Ki-67 immunostaining of normal human epidermis:: Comparison with 3H-thymidine labelling and PCNA immunostaining

Background: The size of the germinative growth fraction (i.e. the number of actively proliferating germinative cells) of normal human epidermis is still a subject of debate. Ki-67 antigen and PCNA, an auxiliary protein of delta-polymerase, are considered as markers of the growth fraction when used under optimal conditions. Method: In the present work, we have compared Ki-67 expression (detected with MIB 1 antibody) with PCNA expression (detected with PC10 antibody) in biopsies of normal human epidermis fixed in neutral formalin and using antigen retrieval by microwave processing. To obtain additional information, such as the percentage of cells in S phase, biopsies were also incubated in H-3-thymidine before immunostaining. Results: Before microwave treatment, 8% of the basal cells were positive for MIBI antibody and 7.8% were positive for PC10 antibody. The H-3-thymidine labelling index was 2.8%. The proportion of MIB1-positive cells rose to 19% after antigen retrieval by microwave processing. In the same way, the H-3 labelling index rose to 9%. In contrast, PC10 became positive in all epidermal nuclei. Conclusion: These results suggest that the growth fraction of the germinative cell population of normal human epidermis is not larger than 20% and is composed of cells with a short cell cycle time.