Complete clarification of a case of farmer's lung.

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.