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 epitheloid mesothelioma from non-epitheliod mesothelioma and adenocarcinoma. It is also a useful antibody to distinguish benign ductal hyperplasias from non-invasive neoplastic proliferations. Positive tissue: Skin.