Morphology, pathogenesis and classification of interstitial lung diseases

The current literature data and the authors' material on the interstitial lung diseases (ILD) are presented. The authors' material includes the results of morphological (light and electron microscopy) examination of 36 intrabronchial biopsies in ILD patients, 2 open biopsies, 6 autopsy cases and lungs of laboratory animals with various forms of the bronchoalveolar sclerosis and interstitial pneumonia. ILD is shown to be a chronic inflammatory lung condition with a cooperation between the immunocompetent and inflammatory cells in the alveolar septa and fibrosis of the alveolar walls. The disturbance of the immune homeostasis, particularly that of cell immunity, plays a role in the ILD pathogenesis. Complex intercellular relationships, in which the mediators of cell-to-cell interaction are of importance, are being established in the alveolar interstitium. This makes ILD morphology resembling that of the immune inflammation in other organs. So-called "neutrophilic alveolitis" induced by the immune complexes is of great importance in the pathogenesis of certain diffuse ILD forms, for example, the cryptogenic fibrosing alveolitis. The "neutrophilic alveolitis" is characterized by the presence of few neutrophils among the mononuclear cells infiltrating the alveolar septa. The alterations of the arteries, veins and capillaries in ILD may be subdivided into haemodynamic and inflammatory. ILD can be reproduced experimentally by either intravenous or intratracheal administration of antigen.