Copyright ©ERS Journals Ltd 2005 CCR5 expression and CC chemokine levels in idiopathic pulmonary fibrosisDivision of Pulmonary Disease, "Salvatore Maugeri" Foundation, Istituto di Ricovero e Cura a Carattere Scientifico (IRCCS), Scientific Institute of Veruno, Veruno, Italy CORRESPONDENCE: A. Capelli, Divisione di Pneumologia, Fondazione S. Maugeri IRCCS, Istituto Scientifico di Veruno, Veruno (Novara), Italy. Fax: 39 0322884776. E-mail: acapelli@fsm.it Keywords: Bronchoalveolar lavage, CC chemokine, CC chemokine receptor 5, idiopathic pulmonary fibrosis
Received: July 9, 2004
CC chemokines play an important role in the pathogenetic mechanisms of interstitial lung disease, while a downregulation of CC chemokine receptor (CCR)5 in the fibrotic stages of sarcoidosis has been observed. To evaluate the involvement of CC chemokines and the expression of CCR5 in idiopathic pulmonary fibrosis (IPF) and, more specifically, in usual interstitial pneumonia, 35 subjects were studied. CC chemokine ligand (CCL)2, CCL3 and CCL4 levels were measured in the bronchoalveolar lavage fluid (BALF) of 18 nonsmoker control subjects and 17 patients affected by IPF. CCR5 expression was evaluated in alveolar macrophages and lymphocytes. The BALF levels of all chemokines were significantly increased in IPF: median (range) CCL3 1.6 (1.011.1) versus 1.2 (0.03.8) pg·mL1; CCL4 6.2 (1.396.0) versus 3.4 (0.36.8) pg·mL1; and CCL2 60.1 (16.7251.3) versus 4.6 (0.5119.4) pg·mL1. CCL2 levels correlated negatively with the carbon monoxide diffusing capacity of the lung (DL,CO) and arterial oxygen tension. CCR5 expression was significantly reduced in lymphocytes from IPF compared with controls. The CC chemokines investigated are involved in the inflammatory mechanisms of idiopathic pulmonary fibrosis, and the results are in agreement with the hypothesis of a downregulation of the T-helper 1 immunological response in this disease. Idiopathic pulmonary fibrosis (IPF) is a specific form of chronic fibrosing interstitial pneumonia limited to the lung, with the histopathological characteristics of usual interstitial pneumonia (UIP) on lung biopsy 1. The aetiology is unknown. The histological hallmark and chief diagnostic criterion is a heterogeneous appearance at low magnification, with alternating areas of normal lung, interstitial inflammation, fibrosis and honeycomb change 1. Normal repair following lung injury results in the rapid restoration of tissue integrity and function. In contrast to normal repair, chronic inflammation in IPF promotes fibroproliferation and deposition of extracellular matrix, reflecting disregulated and exaggerated tissue repair. A salient feature of chronic inflammation is infiltration by leukocytes, and their recruitment requires intercellular communication between infiltrating leukocytes on the one hand, and the endothelium and resident stromal and parenchymal cells on the other. These events are mediated by the generation of early-response cytokines, such as interleukin (IL)-1 and tumour necrosis factor (TNF), the expression of cell-surface adhesion molecules, and the production of chemotactic molecules, such as chemokines 2.
Originally described as chemotactic factors, chemokines are now known to modulate cytokine production, adhesion molecule expression and mononuclear cell proliferation 3. In animal models of IPF induced by bleomycin, CC chemokines such as CC chemokine ligand (CCL)3 (macrophage inflammatory protein (MIP)-1 No data are available on the role of CCL4 (MIP-1ß) in IPF, but an augmented production of CCL4 by peripheral blood mononuclear cells and increased serum concentrations of this chemokine, together with CCL2 and CCL3, have been observed in systemic sclerosis involving the lung 4.
The balance between two macrophage-derived CC chemokines, CCL3 and CCL4, could potentially be involved in sustaining inflammation and a chronic course in IPF. Both of these chemokines recognise CC chemokine receptor (CCR)5 as a cellular receptor in activated T-lymphocytes and alveolar macrophages 5. Stimulation of CCR5 induces an intracellular biochemical cascade, with increased production and release of IL-2 and interferon (IFN)- In a recent study on pulmonary sarcoidosis, an increase of CCR5 expression was observed in lymphocytes and alveolar macrophages of patients affected by sarcoidosis, but with a downregulation in the advanced stage; an involvement of CCL4 from the earliest phases of the disease was also observed, with an involvement of CCL3 prevalently in the advanced fibrotic stages of sarcoidosis 7. To compare IPF with the advanced stage of sarcoidosis in the present study, the authors measured the levels of CCL3 and CCL4 in bronchoalveolar lavage (BAL) of patients affected by IPF and the expression of their receptor CCR5 in alveolar cells. The BAL fluid (BALF) concentrations of CCL2 and their correlations with the degree of functional impairment were also evaluated. Some results of this study have been previously reported in the form of an abstract 8.
