Quantitative histological changes produced in the tracheal mucosa of young chickens by the inhalation of sulfur dioxide in low concentrations

Chickens were exposed to SO₂ in relatively low concentrations (3.4 to 18.5 parts per million (ppm)) for 1 to 14 days. A portion of their tracheas was embedded in water-soluble methacrylate, cut at 2 μm and stained with hematoxylin and eosin, Wright's stain, methyl green-pyronin, Alcian blue - periodic acid Schiff, and for acid phosphatase. An increase was found in (a) the mucosa to wall ratio; (b) the number of mucosal cells in mitosis; (c) the number of macrophages, lymphocytes, plasma cells, and neutrophils in the epithelium and lamina propria; and (d) the number of these infiltrating cells which contained acid phosphatase. The number of mucus- and seromucus-secreting cells and vasoamine-containing cells were sometimes increased, but not consistently. The percentage of cells containing sialidase-sensitive sialomucins was elevated, and the percentage of cells containing neutral mucins was reduced. These changes were only partly related to the SO₂ concentration and the duration of SO₂ exposure, in that increasing amounts of SO₂ did not always cause increasing changes in the mucin composition. Evidently, the altered mucins sometimes protected against further mucin modification.