Detection of antigen-specific antibodies on lung tissue in a patient with hypersensitivity pneumonitis

A patient with hypersensitivity pneumonitis showed positive Ouchterlony's immunodiffusion tests against pigeon faecal extract, Cephalosporium and Pullularia antigens. Deposits of immunoglobulins-IgG and IgM antibodies-were detected in a subendothelial position in arterial and venous vessels and on alveolar macrophages in the lung tissue. The IgG deposits in blood vessels belonged to IgG1, IgG2 and IgG3 subclasses and the absorbed IgG on alveolar macrophages to all IgG subclasses. The detection of allergen specific antibodies in lung tissue was made by indirect immunofluorescent staining with FITC conjugated antigen extracts from pigeon faeces and demonstrated the aetiology of this hypersensitivity pneumonitis.