Focal interstitial CC chemokine receptor 7 (CCR7) expression in idiopathic interstitial pneumonia

The Chemokine System as a Key Regulator of Pulmonary Fibrosis: Converging Pathways in Human Idiopathic Pulmonary Fibrosis (IPF) and the Bleomycin-Induced Lung Fibrosis Model in Mice

Idiopathic pulmonary fibrosis (IPF) is a chronic and lethal interstitial lung disease (ILD) of unknown origin, characterized by limited treatment efficacy and a fibroproliferative nature. It is marked by excessive extracellular matrix deposition in the pulmonary parenchyma, leading to progressive lung volume decline and impaired gas exchange. The chemokine system, a network of proteins involved in cellular communication with diverse biological functions, plays a crucial role in various respiratory diseases. Chemokine receptors trigger the activation, proliferation, and migration of lung-resident cells, including pneumocytes, endothelial cells, alveolar macrophages, and fibroblasts. Around 50 chemokines can potentially interact with 20 receptors, expressed by both leukocytes and non-leukocytes such as tissue parenchyma cells, contributing to processes such as leukocyte mobilization from the bone marrow, recirculation through lymphoid organs, and tissue influx during inflammation or immune response. This narrative review explores the complexity of the chemokine system in the context of IPF and the bleomycin-induced lung fibrosis mouse model. The goal is to identify specific chemokines and receptors as potential therapeutic targets. Recent progress in understanding the role of the chemokine system during IPF, using experimental models and molecular diagnosis, underscores the complex nature of this system in the context of the disease. Despite advances in experimental models and molecular diagnostics, discovering an effective therapy for IPF remains a significant challenge in both medicine and pharmacology. This work delves into microarray results from lung samples of IPF patients and murine samples at different stages of bleomycin-induced pulmonary fibrosis. By discussing common pathways identified in both IPF and the experimental model, we aim to shed light on potential targets for therapeutic intervention. Dysregulation caused by abnormal chemokine levels observed in IPF lungs may activate multiple targets, suggesting that chemokine signaling plays a central role in maintaining or perpetuating lung fibrogenesis. The highlighted chemokine axes (CCL8-CCR2, CCL19/CCL21-CCR7, CXCL9-CXCR3, CCL3/CCL4/CCL5-CCR5, and CCL20-CCR6) present promising opportunities for advancing IPF treatment research and uncovering new pharmacological targets within the chemokine system.

CC Chemokines in Idiopathic Pulmonary Fibrosis: Pathogenic Role and Therapeutic Potential

Idiopathic pulmonary fibrosis (IPF), characterized by progressive worsening of dyspnea and irreversible decline in lung function, is a chronic and progressive respiratory disease with a poor prognosis. Chronic or repeated lung injury results in inflammation and an excessive injury-repairing response that drives the development of IPF. A number of studies have shown that the development and progression of IPF are associated with dysregulated expression of several chemokines and chemokine receptors, several of which have been used as predictors of IPF outcome. Chemokines of the CC family play significant roles in exacerbating IPF progression by immune cell attraction or fibroblast activation. Modulating levels of detrimental CC chemokines and interrupting the corresponding transduction axis by neutralizing antibodies or antagonists are potential treatment options for IPF. Here, we review the roles of different CC chemokines in the pathogenesis of IPF, and their potential use as biomarkers or therapeutic targets.

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.

Development and Validation of the Prognostic Index Based on Inflammation-Related Gene Analysis in Idiopathic Pulmonary Fibrosis

Background: Historically, idiopathic pulmonary fibrosis (IPF) was considered a chronic inflammation disorder, but this conception was reassessed in the past decades. Our understanding of the role of inflammation in IPF and its association with clinical significance remained incomplete.

Methods: We downloaded mRNA expression data of peripheral blood mononuclear cells (PBMCs) from the Gene Expression Omnibus (GEO) repository. Inflammation-related genes (IRGs) expressed differently between IPF and control (CTRL) were determined. In this study, we systemically analyzed the expression of differently expressed IRGs by comprehensive bioinformatic analysis, and then investigated their potential prognostic values. The related prognostic gene expressions were verified in our cohort.

