title: [Alveolitis in hypersensitivity pneumopathies].
abstract: In the pathogenesis of hypersensitivity pneumonitis several immune mechanisms are in play. The initial phase appears to be an immune complex reaction occurring 4 to 8 hours after antigen inhalation, and is characterized by an early increase in neutrophils in the alveolar washing and histopathologically there are oedema, neutrophil infiltration in the alveolar walls, and vasculitis. After 12 hours and for several days there is a cell mediated immune response and the alveolitis consists of cytotoxic cells and suppressor cells whose target is perhaps to modulate the diminution of the B cell response in the production of antibodies by plasma cells. During this phase the lymphocytes of CD8 positive phenotype, the NK cells and occasionally some plasma cells are increased in the alveolar lavage. The characteristic histological appearance is a mononuclear infiltrate predominantly of lymphocytes and some plasma cells and foamy macrophages. After several weeks and for several months a delayed hypersensitivity reaction may lead to a discrete increase in the CD4 cells in the broncho-alveolar lavage and the formation of granulomas. Finally after several months and for several years the repeated immunological activity and damage to the alveolar wall leads to the secretion of proteolytic enzymes and to growth factors to attract fibroblasts leading to pulmonary fibrosis and to a honeycomb lung with a concomitant increase in alveolar neutrophils as in other diseases characterised by pulmonary fibrosis.
authors.affiliation: Abteilung Pneumologie/Allergologie, Ruhrlandklinik, Essen-Heidhausen, RFA.
authors.forename: U
authors.initials: U
authors.lastname: Costabel
mesh_terms: D000542:Alveolitis, Extrinsic Allergic / Q000175:diagnosis / Q000276:immunology; D001992:Bronchoalveolar Lavage Fluid; D006801:Humans; D008214:Lymphocytes / Q000145:classification / Q000276:immunology; D008264:Macrophages / Q000276:immunology; D011379:Prognosis
vernacular_title: L'alvéolite dans les pneumopathies d'hypersensibilité.