Alveolar macrophage lysosomal enzyme and C3b receptors in cryptogenic fibrosing alveolitis.

Levels of the lysosomal enzyme N-acetyl-beta-glucosaminidase were measured in alveolar macrophage extracts and lung lavage fluid obtained from patients with cryptogenic fibrosing alveolitis and a control group. Evidence is presented which suggests that macrophages from patients with cryptogenic fibrosing alveolitis secrete this enzyme in vivo. To investigate one of the possible mechanisms of stimulating this secretion, an assessment was made of the C3b receptor sites on alveolar macrophages. While there were fewer receptor sites on the macrophages from patients with cryptogenic fibrosing alveolitis, which might indicate that they were occupied in vivo, this difference did not reach statistical significance. It is suggested that the alveolar macrophage is not merely a phagocyte but that it also has a more active role in the pathogenesis of cryptogenic fibrosing alveolitis.