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eratins are a large family of proteins that form the intermediate filament cytoskeleton of epithelial cells, which are classified into two major sequence types. Type I keratins are a group of acidic intermediate filament proteins, including K9–K23, and the hair keratins Ha1–Ha8. Type II keratins are the basic or neutral courterparts to the acidic type I keratins, including K1–K8, and the hair keratins, Hb1–Hb6. Keratin 14 is a type I cytokeratin. It is usually found as a heterotetramer with keratin 5. Keratins K14 and K5 have long been considered to be biochemical markers of the stratified squamous epithelia, including epidermis.