Immunohistological detection of proliferating cells in normal and psoriatic epidermis using Ki-67 monoclonal antibody

Ki-67 monoclonal antibody (mAb) has been suggested to react only with proliferating cells. In order to study epidermal proliferating cells, immunohistological staining was performed with Ki-67 on 14 skin specimens from normal subjects and 30 from patients suffering from psoriasis. Staining of nuclei by Ki-67 was clearly observed in the epidermis. In normal epidermis, Ki-67+ cells were sparse in the basal layer (L1) and next upper layer (L2), while in psoriatic epidermis, they were abundant in L1, L2 and a few layers above L2. The percentage of positive cells in L1 of normal and psoriatic skin were 4.5 and 54%, respectively. Double staining (Ki-67 and S phase stain using bromodeoxyuridine) was also performed, and the results showed that: 1) the distribution patterns of Ki-67+ cells and those of S phase cells were similar in every section examined; 2) Ki-67 stained almost all S phase cells, and 3) Ki-67 also recognized considerable numbers of non-S phase cells. Therefore our data indicate that Ki-67 can detect a certain population of epidermal proliferating cells that includes S phase cells. Although it remains unclear whether all the proliferating cells in the epidermis can be detected by this mAb, we suggest that Ki-67 staining is an easy and useful technique for evaluating the proliferative activity of the epidermis.