Study population Eighteen healthy, nonsmoker historical controls, who presented also in a previous study by the current authors 7, and 17 patients affected by mildmoderate IPF were studied. IPF was diagnosed on the basis of clinical, functional, radiographic and histological criteria. According to the definition of IPF by the American Thoracic Society and European Respiratory Society international consensus statement, nine patients had histological evidence of UIP at biopsy obtained with thoracotomy or video-assisted thoracoscopy, and eight patients were diagnosed as IPF with transbronchial biopsy and BAL in the presence of all major and minor diagnostic criteria 1. Nine patients were nonsmokers and eight were ex-smokers (for 5 yrs). Treatment with steroid or nonsteroid anti-inflammatory drugs was stopped 3 months before inclusion in the study. None of the subjects had ever been prescribed cytotoxic or immunomodulatory drug therapy before inclusion. Informed consent was obtained from each subject, and the protocol was approved by the Review Board of the Scientific Institute of Veruno, Veruno, Italy.
Pulmonary function tests
Processing of bronchoalveolar lavages
Immunocytochemistry Cytospin preparations of lipopolysaccharide-stimulated mononuclear cells were used as a positive control in each staining run. Negative control slides included cytospin preparations immunostained with mouse monoclonal immunoglobulin G2a (Dako).
Light-microscopic analysis of stained cells was performed at a magnification of x1,000 and a total of
Immunoassay
Statistical analysis
Functional data Table 1
Differential cell counts of BALF The BAL number of total cells was slightly but significantly increased in IPF (200.3x103 cells·mL1 versus 125.1x103 cells·mL1; p<0.05) compared with controls, as shown in table 2
BALF levels of CCL2, CCL3 and CCL4 All the chemokines evaluated were increased in the BALF of IPF patients. The increase of CCL3 (fig. 1
Relationship between functional impairment, BAL characteristics and concentrations of CCL2, CCL3 and CCL4 Since the two groups were significantly different, the current authors analysed the relationship between concentrations of the chemokines and both functional and cellular data within the IPF group alone. With control subjects excluded from the analysis, many statistically significant correlations disappeared. Nevertheless, the increase of CCL2 concentrations in the BALF of patients affected by IPF was correlated with Pa,O2 (p<0.003) and DL,CO (p<0.009), as shown in figure 4 = 0.569, p<0.05, and = 0.608, p<0.02, respectively) and eosinophils ( = 0.600, p<0.03, and = 0.675, p<0.02, respectively).
CCR5-positive cells in BALF The alveolar macrophages of IPF patients and controls expressed the chemokine receptor CCR5 in a similar way, as shown in table 3
The current findings demonstrate increased levels of three CC chemokines, CCL2, CCL3 and CCL4, in the BALF of patients affected by IPF, associated with a decreased expression of cellular receptor CCR5 in lymphocytes. The pathogenesis of IPF or UIP is due to inflammation/injury to the alveolar-capillary wall basement membrane, leading to a loss of type-I epithelial and endothelial cells, proliferation of type-II cells, a loss of alveolar integrity, recruitment and proliferation of stromal cells, and deposition of extracellular matrix and end-stage fibrosis 10. McKee et al. 11 observed that hyaluronan fragments, glycosaminoglycan constituents of the extracellular matrix, are capable of activating macrophages and inducing the expression of genes whose functions are relevant to chronic inflammation, in particular, the chemokine gene family: CCL2, CCL3 and CCL4, cytokine responsive gene-2 and RANTES (regulated on activation, normal T-cell expressed and secreted) 11. The involvement of CC chemokines in the inflammatory events of IPF has been observed in the increased levels of CCL2 and CCL3 in IPF, in the animal fluorescein isothiocyanate (FITC) and bleomycin models 3, 12 and in human studies 13. Using both FITC and bleomycin models in mice, Moore et al. 12 observed that animals with genetically modified CCR2/ were protected from the development of pulmonary fibrosis compared with the wild-type CCR2+/+, even if, in both types of mice, CCL2 levels in BAL were increased. In humans, Suga et al. 13 observed increased levels of CCL2 in the BAL and serum of patients affected by IPF, and demonstrated a relationship between serum levels of CCL2 and the clinical course of interstitial lung disease. The current findings confirm the increased levels of CCL2 in the BAL of patients affected by IPF compared with normal subjects, and reinforce the relationship observed by Suga et al. 13 between this chemokine and the clinical course of the disease, showing a significant correlation also with the degree of functional impairment and, thus, with the severity of the disease.