Results: 110 differently expressed IRGs were identified in this study, including 64 upregulated and 46 downregulated IRGs. Three IRGs (S100A12, CCR7, and TNFSF4) were identified as potential hub genes for prognosis. Those genes were subsequently subjected to the construction of the prognostic models. In the results, IPF patients categorized as high risk demonstrated a poor overall survival rate compared to patients categorized as low risk. Based on this prognostic model, the area under the curve (AUC) of the survival-dependent receiver operator characteristic (ROC) for 1-year, 2-year, and 3-year survival rates was 0.611, 0.695, and 0.681, respectively, in the GSE28042 cohort. These observations were validated in the GSE27957 cohort, confirming the good prognostic effect of this model. The expression of the three genes was validated in our cohort. We also conducted a nomogram based on the three IRGs’ mRNA for quantitative IPF prognosis.

Conclusion: Three IRGs (S100A12, CCR7, and TNFSF4) were identified as potential markers for the prognosis of IPF.

Inflammatory mediators in various molecular pathways involved in the development of pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is a type of interstitial lung disease (ILD) that is marked by scarring of lung tissue, ultimately leading to respiratory failure. The survival rate of IPF is disappointing and to date demonstrates a clinical quandary. The exact etiology of the disease remains under discussion. According to the recent hypothesis, inflammatory mediators cause severe damage to the alveolar epithelium leading to the impairment of the alveolar structure. The role of inflammation in the development of the IPF has been controversial for years. There are two schools of thought regarding the role of inflammation. One group of researchers claims that cell death and fibroblast dysfunction are the primary causes and inflammation is just a secondary cause of IPF. The other group claims inflammation to be the primary cause. Studies using human subjects have also reported inflammation as a critical element in IPF. Inflammatory cytokinesserve amajor rolein commencing theinflammatoryresponse in the lungs. Several cytokines are reported to be involved in different molecular mechanisms underlying IPF, someof which alsocontribute additionally by acting as growth factors. The present review addressed to explore the contribution of various inflammatory cytokines, growth factors, and various other inflammatory molecules activating the major molecular pathways involved during the development of IPF.

Integrated pharmacokinetic, pharmacodynamic and immunogenicity profiling of an anti-CCL21 monoclonal antibody in cynomolgus monkeys

QBP359 is an IgG1 human monoclonal antibody that binds with high affinity to human CCL21, a chemokine hypothesized to play a role in inflammatory disease conditions through activation of resident CCR7-expressing fibroblasts/myofibroblasts. The pharmacokinetics (PK) and pharmacodynamics (PD) of QBP359 in non-human primates were characterized through an integrated approach, combining PK, PD, immunogenicity, immunohistochemistry (IHC) and tissue profiling data from single- and multiple-dose experiments in cynomolgus monkeys. When compared with regular immunoglobulin typical kinetics, faster drug clearance was observed in serum following intravenous administration of 10 mg/kg and 50 mg/kg of QBP359. We have shown by means of PK/PD modeling that clearance of mAb-ligand complex is the most likely explanation for the rapid clearance of QBP359 in cynomolgus monkey. IHC and liquid chromatography mass spectrometry data suggested a high turnover and synthesis rate of CCL21 in tissues. Although lymphoid tissue was expected to accumulate drug due to the high levels of CCL21 present, bioavailability following subcutaneous administration in monkeys was 52%. In human disease states, where CCL21 expression is believed to be expressed at 10-fold higher concentrations compared with cynomolgus monkeys, the PK/PD model of QBP359 and its binding to CCL21 suggested that very large doses requiring frequent administration of mAb would be required to maintain suppression of CCL21 in the clinical setting. This highlights the difficulty in targeting soluble proteins with high synthesis rates.

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.

An official American Thoracic Society/European Respiratory Society statement: Update of the international multidisciplinary classification of the idiopathic interstitial pneumonias

BACKGROUND

In 2002 the American Thoracic Society/European Respiratory Society (ATS/ERS) classification of idiopathic interstitial pneumonias (IIPs) defined seven specific entities, and provided standardized terminology and diagnostic criteria. In addition, the historical "gold standard" of histologic diagnosis was replaced by a multidisciplinary approach. Since 2002 many publications have provided new information about IIPs.

