It recognizes polypeptides of 58kDa and 56kDa, identified as cytokeratin 5 and 6 respectively. It shows no reaction with keratin 1, 8, or 19. It stains the basal cells of squamous and glandular epithelia, part of stratum spinosum of squamous epithelium, myoepithelium, and mesothelium. It does not stain adenous epithelium. Therefore, this antibody can be used to distinguish squamous carcinoma from adenocarcinoma, and to differentiate epitheliod mesothelioma from non-epitheliod mesothelioma and adenocarcinoma. It is also a useful antibody in the identification of mesothelioma and lung squamous cell carcinoma.