Role of alveolar macrophage- and lung T cell-derived mediators in pulmonary sarcoidosis

Pulmonary manifestations of rheumatologic diseases

PURPOSE OF REVIEW

The present review intends to provide an overview of the diversity and complexity of pulmonary manifestations of rheumatologic diseases and gaps in knowledge to effectively manage them.

RECENT FINDINGS

Diffuse lung disease in children with rheumatologic diseases represents a heterogeneous group of autoimmune disorders. Despite their significant morbidity and mortality, we have limited understanding about their pathogenesis. Here, we provide an overview of the pathophysiology and current management approach of these disorders, highlighting tools which assist with diagnosis, risk stratification and therapy. In this context, we address the need to develop a standardized approach to diagnose at-risk patients with rheumatologic disease and to predict their progression and the need to develop robust studies which evaluate the factors and interventions that influence pulmonary disease outcome.

SUMMARY

Diffuse lung disease in children with rheumatologic diseases represents a heterogeneous group of severe autoimmune disorders. By adopting a collaborative research approach among multicenters to help diagnose, risk stratify, and understand disease progression, effective management decisions can be optimized to improve clinical outcome.

Macrophage-derived biomarkers of idiopathic pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is a severe, rapidly progressive diffuse lung disease. Several pathogenetic mechanisms have been hypothesized on the basis of the fibrotic lung damage occurring in this disease, and a potential profibrotic role of activated alveolar macrophages and their mediators in the pathogenesis of IPF was recently documented. This paper focuses on recent literature on potential biomarkers of IPF derived from activated alveolar macrophages. Biomarker discovery and clinical application are a recent topic of interest in the field of interstitial lung diseases (ILDs). Cytokines, CC-chemokines, and other macrophage-produced mediators are the most promising prognostic biomarkers. Many molecules have been proposed in the literature as potential biomarker of IPF; however, a rigorous validation is needed to confirm their clinical utility.

A vicious circle of alveolar macrophages and fibroblasts perpetuates pulmonary fibrosis via CCL18

RATIONALE

Recently, models of macrophage activation have been revised. Macrophages stimulated with Th2 cytokines have been classified as alternatively activated.

OBJECTIVES

This article examines the expression and regulation of CC chemokine ligand 18 (CCL18), a marker of alternative activation, by human alveolar macrophages (AMs).

METHODS

AM were obtained from bronchoalveolar lavage (BAL) fluid of patients with idiopathic pulmonary fibrosis, sarcoidosis, or hypersensitivity pneumonitis (n = 69) and healthy volunteers (n = 22). Expression of CCL18 was determined by quantitative reverse transcriptase-polymerase chain reaction, in situ hybridization, flow cytometry, and immunohistochemistry, respectively.

MEASUREMENTS AND MAIN RESULTS

Spontaneous CCL18 production by BAL-derived cells was markedly increased in patients with pulmonary fibrosis and correlated negatively with pulmonary function test parameters. CCL18 gene expression and protein production were up-regulated in normal AMs after Th2 cytokine stimulation and/or coculture with human lung fibroblasts. Native collagen significantly up-regulated CCL18 expression in normal AMs activated with Th2 cytokines via a mechanism mediated by beta2-integrin/ scavenger receptor(s). Culture supernatants of AMs from patients with idiopathic pulmonary fibrosis increased collagen production by normal lung fibroblasts partly mediated via CCL18.

CONCLUSIONS

Our findings suggest that AMs from patients with pulmonary fibrosis disclose a phenotype of alternative activation and might be a part of a positive feedback loop with lung fibroblasts perpetuating fibrotic processes.

Interferon-induced granulomatous lung disease

PURPOSE OF REVIEW

Interferon therapy can induce or exacerbate sarcoidosis. With the increasing use of interferons it is highly likely that more cases of sarcoidosis will be encountered by clinicians. We describe three unusual cases of interferon-induced sarcoidosis and review the most recent relevant literature on this subject.

