Keratin expression in the normal nail unit: markers of regional differentiation

The study examined keratin expression in the nail unit using antikeratin monoclonal antibodies, revealing distinct patterns of differentiation. The nail matrix uniquely expressed the acidic hair-type keratin Ha1, alongside epidermal keratins K1 and K10, with occasional K17 at the matrix apex. K6 and K16 were present at the ventral aspect of the proximal nail fold. The nail bed lacked Ha1 and markers of cornified and mucosal differentiation but contained K6, K16, and K17, indicating minimal differentiation due to the nail's properties. In the digit pulp, K6, K16, and K17 were found in limited amounts, possibly linked to the eccrine duct's epidermal component. Simple epithelial keratins K7, K8, and K18 were present in younger individuals, mainly in epibasal cells and putative Merkel cells.