PURPOSE

The objective of this statement is to update the 2002 ATS/ERS classification of IIPs.

METHODS

An international multidisciplinary panel was formed and developed key questions that were addressed through a review of the literature published between 2000 and 2011.

RESULTS

Substantial progress has been made in IIPs since the previous classification. Nonspecific interstitial pneumonia is now better defined. Respiratory bronchiolitis-interstitial lung disease is now commonly diagnosed without surgical biopsy. The clinical course of idiopathic pulmonary fibrosis and nonspecific interstitial pneumonia is recognized to be heterogeneous. Acute exacerbation of IIPs is now well defined. A substantial percentage of patients with IIP are difficult to classify, often due to mixed patterns of lung injury. A classification based on observed disease behavior is proposed for patients who are difficult to classify or for entities with heterogeneity in clinical course. A group of rare entities, including pleuroparenchymal fibroelastosis and rare histologic patterns, is introduced. The rapidly evolving field of molecular markers is reviewed with the intent of promoting additional investigations that may help in determining diagnosis, and potentially prognosis and treatment.

CONCLUSIONS

This update is a supplement to the previous 2002 IIP classification document. It outlines advances in the past decade and potential areas for future investigation.

Detection of herpes simplex virus type-1 in patients with fibrotic lung diseases

The current study intends to investigate i) the incidence of herpes viruses including Herpes Simplex Virus type-1 (HSV-1), Cytomegalovirus (CMV) and Human Herpes Virus -6, -7, -8 (HHV6, HHV7, HHV8) in two biological samples, bronchoalveolar lavage fluid (BALF) and lung tissue biopsy, in different forms of pulmonary fibrosis, and ii) the induction of molecular pathways involved in fibrosis by herpesvirus infection in primary cell cultures. PCR was employed for the detection of CMV, HHV6-8 and HSV-1 DNA in lung specimens (4 controls and 11 IPF specimens) and BALF pellet [6 controls and 20 fibrotic Idiopathic Intestitial Pneumonias (f-IIPs) samples: 13 idiopathic pulmonary fibrosis (IPF) and 7 nonspecific idiopathic interstitial pneumonia (NSIP)] samples. Among all herpesviruses tested, HSV-1 was detected in 1/11 (9%) specimens from IPF lung tissue and in 2/20 (10%) samples of f-IIPs BALF whereas the control group was negative. Primary cell cultures from BALF of patients with IPF and healthy controls were infected in vitro with wild-type HSV-1 virus and Real Time PCR was employed for the detection of gene transcription of specific axes implicated in lung fibrosis. Primary cell cultures were permissive to HSV-1, resulting in an upregulation of the fibrotic growth factors TGFβ1 and FGF, the angiogenetic markers SDF1a, SDF1b, VEGF, FGF and the regulators of tissue wound healing MMP9 and CCR7. Downregulation was noted for the CXCR4 and MMP2 genes, while a different response has been detected in healthy donors regarding the expression of the aforementioned markers. These results implicate for the first time the HSV-1 with Fibrotic Idiopathic Interstitial Pneumonias since the virus presented similar incidence in two different biological samples.

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.

New concepts of IL-10-induced lung fibrosis: fibrocyte recruitment and M2 activation in a CCL2/CCR2 axis

