocytes to lung. In addition, Th1 response was suppressed as shown by diminished IFN-γ in bronchoalveolar lavage fluid (BALF) after irradiation, and enhancement of Th2 response was marked by increased IL-4 in BALF. TGF-β3 administration significantly attenuated these effects and increased the percentage of Tregs in lung during the progression of pulmonary fibrosis. Taken together, these data suggest that TGF-β3 might be involved in the regulatory mechanism for attenuation of radiation-induced pulmonary fibrosis.

CD4+CD25+FoxP3+ Regulatory Tregs inhibit fibrocyte recruitment and fibrosis via suppression of FGF-9 production in the TGF-β1 exposed murine lung

Pulmonary fibrosis is a difficult to treat, often fatal disease whose pathogenesis involves dysregulated TGF-β1 signaling. CD4+CD25+FoxP3+ Regulatory T cells (“Tregs”) exert important effects on host tolerance and arise from naïve CD4+ lymphocytes in response to TGF-β1. However, the precise contribution of Tregs to experimentally induced murine lung fibrosis remains unclear. We sought to better understand the role of Tregs in this context. Using a model of fibrosis caused by lung specific, doxycycline inducible overexpression of the bioactive form of the human TGF-β1 gene we find that Tregs accumulate in the lung parenchyma within 5 days of transgene activation and that this enhancement persists to at least 14 days. Anti-CD25 Antibody mediated depletion of Tregs causes increased accumulation of soluble collagen and of intrapulmonary CD45+Col Iα1 fibrocytes. These effects are accompanied by enhanced local concentrations of the classical inflammatory mediators CD40L, TNF-α, and IL-1α, along with the neuroimmune molecule fibroblast growth factor 9 (FGF-9, also known as “glial activating factor”). FGF-9 expression localizes to parenchymal cells and alveolar macrophages in this model and antibody mediated neutralization of FGF-9 results in attenuated detection of intrapulmonary collagen and fibrocytes without affecting Treg quantities. These data indicate that CD4+CD25+FoxP3+ Tregs attenuate TGF-β1 induced lung fibrosis and fibrocyte accumulation in part via suppression of FGF-9.

Synergistic effect of nanosecond pulsed electric field combined with low-dose of pingyangmycin on salivary adenoid cystic carcinoma

Adenoid cystic carcinoma (ACC) is one of the most common malignant neoplasms in salivary glands. To evaluate the therapeutic effects of nanosecond pulsed electric field (nsPEF) combined with pingyangmycin (PYM) on salivary gland adenoid cystic carcinoma (SACC), ACC high metastatic cell line (SACC-LM) and low metastatic cell line (SACC‑83) were tested by CCK-8 assay, cell clonogenic assay, flow cytometry and Transwell assay. Extracellular matrix metalloproteinase inducer (EMMPRIN) expression was tested by western blotting to verify the synergistic mechanism of nsPEF and PYM. The results showed that nsPEF inhibited the cell proliferation of both cell lines, and the inhibitory effect was strongly associated with time and electrical field strength. Moreover, PYM combined with nsPEF may enhance the suppression effect significantly, even at a very low dose (0.01 µg/ml). The synergistic effects may contribute to the downregulation of EMMPRIN expression resulting from the application of nsPEF. For SACC, nsPEF combined with chemotherapy agents may be a valuable strategy not only to improve the treatment effect and prognosis, but also to reduce the side-effects of chemotherapy.

