IMMUNOHISTOCHEMICAL EXPRESSION OF KERATIN PROTEINS IN KERATOACANTHOMAS OF THE SKIN

Keratin expression in eight cases of keratoacanthoma was examined immu nohistochemically using a panel of seven monoclonal antibodies to eith er single or a few subsets of keratin polypeptides, and compared with normal surrounding skin to evaluate their cell phenotypes. Six cases o f squamous cell carcinoma of the skin were also examined. In outer roo t sheath cells of normal hair follicles, all the cells were immunoposi tive with E3, CK8.12 and 312C8-1 antibodies, limited reactivity was se en at the level of sebaceous duct insertion with 34 beta B4, and restr icted expression was seen at the early anagen stage with KS-1A3, while all cells were totally immunonegative with RPN1165 and CK4.62. In all eight keratoacanthomas studied, 312C8-1 immunorectivity was seen in p eripheral basaloid cells of the endophytic lobules, E3, CK8.12 and 34 beta 4 immunoreactivity was found in centrally located cells with glas sy appearance, while RPN1165 and CK4.62 gave no immunoreaction. In one case, glassy type cells were positive with KS-1A3. These results sugg est that keratin expression in keratoacanthomas resembles that in the upper part of the outer root sheath cells of the hair follicle, and su ggest the possible origin of keratoacanthoma cells from those of the o uter root sheath. However, similar keratin expression was found in squ amous cell carcinomas of the skin and we were unable to distinguish th ese two conditions from their keratin reactivity.