IL-10 is most commonly recognized as an anti-inflammatory cytokine possessing immunosuppressive effects necessary for regulated resolution of proinflammation. However, its role in the development of fibrosis during inflammatory resolution has not been clear. Few prior studies have linked IL-10 with the inhibition of fibrosis principally on the basis of regulating inflammation thought to be driving fibroproliferation. In contrast, in a model of long-term overexpression of IL-10, we observed marked induction of lung fibrosis in mice. The total cell number retrieved by bronchoalveolar lavage (BAL) increased 10-fold in the IL-10 overexpression (IL-10 OE) mice, with significant infiltration of T and B lymphocytes and collagen-producing cells. The presence of increased fibrocytes, isolated from collagenase-digested lungs, was identified by flow cytometry using dual staining of CD45 and collagen 1. Quantitative PCR analysis on an array of chemokine/chemokine receptor genes showed that receptor CCR2 and its ligand, CCL2, were highly upregulated in IL-10 OE mice, suggesting that IL-10-induced fibrocyte recruitment was CCL2/CCR2 specific. Given the prior association of alternatively activated (M(2)) macrophages with development of fibrosis in other disease states, we also examined the effect of IL-10 OE on the M(2) macrophage axis. We observed significantly increased numbers of M(2) macrophages in both BAL and whole lung tissue from the IL-10 OE mice. Administration of rabbit anti-CCL2 antiserum to IL-10 OE mice for three consecutive weeks significantly decreased fibrosis as evidenced by lung hydroxyproline content, compared with mice that received preimmune rabbit serum. These results indicate that overexpression of IL-10 induces fibrosis, in part, by fibrocyte recruitment and M(2) macrophage activation, and likely in a CCL2/CCR2 axis.

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

Background

C-C chemokine receptor (CCR)7 is a regulator of dendritic cell and T cell migration, and its role in tissue wound healing has been investigated in various disease models. We have previously demonstrated that CCR7 and its ligand, chemokine (C-C motif) ligand (CCL)21, modulates wound repair in pulmonary fibrosis (PF) but the mechanism of this is unknown. The objective of this study was to investigate whether the absence of CCR7 protects against bleomycin (BLM)-induced PF. CCR7^-/- mice failed to mount a fibrotic pulmonary response as assessed by histologic collagen staining and quantification by hydroxyproline. We hypothesized that the prominent characteristics of CCR7^-/- mice, including elevated levels of cytokine and chemokine mediators and the presence of bronchus-associated lymphoid tissue (BALT) might be relevant to the protective phenotype.

Results

Pulmonary fibrosis was induced in CCR7^+/+ and CCR7^-/- mice via a single intratracheal injection of BLM. We found that the lung cytokine/chemokine milieu associated with the absence of CCR7 correlated with an increase in BALT, and might be attributable to regulatory T cell (Treg) homeostasis and trafficking within the lungs and lymph nodes. In response to BLM challenge, CCR7^-/- mice exhibited an early, steady increase in lung CD4⁺ T cells and increased CD4⁺ CD25⁺ FoxP3⁺ Tregs in the lungs 21 days after challenge. These findings are consistent with increased lung expression of interleukin-2 and indoleamine 2,3-dioxygenase in CCR7^-/- mice, which promote Treg expansion.

Conclusions

Our study demonstrates that the protective phenotype associated with BLM-treated CCR7^-/- mice correlates with the presence of BALT and the anchoring of Tregs in the lungs of CCR7^-/- mice. These data provide novel evidence to support the further investigation of CCR7-mediated Treg trafficking in the modulation of BLM-induced PF.

Decreased Interstitial FOXP3+ Lymphocytes in Usual Interstitial Pneumonia with Discrepancy of CXCL12/CXCR4 Axis

Regulatory T cells (Treg) play a critical role in immune homeostasis and expansion of Treg is controlled by chemokine receptors. The chemokine CXCL12 and its G-protein-coupled receptor (CXCR4) are involved in the development of idiopathic pulmonary fibrosis (IPF), but the association of Treg with the CXCL12/CXCR4 axis has not been documented. The aim of this study is to determine the distribution and extent of CXCL12/CXCR4 expression in idiopathic type of pulmonary fibrosis, and the relation of Treg expansion in the interstitium of pulmonary fibrosis patients to CXCL12/CXCR4 expression. CXCL12 expression was examined by immunostaining and ELISA in tissue specimens from patients with usual interstitial pneumonia (UIP, n=15), patients with fibrotic non-specific interstitial pneumonia (f-NSIP, n=4), and controls (n=6). CXCR4 expression was examined by in situ hybridization and immunoblotting. Expression of CD45, CD3, CD20, transcription factor forkhead box P3 (FOXP3), and CD25 was assessed by immunostaining. Fibrosis was evaluated by determining the established fibrosis (EF) score. The CXCL12/CXCR4 axis was upregulated in UIP and f-NSIP, and CXCL12 derived from lung tissue attracted CXCR4+ cells. CXCR4+ cells showed a CD3+ cell distribution pattern. The interstitial FOXP3+/CD3+ and CD25+/CD3+ cell ratios were lower in UIP than f-NSIP, but the CXCR4+/ CD3+ cell ratio was not different. The FOXP3+/CD3+ cell ratio and EF score were inversely correlated. These findings suggest that the CXCL12/CXCR4 axis contributes to inflammation in UIP and f-NSIP by promoting the accumulation CXCR4+ lymphocytes, and a decrease of Treg is correlated with the severity of fibrosis in UIP.

