Keratin 7 staining in squamous metaplasia of the epithelium of a bronchiolus (human, adult)

Stain: anti-keratin 7 antibody (Pan-Ck 7) immunoperoxidase staining (with aminoethylcarbazole (AEC) substrate). A red-brown staining with AEC indicates a positive reaction for cytokeratin 7. Note that the top layer only is stained positively for keratin 7 (↓). Upon squamous metaplasia the bronchiolar epithelial cells reduce keratin 7 expression and hence this cytokeratin appears a suitable marker in the study of early metaplastic processes in epithelia e.g., the bronchial tree