Effect of sulphur dioxide on the enzyme activity of the alveolar macrophage of rats.

Adult rats were exposed to sulphur dioxide to induce hypersecretion of mucus and so increase the amount of mucus reaching the alveoli. The comparative activity of four lysosomal hydrolytic enzymes was studied histochemically in free alveolar cells, thought to be macrophages, from the lungs of the exposed and control animals. Although the activity of β-glucuronidase, β-galactosidase, and N-acetyl-β-glucosaminidase appeared increased in some free alveolar cells in the peribronchiolar region, a marked increase of acid phosphatase activity was seen in the free alveolar cells throughout the lung parenchyma. It is suggested that in rats acid phosphatase in alveolar macrophages is connected with the catabolism and removal of mucopolysaccharide and increases in response to the extra amount of mucus reaching the alveoli after respiratory irritation with sulphur dioxide.