Keratinocytes express dipeptidyl-peptidase IV (CD26) in benign and malignant skin diseases

CD26 expression on keratinocytes, in both normal and pathological skin, was investigated using immunohistochemical techniques. A sporadic focal CD26 positivity was found in normal skin, whereas increased expression of CD26 was observed both in cutaneous T-cell lymphomas and in inflammatory skin diseases, e.g. psoriasis, lichen planus and spongiotic dermatitis, in the basal and spinous layers. CD26 keratinocyte staining was not specific for a single disease, but seems to be associated with the presence of a reactive or neoplastic infiltrate in the epidermis. We propose that the CD26 molecule may function as a keratinocyte activation antigen.