Ursodeoxycholic acid exacerbates peginterferon-induced interstitial pneumonia in a patient with hepatitis C

Pegylated interferon alpha combined with ribavirin is currently the standard treatment for hepatitis C virus (HCV) infection. Ursodeoxycholic acid (UDCA) is used as a complementary treatment in patients who are non-responders or who develop severe side effects of this combined therapy. UDCA is generally considered to be a relatively safe drug. However, we recently encountered a patient with chronic hepatitis C in whom interferon-induced interstitial pneumonia was exacerbated by UDCA. This patient responded to initial antiviral therapy with non-pegylated interferon alpha-2b and ribavirin, but hepatitis recurred soon after the end of treatment. A second course of antiviral therapy using peginterferon alpha-2b and ribavirin achieved normalization of serum transaminases and HCV-RNA, but also caused interstitial pneumonia. After discontinuing peginterferon, this side effect was ameliorated. On the other hand, hepatitis relapsed four months later. UDCA treatment was started and serum transaminase levels decreased, but exacerbation of interstitial pneumonia occurred with marked elevation of the serum KL-6 level. To our knowledge, this is the first reported case of peginterferon-induced interstitial pneumonia showing exacerbation due to UDCA therapy.

PSMB2 and RPL32 are suitable denominators to normalize gene expression profiles in bronchoalveolar cells

BACKGROUND

For accuracy of quantitative reverse transcriptase-polymerase chain reaction (qRT-PCR), normalisation with suitable reference genes is required. To date, no reference genes have been validated for expression studies of bronchoalveolar (BAL) cells. The aims of this study were to identify gene(s) with stable mRNA expression in BAL cells irrespective of gender, smoking, BAL cellular composition, lung pathology, treatment; and to assess the influence of reference genes on target gene expression data.

RESULTS

The mRNA expression of ten housekeeping genes (ACTB, ARF1, CANX, G6PD, GAPDH, GPS1, GNB2L1, PSMB2, PSMD2, RPL32) was investigated by qRT-PCR in BAL cells from 71 subjects across a spectrum of lung diseases. The analyses were validated in an independent BAL cohort from 63 sarcoidosis patients and 17 control subjects. A second derivative method was used to calculate expression values (CTt); an equivalence test, applets BestKeeper, geNorm and NormFinder were applied to investigate gene expression stability. Of the investigated genes, PSMB2 (CTt +/- SD, 23.66 +/- 0.86) and RPL32 (18.65 +/- 0.92) were the most stable; both were constantly expressed in BAL samples from parallel investigated cohorts irrespective of evaluated variables. Finally, to demonstrate effect of traditional (ACTB/GAPDH) and novel (PSMB2/RPL32) reference genes as denominators, expression of two cytokines known associated with sarcoidosis was investigated in sarcoid BAL cells. While normalization with PSMB2/RPL32 resulted in elevated IFNG mRNA expression (p = 0.004); no change was observed using GAPDH/ACTB (p > 0.05). CCL2 mRNA up-regulation was observed only when PSMB2/RPL32 were used as denominators (p < 0.03).

CONCLUSION

PSMB2 and RPL32 are, therefore, suitable reference genes to normalize qRT-PCR in BAL cells in sarcoidosis, and other interstitial lung disease.

