USE OF IN-SITU DETECTION OF HISTONE MESSENGER-RNA IN THE ASSESSMENT OF EPIDERMAL PROLIFERATION - COMPARISON WITH THE KI67 ANTIGEN AND BRDU INCORPORATION

The labelling index is commonly used as a measure of proliferation. Ho wever, the use of tritiated thymidine or BrdU labelling of S-phase cel ls is limited to prospective samples. We have employed an oligonucleot ide cocktail complementary to the mRNA species encoding the replicatio n-dependent histones H2B, H3 and H4 for non-isotopic in situ hybridiza tion (NISH), and have compared the resultant proliferation indices in normal skin with those obtained by bromodeoxyuridine (BrdU) incorporat ion and by Ki67 immunohistochemistry (IHC) using the monoclonal antibo dy MIB1. In addition, we compared the staining characteristics of hist one NISH and Ki67 MC in a further 25 samples from a variety of inflamm atory dermatoses and neoplastic conditions, as well as from normal ski n. In normal skin, S-phase (histone NISH and BrdU) and cycling (Ki67) cells were confined to the basal and low suprabasal layers. The labell ing indices determined by histone NISH and BrdU incorporation were sim ilar, whereas that of Ki67 IHC was four times greater. In biopsies fro m hyperproliferative dermatoses and dysplastic or malignant lesions, t he number of histone NISH- and Ki67 IHC-positive cells was generally e levated; in accordance with the differential expression of these two m arkers during the cell cycle, MIB1 consistently gave higher results. T he advantage of histone NISH over Ki67 IHC is that it is a marker of t he same part of the cell cycle as BrdU incorporation. However, the com bined use of both histone NISH and Ki67 IHC to measure two cell cycle parameters, namely S-phase and the number of cycling cells, allows mor e detailed retrospective study of epidermal proliferation than has bee n possible previously.