Automatic classification of cells in cell cycle phases based on Ki-67 antigen quantification by fluorescence microscopy.
Ki-67 antigen is thought to be a marker of cell proliferation, as it can be detected in cycling cells, i.e. cells in G1, S, G2 and M phases, but not in resting cells. The immunocytochemical staining pattern obtained by the Ki-67 monoclonal antibody varies, depending on the cell cycle phases. Analysis of double staining of Ki-67 antigen and DNA in the MCF-7 cell line by videomicrofluorometry allows the description of both the level and the pattern of Ki-67 staining in the form of a set of parameters defining each cell. These parameters were measured in MCF-7 cell populations characterized according to their position in the cell cycle. They were submitted to a statistical analysis (principal component and discriminant analysis) which allowed the determination of the optimal parameters to characterize a given cellular group and permitted the use of these parameters for an automatic classification of cells in the different cell cycle phases. In G1, S, G2, prophase + metaphase and anaphase + telophase cells, these parameters allowed a classification of cells with a good-classification rate of 94.37%. A comparison of this method with methods based on the DNA histogram and bromodeoxyuridine uptake was performed. The classification coefficients stemming from the discriminant analysis were introduced into a program to obtain, automatically, the Ki-67 labelling index and the percentages of cells in each phase. This method, which allows a quick evaluation of the proliferation and the phase indices, may be more widely applicable.