Mitotic and Labelling Activity In Normal Human Epidermis In Vivo

Abstract

Labeling and mitotic indices were studied in the epidermis of 28 young men. A mean labeling index of 5.5% was found from the whole study and a mean mitotic index of 0.06%. Mitotic index particularly was extremely variable; indices between 0.002-0.438% were found in individual biopsies. In the 1st 2 of 3 experiments in which mitotic index at 09.00 h was compared with that at 15.00 h, significant differences were found (15.00 h > 09.00 h by a factor of 2.6, P < 0.001). In the 3rd such experiment, no such difference was found, suggesting that the timing and occurrence of diurnal rhythms of mitotic activity may not be consistent in normal human epidermis. In the 1 experiment in which it was investigated, a significantly higher mitotic index was found at 21.00 h compared to 09.00 and 15.00 h. Labeling index did not vary significantly at 09.00, 15.00 or 21.00 h. Labeling index did show a significant pattern of change over a 12-mo. period in 2 groups of subjects; peaks of labeling were seen in July and troughs in Jan. Very high ratios of labeled:mitotic cells were found, the median ratio for the whole study being 98 labeled: 1 mitotic cell. This finding supports the possibility that not all labeled cells subsequently go on to divide in normal human epidermis.