title: Hypersensitivity pneumonitis: an immunopathology review.
abstract: BACKGROUND
  Hypersensitivity pneumonitis (HSP) is an immunologically mediated alveolar and interstitial lung disease caused by repeated inhalation of organic dusts and some occupational agents.
  
  
  OBJECTIVE
  The pathogenesis of HSP is uncertain. A number of unexplained features of HSP remain, namely (1) why do so few exposed individuals develop clinical HSP, (2) what triggers an acute episode after prolonged periods of previous sensitization, and (3) what leads to disease progression. This article considers these issues and aims to discuss and clarify current concepts in pathogenesis.
  
  
  METHODS
  Pertinent literature review in conjunction with the author's personal interpretive opinion.
  
  
  CONCLUSIONS
  Current data suggest that individuals with a T(H)1 dominant response are likely to develop clinical disease. There is also some evidence that genetic factors such as polymorphisms in the major histocompatibility complex, tumor necrosis factor alpha, and tissue inhibitor of metalloproteinase 3 are associated with the development of or resistance to the disease.
authors.affiliation: Department of Pathology, University of Massachusetts Medical School, Worcester, USA. wodab@ummhc.org
authors.forename: Bruce A
authors.initials: BA
authors.lastname: Woda
mesh_terms: D000542:Alveolitis, Extrinsic Allergic / Q000276:immunology* / Q000473:pathology*; D020022:Genetic Predisposition to Disease; D006801:Humans; D007694:Killer Cells, Natural / Q000276:immunology; D008168:Lung / Q000276:immunology / Q000473:pathology; D016176:T-Lymphocyte Subsets / Q000276:immunology; D018417:Th1 Cells / Q000276:immunology