Expression of trichohyalin in dermatological disorders: a comparative study with involucrin and filaggrin by immunohistochemical staining

To investigate the function of trichohyalin during terminal differentiation of the skin, immunohistochemical studies were performed on trichohyalin an d its related proteins, filaggrin and involucrin, the components of the cor nified cell envelope, In skin disorders unrelated to tumours, weak trichohy alin expression was found in a few granular cells or in the horny layer of psoriasis, ichthyosis, keratosis pilaris, porokeratosis, chronic dermatitis and callus, Similar trichohyalin expression was found in epidermal tumours , such as seborrheic keratosis, actinic keratosis, Bowen's disease and well -differentiated squamous cell carcinoma. In follicular tumours, trichohyali n expression was positive in trichoepithelioma, keratotic basal cell epithe lioma, proliferating trichilemmal tumour, trichilemmoma, pilomatricoma and keratoacanthoma, From comparative studies with filaggrin and involucrin, tr ichohyalin expression was co-localized with them in molluscum contagiosum, keratoacanthoma and pilomatricoma. From this study, trichohyalin is reveale d to have close functional relationship with other markers of terminal diff erentiation as a precursor of the cornified cell envelope of the skin.