Asbestosis

Asbestosis is a chronic, progressive interstitial lung disease caused by the inhalation and retention of asbestos fibers in the lung parenchyma. Asbestos is a naturally occurring silicate mineral that was widely used in construction, insulation, shipbuilding, automotive brakes, and industrial manufacturing due to its heat resistance, tensile strength, and insulating properties. When asbestos-containing materials are disturbed, microscopic fibers become airborne and can be inhaled deep into the respiratory tract. There are two main fiber types: serpentine fibers (chrysotile, which is curved and more easily cleared) and amphibole fibers (amosite, crocidolite, tremolite, which are straight, needle-like, and more pathogenic). The inhaled fibers penetrate to the terminal bronchioles and alveoli, where alveolar macrophages attempt to engulf them. However, amphibole fibers are too long (greater than 20 micrometers) for complete phagocytosis, a phenomenon called frustrated phagocytosis. The macrophages release reactive oxygen species, proteolytic enzymes, and fibrogenic growth factors (transforming growth factor-beta, platelet-derived growth factor) in an attempt to destroy the fibers. This persistent inflammatory response activates fibroblasts, which deposit excessive collagen in the alveolar interstitium, causing progressive interstitial fibrosis. The fibrosis thickens the...