Fibrocytes are a potential source of lung fibroblasts in idiopathic pulmonary fibrosis

Idiopathic pulmonary fibrosis is characterized by the accumulation of fibroblasts/myofibroblasts and aberrant remodeling of the lung parenchyma. However, the sources of fibroblasts in IPF lungs are unclear. Fibrocytes are circulating progenitors of fibroblasts implicated in wound healing and fibrosis. In this study we evaluated evidence for the presence of fibrocytes in the lung of patients with idiopathic pulmonary fibrosis by immunofluorescence and confocal microscopy. Fibrocytes were identified in tissues in 8 out of 9 fibrotic lungs. Combinations including CXCR4 and a mesenchymal marker stained significantly more fibrocytes/mm(2) of tissue compared with combinations using CD34 or CD45RO with mesenchymal markers: CXCR4/procollagen-I (10.3+/-2.9fibrocytes/mm(2)) and CXCR4/prolyl-4-hydroxylase (4.1+/-3.1), versus CD34/procollagen-I (2.8+/-3.0), CD34/alphaSMA (2.2+/-1.6) and CD45RO/prolyl-4-hydroxylase (1.3+/-1.6); p<0.003. There was a positive correlation between the abundance of fibroblastic foci and the amount of lung fibrocytes (r=0.79; p<0.02). No fibrocytes were identified in normal lungs. The fibrocyte attractant chemokine CXCL12 increased in plasma [median: 2707.5pg/ml (648.1-4884.7) versus 1751.5pg/ml (192.9-2686.0) from healthy controls; p<0.003)] and was detectable in the bronchoalveolar lavage fluid of 40% of the patients but not in controls. In the lung CXCL12 was strongly expressed by alveolar epithelial cells. A negative correlation between plasma levels of CXCL12 with lung diffusing capacity for carbon monoxide (DLCO) (r=-0.56; p<0.03) and oxygen saturation on exercise was found (r=-0.41; p<0.04). These findings indicate that circulating fibrocytes, likely recruited through the CXCR4/CXCL12 axis, may contribute to the expansion of the fibroblast/myofibroblast population in idiopathic pulmonary fibrosis.

Expression of chemokine receptors CCR7 and CCR8 in the CNS during ChREAE

Chemokines and their receptors are important players in organism homeostasis, development and immune response to inflammatory stimuli. It has been recently confirmed that they are also involved in the development of several autoimmune diseases. In this study, we analysed the expression of two recently identified CC chemokine receptors, CCR7 and CCR8, in the central nervous system (CNS) and in peripheral tissues during chronic relapsing experimental autoimmune encephalomyelitis (ChREAE) -- an animal model of the human demyelinating disease multiple sclerosis (MS). We observed upregulation of both chemokine receptors in the CNS during the first and second attacks of ChREAE, whereas disease remission was characterized by a lower expression of those receptors. An analysis of the kinetics of CCR7 and CCR8 expression in the CNS during the first attack of the disease showed a constant increase in the first few days after the onset of clinical signs. This expression correlated with the clinical severity of ChREAE. CCR7-positive mononuclear cells were detected mostly in perivascular inflammatory cuffs in the CNS. In peripheral tissues (the spleen and kidneys) expression of both receptors was not upregulated during active ChREAE. These findings suggest that CCR7 and CCR8 may play a significant role in the pathogenesis of EAE and probably MS.

The role of the fibrocyte, a bone marrow-derived mesenchymal progenitor, in reactive and reparative fibroses

