This antibody specifically targets keratin K1 in the upper layers of cornified squamous epithelia, such as the scalp and foot sole. It does not react with non-keratinizing stratified or non-stratified epithelia, like those found in the esophagus or duodenum. The polypeptide it reacts with is basic human keratin K1, with a molecular weight of 66,000. A positive control is human foot sole.