A panel of antibodies for identifying squamous metaplasia in endobronchial biopsies from smokers

Toxic injury can induce squamous metaplasia of respiratory epithelium, which normally is pseudostratified. Terminally differentiated squamous epithelial cells have a flattened, elongated appearance. During differentiation, they have an intermediate phenotype that is difficult to identify and distinguish from tangentially cut columnar cells in tissue sections from endobronchial biopsies, whose small size makes orientation difficult. The aim of our study was to develop a panel of antibodies that could be employed to distinguish normal epithelium from metaplastic epithelium and would be suitable for use on endobronchial biopsies. Nasal polyp tissue and tonsil tissue, which have pseudostratified and squamous epithelia, respectively, were collected from surgical cases and embedded in glycol methacrylate resin. Cut sections were stained immunohistochemically with a panel of antibodies to cytokeratins (CK), whose expression varies with epithelial type and stage of differentiation, and involucrin, a marker of terminal squamous differentiation. Squamous epithelium stained positively for CK5/6, CK13 and involucrin. In the pseudostratified epithelium, basal cells exhibited weak staining for CK13 and strong staining for CK5/6, and columnar cells exhibited strong immunoreactivity for CK7, CK8 and CK18. Application of this panel to endobronchial biopsies from smokers enabled areas of squamous metaplasia to be distinguished from tangentially sectioned epithelium.