Human fibrocytes are mesenchymal progenitors that exhibit mixed morphological and molecular characteristics of hematopoietic stem cells, monocytes and fibroblasts. They likely represent the obligate intermediate stage of differentiation into mature mesenchymal cells of a bone marrow-derived precursor of the monocyte lineage under permissive conditions. On in vitro stimulation with pro-fibrotic cytokines and growth factors, human fibrocytes produce large quantities of extracellular matrix components and further differentiate into cells identical to the contractile myofibroblasts that emerge at the tissue sites during repair processes and in some fibrotic lesions. Studies in various animal models of wound healing or fibrotic diseases have confirmed the ability of fibrocytes to differentiate into mature mesenchymal cells in vivo and have suggested a causal link between fibrocyte accumulation and ongoing tissue fibrogenesis or vascular remodeling in response to tissue damage or hypoxia. Fibrocytes synthesizing new collagen or acquiring myofibroblast markers have been detected in human hypertrophic scars, in the skin of patients affected by nephrogenic systemic fibrosis, in human atherosclerotic lesions, and in pulmonary diseases characterized by repeated cycles of inflammation and repair, like asthma. The presence of fibrocyte-like cells has been reported in human chronic pancreatitis and chronic cystitis. Similar cells also populate the stroma surrounding human benign tumors. The available data indicate that human fibrocytes serve as a source of mature mesenchymal cells during reparative processes and in fibrotic disorders or stromal reactions predominantly associated with a persistent inflammatory infiltrate or with the selective recruitment of monocytes induced by ischemic changes and tumor development. A deeper understanding of the mechanisms involved in fibrocyte differentiation in these pathological conditions may lead to the development of novel therapies for preventing detrimental tissue or vascular remodeling and metastatic progression of invasive tumors.

Circulating progenitor cells in chronic lung disease

Tissue regeneration and repair are fundamental both to recovery of the lung from injury and to the pathology of many chronic lung diseases. There are two potential sources for the adult progenitor cells that participate in this reparative process: resident lung progenitors and bone marrow-derived circulating cells. Bone marrow-derived cells, in particular, have been shown to give rise to airway and alveolar epithelial cells, as well as lung mesenchymal cells. Emerging data have linked specific chemokine ligand-receptor interactions to the recruitment of these cells to the lung and has implicated these cells in chronic lung disorders such as asthma and interstitial lung diseases. In this review, we summarize the current understanding of the biology of adult circulating progenitors as related to lung disease.

Fibrocytes in lung disease

Fibrocytes were first described over a decade ago as a population of cells in circulation with fibroblast-like properties, which were involved in tissue repair. Since that time, we have learned a significant amount about these bone marrow-derived cells, which contribute to wound healing and fibrosis. Fibrocytes express leukocyte markers such as CD34, CD45, and CD13 and also express mesenchymal markers such as pro-collagens I and III, vimentin, and fibronectin. In addition, they have been shown to express the chemokine receptors CXCR4 and CCR7, which appear to be important in cellular trafficking from the vascular to the extravascular compartment. Fibrocytes have been shown to contribute to a number of fibrotic disorders, and here, we review their involvement in lung diseases including pulmonary fibrosis, asthma, and vascular remodeling.

The role of CXC chemokines in pulmonary fibrosis

The CXC chemokine family is a pleiotropic family of cytokines that are involved in promoting the trafficking of various leukocytes, in regulating angiogenesis and vascular remodeling, and in promoting the mobilization and trafficking of mesenchymal progenitor cells such as fibrocytes. These functions of CXC chemokines are important in the pathogenesis of pulmonary fibrosis and other fibroproliferative disorders. In this Review, we discuss the biology of CXC chemokine family members, specifically as it relates to their role in regulating vascular remodeling and trafficking of circulating mesenchymal progenitor cells (also known as fibrocytes) in pulmonary fibrosis.

Therapeutic targeting of CC ligand 21 or CC chemokine receptor 7 abrogates pulmonary fibrosis induced by the adoptive transfer of human pulmonary fibroblasts to immunodeficient mice

Idiopathic interstitial pneumonias (IIPs) are a collection of pulmonary fibrotic diseases of unknown etiopathogenesis. CC chemokine receptor 7 (CCR7) is expressed in IIP biopsies and primary fibroblast lines, but its role in pulmonary fibrosis was not previously examined. To study the in vivo role of CCR7 in a novel model of pulmonary fibrosis, 1.0 x 10(6) primary fibroblasts grown from idiopathic pulmonary fibrosis/usual interstitial pneumonia, nonspecific interstitial pneumonia, or histologically normal biopsies were injected intravenously into C.B-17 severe combined immunodeficiency (SCID)/beige (bg) mice. At days 35 and 63 after idiopathic pulmonary fibrosis/usual interstitial pneumonia fibroblast injection, patchy interstitial fibrosis and increased hydroxyproline were present in the lungs of immunodeficient mice. Adoptively transferred nonspecific interstitial pneumonia fibroblasts caused a more diffuse interstitial fibrosis and increased hydroxyproline levels at both times, but injected normal human fibroblasts did not induce interstitial remodeling changes in C.B-17SCID/bg mice. Systemic therapeutic immunoneutralization of either human CCR7 or CC ligand 21, its ligand, significantly attenuated the pulmonary fibrosis in groups of C.B-17SCID/bg mice that received either type of IIP fibroblasts. Thus, the present study demonstrates that pulmonary fibrosis is initiated by the intravenous introduction of primary human fibroblast lines into immunodeficient mice, and this fibrotic response is dependent on the interaction between CC ligand 21 and CCR7.