Heterogeneity in fibroblast proliferation and survival in idiopathic pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is the most common form of interstitial lung disease characterized by the persistence of activated myofibroblasts resulting in excessive deposition of extracellular matrix proteins and profound tissue remodeling. Myofibroblasts have been shown to arise from interstitial fibroblasts, epithelial to mesenchymal transition of type II alveolar epithelial cells, and the differentiation of recruited fibrocytes. There are many mechanisms that are utilized by these cells for survival, proliferation, and persistent activation including up-regulation of cytokines [i.e., Interleukin 6 (IL-6) and C-C motif chemokine ligand 21 (CCL21)], cytokine receptors [i.e., Interleukin 6Receptor 1 (IL-6R1), Glycoprotein 130 (gp130) and C-C Chemokine Receptor type 7 (CCR7)], and innate pattern recognition receptors [(PRRs; i.e., Toll Like Receptor 9 (TLR9)]. In this review, we will discuss the role of the cytokines IL-6 and CCL21, their receptors and the PRR, TLR9, in fibroblast recruitment, activation, survival, and differentiation into myofibroblasts in IPF.

Peripheral depletion of NK cells and imbalance of the Treg/Th17 axis in idiopathic pulmonary fibrosis patients

The immune response plays an unsettled role in the pathogenesis of idiopathic pulmonary fibrosis (IPF), the contribution of inflammation being controversial as well. Emerging novel T cell sub-populations including regulatory T lymphocytes (Treg) and interleukin (IL)-17 secreting T helper cells (Th17) may exert antithetical actions in this scenario. Phenotype and frequency of circulating immune cell subsets were assessed by multi-parametric flow cytometry in 29 clinically stable IPF patients and 17 healthy controls. The interplay between Treg lymphocytes expressing transforming growth factor (TGF)-β and Th17 cells was also investigated. Proportion and absolute number of natural killer (NK) cells were significantly reduced in IPF patients in comparison with controls (p<0.001). Conversely, the proportion and absolute number of CD3(+)CD4(+)CD25(high)Foxp-3(+) cells were significantly increased in IPF patients (p=0.000). As in controls, almost the totality of cells (>90%) expressed TGF-β upon stimulation. Interestingly, the frequency of Th17 cells was significantly compromised in IPF patients (p=0.000) leading to an increased TGF-β/IL-17 ratio (4.2±2.3 vs 0.5±0.3 in controls, p=0.000). Depletion of NK and Th17 cells along with a not compromised Treg compartment delineate the existence of an "immune profile" that argue against the recent hypothesis of IPF as an autoimmune disease. Our findings along with the imbalance of the Treg/Th17 axis more closely suggest these immune perturbations to be similar to those observed in cancer. Clinical relevance, limitations and perspectives for future research are discussed.

The absence of CCR7 results in dysregulated monocyte migration and immunosuppression facilitating chronic cutaneous leishmaniasis

The protozoan parasite Leishmania major causes cutaneous lesions to develop at the site of infection, which are resolved with a strong Th1 immune response in resistant hosts, such as C57BL/6 mice. In contrast, the lesions ulcerate in susceptible hosts which display a Th2 response, such as BALB/c mice. The migration of cells in the immune response to L. major is regulated by chemokines and their receptors. The chemokine receptor CCR7 is expressed on activated DCs and naïve T cells, allowing them to migrate to the correct micro-anatomical positions within secondary lymphoid organs. While there have been many studies on the function of CCR7 during homeostasis or using model antigens, there are very few studies on the role of CCR7 during infection. In this study, we show that B6.CCR7^-/- mice were unable to resolve the lesion and developed a chronic disease. The composition of the local infiltrate at the lesion was significantly skewed toward neutrophils while the proportion of CCR2⁺ monocytes was reduced. Furthermore, a greater percentage of CCR2⁺ monocytes expressed CCR7 in the footpad than in the lymph node or spleen of B6.WT mice. We also found an increased percentage of regulatory T cells in the draining lymph node of B6.CCR7^-/- mice throughout infection. Additionally, the cytokine milieu of the lymph node showed a Th2 bias, rather than the resistant Th1 phenotype. This data shows that CCR7 is required for a protective immune response to intracellular L. major infection.

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.

