Previous studies revealed that the filaments of cytokeratin express different antigenic sites in the basal and suprabasal cell compartment of the skin and oral mucosa. It has been demonstrated that the keratin polypeptide subunit of molecular weight 67,000 dalton (67K) is a valuable marker of the suprabasal cells, since the normal basal cells remain unlabeled by antibodies against this large polypeptide. In the present study, the distribution of the 67K polypeptide has been investigated on human and guinea pig keratinocyte suspensions, purified basal cells of guinea pigs, normal human abdominal skin and normal human buccal mucosa, using the indirect immunoperoxidase method. The results of this investigation confirmed ultrastructurally that the 67K-antigen expression is lacking in the epidermal basal cell compartment. However, it could be shown that 67K polypeptide is a component of the tonofilaments in the upper Malpighian cell layers of the skin and oral mucosa. These observations suggest that keratinocyte differentiation is accompanied by modifications of antigenic determinants of the keratin filaments.
