Ki-67 Immunostaining of Normal Human Epidermis: Comparison with 3H-Thymidine Labelling and PCNA Immunostaining

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Abstract
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 d-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 MIB1 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 3H-thymidine before immunostaining. Results: Before microwave treatment, 8% of the basal cells were positive for MIB1 antibody and 7.8% were positive for PC10 antibody. The 3H-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 3H 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.

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