RECENT FINDINGS

Interferons, on account of their antiviral antigrowth and immunomodulatory effects, are used to treat various internal and dermatological diseases. Exogenously administered interferons stimulate the Th-1 response, which plays a major role in granuloma formation. In most of the patients with interferon-induced sarcoidosis, the disease subsides when interferon is discontinued. Occasionally, treatment with corticosteroids may become necessary.

SUMMARY

Interferon therapy can induce or exacerbate sarcoidosis, the disease disappears when interferon is discontinued, sometimes treatment with corticosteroids is required.

Interferon-alpha therapy associated with the development of sarcoidosis

Interferons (IFNs) have been implicated in the pathogenesis of sarcoidosis. In particular, IFN-gamma has been linked to pulmonary macrophage activation, a characteristic feature of sarcoidosis. IFN-alpha is now being administered therapeutically in a variety of conditions. To date, IFN-alpha has not been implicated in the pathogenesis of sarcoidosis. We report the case of a 50-year-old woman who developed sarcoidosis while being treated with IFN-alpha for chronic myelogenous leukemia. Her disease activity correlated with the dosage of IFN-alpha. We speculate that the immunomodulatory effects of IFN-alpha triggered clinical manifestations of sarcoidosis in this patient.

Human alveolar macrophages are markedly deficient in REF-1 and AP-1 DNA binding activity

Although many functions of human alveolar macrophages are altered compared with their precursor cell, the blood monocyte (monocyte), the reason(s) for these functional changes have not been determined. We recently reported that human alveolar macrophages do not express AP-1 DNA binding activity (Monick, M. M., Carter, A. B., Gudmundsson, G., Geist, L. J., and Hunninghake, G. W. (1998) Am. J. Physiol. 275, L389-L397). To determine why alveolar macrophages do not express AP-1 DNA binding activity, we first showed that there was not a decrease in expression of the FOS and JUN proteins that make up the AP-1 complex. There was, however, a significant difference in the amounts of the nuclear protein, REF-1 (which regulates AP-1 DNA binding by altering the redox status of FOS and JUN proteins), in alveolar macrophages compared with monocytes. In addition, in vitro differentiation of monocytes to a macrophage-like cell resulted in decreased amounts of REF-1. Finally, addition of REF-1 from activated monocytes to alveolar macrophage nuclear proteins resulted in a marked increase in AP-1 DNA binding. These studies strongly suggest that the process of differentiation of monocytes into alveolar macrophages is associated with a loss of REF-1 and AP-1 activity. This observation may explain, in part, some of the functional differences observed for alveolar macrophages compared with monocytes.

Relative release of interleukin-1 beta and interleukin-1 receptor antagonist by alveolar macrophages. A study in asbestos-induced lung disease, sarcoidosis, and idiopathic pulmonary fibrosis

We examined the influence of untreated interstitial lung disease (ILD) on the in vitro release of interleukin-1 beta (IL-1 beta) and interleukin-1 receptor antagonist (IL-Ira) from alveolar macrophages (AM); AM were harvested from normal volunteers, ILD patients, and patients with asbestos-related pleural disease but no ILD. AM were cultured for 24 h and assays for IL-1 beta and IL-1ra were done using sensitive and specific enzyme-linked immunosorbent assay. A greater amount of IL-1 beta was detected in AM supernatants from asbestosis, sarcoidosis, and IPF patients than in those from normal subjects. The IL-1 beta:IL-1ra ratio (IL-1 beta activity index [IL-1AI]) was significantly lower in supernatants of normal macrophages compared with macrophage supernatants from individuals with ILD. The IL-1AI correlated with bronchoalveolar lavage cellularity, a marker of disease activity. Current smoking was associated with lower IL-1 beta and IL-1ra release in ILD. The IL-1AI is a convenient method for comparison of IL-1 beta activity between patient populations.

