ABSTRACT
Pulmonary fibrosis is the replacement of lung architecture with collagenous extracellular matrix, and is a frequent consequence of chronic inflammation. Fibrosis affects primarily the alveolar structures of the lung in the interstitial lung diseases (ILDs), a group of life-threatening disorders with150 known causes or associations. ILD may be caused by inhaled particles such as asbestos or silica, by inhaled gases such as nitrogen dioxide, by xenobiotics such as the chemotherapeutic agent bleomycin, by systemic autoimmune disease such as scleroderma, by the reaction to aeroallergens such as fungal spores or to infectious agents such as mycobacteria and viruses, or by as yet undefined environmental agents and/or predisposing genetic factors. In most individual patients the cause is impossible to determine. The disease process is classified based on a combination of histolic appearance, which includes division into nongranulomatous and granulomatous inflammatory processes, and cause, if a particular cause is known or likely. The most prevalent ILDs in the developed world are idiopathic pulmonary fibrosis (IPF), occupationally induced fibrosis caused by particle inhalation, and sarcoidosis, a multisystem idiopathic granulomatous disease (1). Tuberculosis, the sec-
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ond leading infectious cause of death in the world (2), involves a granulomatous and progressive fibrotic reaction to Mycobacterium tuberculosis, and tissue fibrosis is an important component of the pathophysiology of the disease. The cell biology of tissue remodeling in the major fibrotic lung diseases/disorders shows some similarities, and altered proteoglycan metabolism is central to each of them.