Regulatory T cells reduce acute lung injury fibroproliferation by decreasing fibrocyte recruitment

Acute lung injury (ALI) causes significant morbidity and mortality. Fibroproliferation in ALI results in worse outcomes, but the mechanisms governing fibroproliferation remain poorly understood. Regulatory T cells (Tregs) are important in lung injury resolution. Their role in fibroproliferation is unknown. We sought to identify the role of Tregs in ALI fibroproliferation, using a murine model of lung injury. Wild-type (WT) and lymphocyte-deficient Rag-1(-/-) mice received intratracheal LPS. Fibroproliferation was characterized by histology and the measurement of lung collagen. Lung fibrocytes were measured by flow cytometry. To dissect the role of Tregs in fibroproliferation, Rag-1(-/-) mice received CD4(+)CD25(+) (Tregs) or CD4(+)CD25(-) Tcells (non-Tregs) at the time of LPS injury. To define the role of the chemokine (C-X-C motif) ligand 12 (CXCL12)-CXCR4 pathway in ALI fibroproliferation, Rag-1(-/-) mice were treated with the CXCR4 antagonist AMD3100 to block fibrocyte recruitment. WT and Rag-1(-/-) mice demonstrated significant collagen deposition on Day 3 after LPS. WT mice exhibited the clearance of collagen, but Rag-1(-/-) mice developed persistent fibrosis. This fibrosis was mediated by the sustained epithelial expression of CXCL12 (or stromal cell-derived factor 1 [SDF-1]) that led to increased fibrocyte recruitment. The adoptive transfer of Tregs resolved fibroproliferation by decreasing CXCL12 expression and subsequent fibrocyte recruitment. Blockade of the CXCL12-CXCR4 axis with AMD3100 also decreased lung fibrocytes and fibroproliferation. These results indicate a central role for Tregs in the resolution of ALI fibroproliferation by reducing fibrocyte recruitment along the CXCL12-CXCR4 axis. A dissection of the role of Tregs in ALI fibroproliferation may inform the design of new therapeutic tools for patients with ALI.

Semaphorin 7a+ regulatory T cells are associated with progressive idiopathic pulmonary fibrosis and are implicated in transforming growth factor-β1-induced pulmonary fibrosis

RATIONALE

Lymphocytes are increasingly associated with idiopathic pulmonary fibrosis (IPF). Semaphorin 7a (Sema 7a) participates in lymphocyte activation.

OBJECTIVES

To define the relationship between Sema 7a and lymphocytes in IPF.

METHODS

We characterized the significance of Sema 7a+ lymphocytes in humans with IPF and in a mouse model of lung fibrosis caused by lung-targeted, transgenic overexpression of TGF-β1. We determined the site of Sema 7a expression in human and murine lungs and circulation and used adoptive transfer approaches to define the relevance of lymphocytes coexpressing Sema7a and the markers CD19, CD4, or CD4+CD25+FoxP3+ in TGF-β1-induced murine lung fibrosis.

MEASUREMENTS AND MAIN RESULTS

Subjects with IPF show expression of Sema 7a on lung CD4+ cells and circulating CD4+ or CD19+ cells. Sema 7a expression is increased on CD4+ cells and CD4+CD25+FoxP3+ regulatory T cells, but not CD19+ cells, in subjects with progressive IPF. Sema 7a is expressed on lymphocytes expressing CD4 but not CD19 in the lungs and spleen of TGF-β1-transgenic mice. Sema 7a expressing bone marrow-derived cells induce lung fibrosis and alter the production of T-cell mediators, including IFN-γ, IL-4, IL-17A, and IL-10. These effects require CD4 but not CD19. In comparison to Sema 7a-CD4+CD25+FoxP3+ cells, Sema7a+CD4+CD25+FoxP3+ cells exhibit reduced expression of regulatory genes such as IL-10, and adoptive transfer of these cells induces fibrosis and remodeling in the TGF-β1-exposed murine lung.

