Effect of CAPs exposure on mucous cell metaplasia in allergic pulmonary airways. Photomicrographs of the respiratory airway epithelium lining the axial airway in lungs of rats sensitized and challenged with saline (A, B), or with Ovalbumin (C-F). Rats were exposed to filtered Air (A-D) or to CAPs in Detroit (E) or Grand Rapids (F). Tissues were stained with AB/PAS to identify intraepithelial mucosubstances (identified by arrows). al = airway lumen; ap = alveolar parenchyma; e = epithelium; int = interstitium; arrows = intraepithelial mucosubstances. Magnification bar = 50 μm.