KERATINOCYTE DIFFERENTIATION IN PSORIATIC SCALP - MORPHOLOGY AND EXPRESSION OF EPITHELIAL KERATINS

The morphology of hair follicles was examined in psoriatic scalp biops ies and compared with normal scalp. In scalp psoriasis the lower outer root sheath and hair matrix were not affected by the psoriatic change s, although there was an irregular expansion in the proximal lower out er root sheath. This area has been characterized, by the presence of k eratin K19-containing cells, as the putative stem cell region. In addi tion, marked shrinkage of the sebaceous glands was seen in the psoriat ic scalp, as previously reported. A panel of monospecific monoclonal a ntibodies to individual epithelial keratins was used to analyse scalp specimens immunohistochemically. Keratin expression in scalp was gener ally unaffected by psoriasis, except for widespread expression of supr abasal keratins K16 and K17 in suprabasal interfollicular psoriatic sc alp epidermis. Simple epithelial keratins K8 and K18 were not found in follicular epithelium from either normal or psoriatic scalp, using mu ltiple monospecific antibodies. This study shows that keratin K17 is i nduced suprabasally during epidermal hyperproliferation, and cannot th erefore be considered a hair follicle-specific keratin.