ALVEOLAR MACROPHAGE CYTOKINE AND GROWTH-FACTOR PRODUCTION IN A RAT MODEL OF CROCIDOLITE-INDUCED PULMONARY INFLAMMATION AND FIBROSIS

The present study was undertaken to further define the role of alveola r macrophages (AM) in the pulmonary response to crocidolite fibers. Br iefly, groups of 4 male F344 rats were intratracheally instilled with saline or saline suspensions of crocidolite at 2 or 20 mg/kg body weig ht. Animals were sacrificed 3, 7, 14, and 28 d after exposure and the lung response was characterized by analysis of bronchoalveolar lavage fluid (BALF) for markers of lung injury and inflammation. AM obtained in BALF were cultured and their production of the pro-inflammatory cyt okines, tumor necrosis factor alpha (TNF alpha), and interleukin-1 (IL -1) were characterized along with fibronectin, a protein known to stim ulate fibroblast migration and proliferation. Lung hydroxyproline cont ent was determined 28 d after exposure and lung histopathology was cha racterized on d 28 and 90 after exposure. Crocidolite instillation res ulted in transient dose-related pulmonary inflammation as evidenced by increased numbers of BALF neutrophils at the low dose and neutrophils , macrophages, and lymphocytes at the high dose. Cytotoxicity and incr eased permeability were demonstrated by increased levels of BALF lacta te dehydrogenase (LDH) and total protein, respectively. AM TNF alpha a nd IL-1 production were increased only at the high crocidolite dose. T his cytokine response was greatest at d 3 and decreased thereafter. AM TNF alpha and IL-1 release were positively correlated with the increa sed BALF neutrophils. In contrast to TNF alpha and IL-1, AM fibronecti n release was increased at both the low and high doses, with the magni tude of response increasing over time. Consistent with previous acute asbestos inhalation studies, histopathology revealed inflammation loca lized at the level of the terminal bronchioles and alveolar ducts. Fib rosis was demonstrated at both doses by increased trichrome staining o f lung tissue sections. Only the high dose resulted in a detectable in crease in lung hydroxyproline. Given the bioactivities of TNF alpha, I L-1, and fibronectin, their increased production after crocidolite exp osure indicates they contribute to the pulmonary inflammation and fibr osis occurring with this mineral fiber. In addition, the correlation o f increased AM TNF alpha and IL-1 production with increased BALF neutr ophils supports a role for these cytokines in crocidolite-induced infl ammatory cell recruitment. Lastly, association of a persistent increas e in AM fibronectin production with an eventual increase in lung colla gen deposition extends the growing database indicating this response i s a predictive marker of pulmonary fibrosis.