The diagnostic curriculum to clarify a case of
farmer's lung in a fibrotic stage is presented, including clinical functional tests, X-ray, analysis of cellular elements recovered from bronchioalveolar lavage, determination of precipitating
antibodies in the circulation, histological and immunohistological studies of transbronchial lung biopsies. The patient had precipitating
antibodies against several species of hay molds, especially Micropolyspora faeni, and
immune complex deposition in the lung. Elution experiments on frozen sections of the lung biopsies and subsequent administration of patient's serum- or mold
antigen-specific
antibodies combined with appropriate serum absorption experiments allowed the identification of the relevant
antigen, i.e. M. faeni, in the deposited
immune complexes. The immunohistological analysis of extracellular matrix components revealed an interstitial increase in
procollagen and
collagen type I and an even more pronounced augmentation of
procollagen type III and
fibronectin, i.e. a constellation characteristic for a chronic, active lung
fibrosis that developed on the basis of an
immune complex disease.