CONCLUSIONS

Sema 7a+CD4+CD25+FoxP3+ regulatory T cells are associated with disease progression in subjects with IPF and induce fibrosis in the TGF-β1-exposed murine lung.

Differential role of regulatory T cells in early and late stages of pulmonary fibrosis

Regulatory T cells (Tregs) are a specific subset of T lymphocytes that regulate the function of other subsets of lymphocytes. Contradictory results have been reported regarding the role of Tregs in lung fibrosis. We wished to clarify the role of Tregs in the early and late stages of bleomycin-induced lung fibrosis in mice by depleting them with anti-CD25+ antibody (PC61). Mice treated with PC61 in early stages had significantly decreased number of CD4+CD25+ T cells compared to mice treated with the isotype control. The number of inflammatory cells, the concentrations of collagen, TGFβ1, the content of collagen and hydroxyproline in lung tissue were significantly reduced in PC61-treated mice compared to mice treated with the isotype control group. Pathological examination of the lung also disclosed reduced fibrotic changes and decreased fibrosis score in the PC61 group compared to control group. By contrast, mice treated with PC61 in late stages of the disease showed more infiltration of inflammatory cells and higher fibrotic score and hydroxyproline content in the lungs than mice treated with the isotype control. Our results suggest that Tregs play a detrimental role in early stages but protective role in late stages of pulmonary fibrosis in mice.

Cytokine-like factor 1 gene expression is enriched in idiopathic pulmonary fibrosis and drives the accumulation of CD4+ T cells in murine lungs: evidence for an antifibrotic role in bleomycin injury

Idiopathic pulmonary fibrosis (IPF) is a progressive and typically fatal lung disease. To gain insight into the pathogenesis of IPF, we reanalyzed our previously published gene expression data profiling IPF lungs. Cytokine receptor-like factor 1 (CRLF1) was among the most highly up-regulated genes in IPF lungs, compared with normal controls. The protein product (CLF-1) and its partner, cardiotrophin-like cytokine (CLC), function as members of the interleukin 6 (IL-6) family of cytokines. Because of earlier work implicating IL-6 family members in IPF pathogenesis, we tested whether CLF-1 expression contributes to inflammation in experimental pulmonary fibrosis. In IPF, we detected CLF-1 expression in both type II alveolar epithelial cells and macrophages. We found that the receptor for CLF-1/CLC signaling, ciliary neurotrophic factor receptor (CNTFR), was expressed only in type II alveolar epithelial cells. Administration of CLF-1/CLC to both uninjured and bleomycin-injured mice led to the pulmonary accumulation of CD4(+) T cells. We also found that CLF-1/CLC administration increased inflammation but decreased pulmonary fibrosis. CLF-1/CLC leads to significantly enriched expression of T-cell-derived chemokines and cytokines, including the antifibrotic cytokine interferon-γ. We propose that, in IPF, CLF-1 is a selective stimulus of type II alveolar epithelial cells and may potentially drive an antifibrotic response by augmenting both T-helper-1-driven and T-regulatory-cell-driven inflammatory responses in the lung.

Pulmonary fibrosis in response to environmental cues and molecular targets involved in its pathogenesis

Chronic lung injury resulting from a variety of different causes is frequently associated with the develop ment of pulmonary fibrosis in humans. Although the etiology of pulmonary fibrosis is generally unknown, several sources of evidence support the hypothesis that a number of environmental and occupational agents play an etiologic role in the pathogenesis of this disease. The agents discussed in this review include beryllium, nylon flock, textile printing aerosols, polyvinyl chloride and didecyldimethylammonium chloride. The authors also describe a variety of animal models, including genetically modified mice, in order to investigate the molecular mechanism of pulmonary fibrosis, focusing on chemokine receptors, regulatory T cells and transforming growth factor-β and bone morphogenetic protein signaling. Overall, we propose the concept of toxicological pulmonary fibrosis as a lung disease induced in response to environmental cues.