CCL2 and its receptor CCR2 are involved in fibrosis through the regulation of profibrotic fibroblast-derived cytokine generation and matrix deposition: fibroblasts isolated and cultured from fibrotic granuloma (T-helper (Th)2-type lesion) generated twice as many CCL2, as did similar numbers of fibroblasts from nonfibrotic granuloma (Th1-type lesion) or normal fibroblasts. In addition, stimulation of IL-4, a typical Th2 cytokine, also increases the number of normal fibroblasts expressing CCR2; in contrast, treatment with IFN-
In addition, since the activation of CCR5 induces an increased production of IL-2 and IFN-
Recently, whilst evaluating surgical biopsies, and isolating and culturing primary pulmonary fibroblast lines from UIP, Choi et al. 17 observed an increased expression of CCR5 in these latter cells, but did not evaluate alveolar macrophages and lymphocytes. Interestingly, in the same study, Choi et al. 17 also observed an increase of CCL7 levels in UIP, and reported that this chemokine could bind CCR5 with high affinity without eliciting a functional response and displacing CCR5 agonists. Hence, the presence of high levels of CCL7 could contribute to the reduced activity of CCR5 and, consequently, to the decreased production of IFN- An important role of CCL3 has been observed in the inflammatory process of fibrotic lung diseases and in the bleomycin-induced model of pulmonary fibrosis in mice 3, 19, in which treatment with anti-CCL3 antibody reduced the net lung hydroxyproline content by 49% compared with bleomycin-challenged mice treated with nonimmune serum 20. In a study on sarcoidosis, the current authors observed a different involvement of these CC chemokines during the evolution towards a fibrotic advanced stage 7. When evaluating groups of patients at different stages of sarcoidosis, an involvement of both these CC chemokines was observed: CCL4 from the earliest phases of the disease and CCL3 prevalently in the advanced fibrotic stages of sarcoidosis. In addition, a significant correlation was found between the levels of CCL3 in BAL and neutrophils 7. In the present study, the authors confirmed increased levels of these two chemokines in the BAL of fibrotic patients and, as expected, an increase of the number and percentage of neutrophils, which positively correlate with CCL3 levels in BAL.
Bless et al. 21 observed in rats that CCL4 contributed significantly to the recruitment of neutrophils, and to lung production of TNF- No correlation was found between CCL4 levels and the number or percentage of neutrophils. In fact, in humans, this chemokine is not involved in neutrophil recruitment 23. Finally, viral infection, in particular, herpes virus chronic infection, is one of the hypothetic aetiologies of UIP 15, 22. Lillard et al. 24 observed recently that both CCL3 and CCL4 are not only involved in inflammation, but they also mediate mucosal and systemic adaptive immunity, enhancing the mucosal and serum humoral as well as cellular immune response against infectious diseases, particularly those of a viral origin. CCR5 is a coreceptor for entry of HIV-1 infection in cells, CCL7 is increased in UIP and prevents the binding of R5 strains of HIV 17, while CCL3 and CCL4 are potent inhibitors of M-tropic HIV infection 24, and both, as observed in the present study, are increased in UIP. All these observations could contribute to reinforce the hypothesis of viral involvement in the aetiology of UIP. Therefore, the role and function of chemokines in the inflammation and immunity of pulmonary disease, and, in particular, in the pathogenesis of interstitial lung diseases, is far from being completely clarified. The present data, however, suggest a profibrotic role of CC chemokines in the progression of idiopathic pulmonary fibrosis and contribute, as understanding of the inflammatory mechanism underlying usual interstitial pneumonia/idiopathic pulmonary fibrosis increases, towards the development of possible approaches to challenge fibrogenesis as a means to combat this progressive and fatal disease.
The authors thank R. Allpress for her editorial assistance.
This article has been cited by other articles:
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||