Ultrastructural Immunolocalization of Involucrin in the Medulla and Inner Root Sheath of Human Hair

The study investigated the role of involucrin in the cornification of human hair using light and electron microscopy immunohistochemistry. It found that involucrin was absent in keratinized cuticle and cortical cells but present in the cytoplasm of keratinizing cells in the medulla and inner root sheath. During cell maturation and cornification, involucrin concentrated in the peripheral cytoplasm and along the plasma membrane, similar to epidermal corneocytes. This suggested that involucrin, along with trichohyalin, contributed to the formation and mechanical resistance of the corneous material in the medulla and inner root sheath by forming isopeptide bonds.