Gene expression profiling of familial and sporadic interstitial pneumonia

RATIONALE

Idiopathic interstitial pneumonia (IIP) and its familial variants are progressive and largely untreatable disorders with poorly understood molecular mechanisms. Both the genetics and the histologic type of IIP play a role in the etiology and pathogenesis of interstitial lung disease, but transcriptional signatures of these subtypes are unknown.

OBJECTIVES

To evaluate gene expression in the lung tissue of patients with usual interstitial pneumonia or nonspecific interstitial pneumonia that was either familial or nonfamilial in origin, and to compare it with gene expression in normal lung parenchyma.

METHODS

We profiled RNA from the lungs of 16 patients with sporadic IIP, 10 with familial IIP, and 9 normal control subjects on a whole human genome oligonucleotide microarray.

RESULTS

Significant transcriptional differences exist in familial and sporadic IIPs. The genes distinguishing the genetic subtypes belong to the same functional categories as transcripts that distinguish IIP from normal samples. Relevant categories include chemokines and growth factors and their receptors, complement components, genes associated with cell proliferation and death, and genes in the Wnt pathway. The role of the chemokine CXCL12 in disease pathogenesis was confirmed in the murine bleomycin model of lung injury, with C57BL/6(CXCR4+/-) mice demonstrating significantly less collagen deposition than C57BL/6(CXCR4+/+) mice. Whereas substantial differences exist between familial and sporadic IIPs, we identified only minor gene expression changes between usual interstitial pneumonia and nonspecific interstitial pneumonia.

CONCLUSIONS

Taken together, our findings indicate that differences in gene expression profiles between familial and sporadic IIPs may provide clues to the etiology and pathogenesis of IIP.

Airway smooth muscle and mast cell-derived CC chemokine ligand 19 mediate airway smooth muscle migration in asthma

RATIONALE

Airway smooth muscle (ASM) hyperplasia is a feature of asthma, and increases with disease severity. We hypothesized that this results from migration of ASM or progenitors in response to chemokines derived from ASM or mast cells within the ASM bundle.

OBJECTIVES

To examine expression of the chemokine receptor, CC chemokine receptor (CCR) 7, in vivo by ASM in patients with asthma and healthy control subjects, and by primary cultures of ASM and fibroblasts; to define expression of its ligands, CC chemokine ligand (CCL) 19 and CCL21, in bronchial biopsies, and primary cultures of ASM and mast cells; and to investigate CCR7's role in ASM migration and repair.

METHODS

ASM was isolated from bronchoscopy and resection tissue. Receptor and chemokine expression was examined by immunohistochemistry, immunofluorescence, flow cytometry, ELISA, and reverse transcriptase-polymerase chain reaction. CCR7 function was examined by intracellular calcium measurements, chemotaxis, wound healing assays, and measurement of cell proliferation.

MEASUREMENTS AND MAIN RESULTS

ASM, myofibroblasts, and fibroblasts expressed CCR7. CCL19, but not CCL21, was highly expressed in bronchial biopsies by mast cells and vessels in asthma of all severities, ASM in severe disease, and ex vivo ASM and mast cells. ASM CCR7 activation by CCL19-mediated intracellular calcium elevation and concentration-dependent migration, but not proliferation. Importantly, mast cell and ASM-derived CCL19 mediated ASM migration and repair.

CONCLUSIONS

The CCL19/CCR7 axis may play an important role in the development of ASM hyperplasia in asthma.