<unk>  is the scarring of lung tissue (beginning around terminal bronchioles and alveolar ducts and extending into the alveolar walls) resulting from the inhalation of asbestos fibers. There are two types of fibers: amphibole (thin and straight) and serpentine (curly). All forms of asbestos fibers are responsible for human disease as they are able to penetrate deeply into the lungs. When such fibers reach the alveoli (air sacs) in the lung, where oxygen is transferred into the blood, the foreign bodies (asbestos fibers) cause the activation of the lungs' local immune system and provoke an inflammatory reaction dominated by lung macrophages that respond to chemotactic factors activated by the fibers. This inflammatory reaction can be described as chronic rather than acute, with a slow ongoing progression of the immune system attempting to eliminate the foreign fibers. Macrophages phagocytose (ingest) the fibers and stimulate fibroblasts to deposit connective tissue. Due to the asbestos fibers' natural resistance to digestion, some macrophages are killed and others release inflammatory chemical signals, attracting further lung macrophages and fibrolastic cells that synthesize fibrous scar tissue, which eventually becomes diffuse and can progress in heavily exposed individuals. This tissue can be seen microscopically soon after exposure in animal models. Some asbestos fibers become layered by an iron-containing proteinaceous material (ferruginous body) in cases of heavy exposure where about 10% of the fibers become coated. Most inhaled asbestos fibers remain uncoated. About 20% of the inhaled fibers are transported by cytoskeletal components of the alveolar epithelium to the interstitial compartment of the lung where they interact with macrophages and mesenchymal cells. The cytokines, transforming growth factor beta and tumor necrosis factor alpha, appear to play major roles in the development of scarring inasmuch as the process can be blocked in animal models by preventing the expression of the growth factors. The result is fibrosis in the interstitial space, thus<unk> . This fibrotic scarring causes alveolar walls to thicken, which reduces elasticity and gas diffusion, reducing oxygen transfer to the blood as well as the removal of carbon dioxide. This can result in shortness of breath, a common symptom exhibited by individuals with<unk> . Those with<unk>  may be more vulnerable to tumor growth (mesothelioma) because asbestos decreases the cytotoxicity of natural killer cells and impairs the functioning of T helper cells, which detect abnormal cell growth.
Asbestosis
Bronchiectasis
Silicosis
Coalworker's pneumoconiosis
Asbestos-related diseases
Organic dust toxic syndrome
Tuberculosis
Occupational lung disease