Peripolesis in alveolar sarcoidosis

We observed that in bronchoalveolar lavages (BAL) of patients with active sarcoidosis (SARC) a mononuclear cell infiltrate is present that often contains clusters consisting of lymphocytes adhering to a macrophage. In order to investigate what kind of cellular interactions are involved in such a process, cell suspensions obtained from BAL of patients with SARC or extrinsic allergic alveolitis (EAA) were cultured for 1 to 2 days, during which time lapse cinematography was applied. We were able to show that such clusters consist of lymphocytes gathered around a macrophage. This is known as peripolesis. Peripolesis, as observed in our BAL, could last for some minutes or for some hours during which time a number of lymphocytes were moving around a single alveolar macrophage, without losing contact with the macrophage. Short interactions were mostly observed in EAA, whereas SARC was characterized by long periods of lymphocyte-macrophage cooperation. We also found a correlation between the time-dependent peripolesis t > 30 min/t < 30 min and the CD4/CD8 ratio. Although the precise mechanisms of peripolesis are not well understood, some interactions between lymphocytes and macrophages have now become more comprehensive.

Synergism between interleukin-1 beta and interferon-gamma, an inducer of nitric oxide synthase, in rat lung fibroblasts

An L-arginine-dependent pathway, by which L-arginine is metabolised to citrulline and nitrogen oxides, has been recently identified in some cell types. In cultured rat lung fibroblasts the presence of L-arginine was necessary for the production of nitrite to be induced by rat recombinant interferon-gamma and synergistically enhanced by lipopolysaccharide and interleukin-1 beta. Lipopolysaccharide and interleukin-1 beta did not induce nitrite biosynthesis by themselves. Biosynthesis was apparently dependent on tetrahydrobiopterin, since it could be blocked by diaminohydroxypyrimidine, an inhibitor of tetrahydrobiopterin synthesis. Dexamethasone blocked nitrite production by a receptor-mediated mechanism. These data indicate that rat lung fibroblasts express an L-arginine-dependent nitric oxide synthase which can be induced by some mediators of inflammation.

Immunopathology of vitreous and retinochoroidal biopsy in posterior uveitis

The authors used immunopathologic techniques to study vitreous and/or retinochoroidal biopsies from 23 patients with posterior uveitis unresponsive to conventional therapy or who had developed significant complications despite therapy. Results indicated that during active uveitis from many causes, T-helper cells predominated in the vitreous and retinochoroidal biopsies. Monocytes were not prominent constituents except in several cases of granulomatous etiology (e.g., syphilis and acute retinal necrosis). Class II major histocompatibility complex (MHC) antigens were increased on the retinal vascular endothelium, implicating an important role for these cells in the local cellular immune response. These results may be of great importance in our understanding of uveitis, as well as being helpful in categorizing posterior uveitis, permitting appropriate therapy to be given.

The ultrastructure of epithelial cells of the distal lung

This review has focused on the structural and functional characteristics of those epithelial cells that line the walls of the lower respiratory bronchioles, alveolar ducts, and alveoli. In all, five cells types were considered: Clara cells, types I, II, and III pneumocytes, and alveolar macrophages. In addition, a very brief mention of the structure and influence of the basement membrane in alveolar development and repair was included, as well as a brief review of the role of epithelial cells in response to selected deleterious influences. No attempt was made to extend this review to cover the structure and functions of the epithelial lining of the conducting portions of the respiratory system, or the exciting and expanding complexities and interrelationships of the septal stroma. Since the volume of literature encircling this subject has virtually exploded during the last 15 years, it becomes almost impossible to review all reports. However, attempts were made to be selective in citations. Insofar as future developments are concerned, much remains to be understood concerning (1) the responses of all cell types to cytotoxic influences, including their respective abilities to repair induced damage, (2) cell-cell and cell-extracellular matrix relationships in response to injury, (3) the uniqueness of the basement membrane in the lung in controlling permeability and gaseous exchange, (4) the role(s) of alveolar macrophages in response to injury and their relationships to the septal macrophage population, (5) the aberrations in the respective cell types that can give rise to neoplastic growth, and (6) the role of the immune system in responding to the general defense of the lung. Indeed much has been learned in the past 2 decades, and it is expected that a review of this sort 1 or 2 decades hence will elucidate many of the functions and structural modifications of the lung.