Quantification and topographical description of Ki-67 antibody labelling during the cell cycle of normal fibroblastic (MRC-5) and mammary tumour cell lines (MCF-7).

The expression of a human nuclear antigen associated with cell proliferation and recognized by monoclonal antibody Ki-67 was investigated during the cell cycle in a breast cancer cell line (MCF-7) and in a normal human fibroblastic cell line (MRC-5). Image cytometry was used to determine Ki-67 antigen and DNA amounts at the cell level. Results confirm Ki-67 antibody specificity for proliferating cells. The antigen expression increases with cell progression through the cycle. Image cytometry also permits the description of the Ki-67 topographic distribution at the various phases of the cell cycle. Ki-67 antigen is essentially localized in the nucleoli at G1 phase. A nucleoplasmic distribution appears later in the cell cycle. The parameters measured on the labelling allow the calculation of the growth fraction and an evaluation of the phase fractions. Other results in this study strongly suggest that nucleolar rRNA synthesis is required for Ki-67 antigen expression. Hypotheses on Ki-67 functions are proposed.