A new way to evaluate the germinative compartment in human epidermis, using [3H]thymidine incorporation and immunoperoxidase staining of 67 K polypeptide

We have used tritiated thymidine (3HT) labelling and immunoperoxidase staining of 67 K polypeptide in human epidermis to study normal skin before and after irritation induced by application of croton oil (20% and 50% in olive oil). By this double labelling method, it was possible to identify, on the same skin section, DNA-synthesizing nuclei and epidermal cells which contained 67 K polypeptide. Our results clearly indicate that the germinative compartment of normal epidermis is a mixed population comprising basal and adjacent suprabasal cells; as a rule, absence of expression of 67 K polypeptide, which characterizes all basal cells, could not be regarded as a good marker to distinguish the germinative from the differentiating compartments. In mild primary irritation, the ratio of 3HT-labelled undifferentiated cells to keratinizing ones was similar to that observed in normal epidermis. In severe irritation, this homeostatic process was altered, as 3HT-labelled cells were mainly 67 K negative.