Cell kinetic analysis of brain tumors using the monoclonal antibody Ki-67: in vitro and in situ study.

Ki-67 is a commercially available mouse monoclonal antibody (MoAb), which reacts with a nucleolar antigen (the Ki-67 antigen) expressed in proliferating eukaryotic cells. The author examined the precise localization of the Ki-67 antigen in C-6 cells using immunohistochemical and immunoelectron microscopic methods and estimated the proliferative activity of human brain tumors in situ. Positive nucleoplasmic reactions (early G1 phase) and nucleolar staining (late G1 phase) were observed. The cells showed very weak positive reactions in only one or two nucleoli (S phase) and multiple spicule reactions in the nucleoplasm (G2 phase). During the mitotic phase, the Ki-67 antigen was stained on the surfaces of all chromosomes and finely dispersed in the cytoplasm. By immunoelectron microscopic study, positive reactions were observed on the granular and dense fibrillar components. Therefore, the Ki-67 antigen seems to participate in the processing and assembly of preribosomal particles. In human brain tumors, the Ki-67 score (positive cells/total neoplastic cells), ranging 0 to 36.7%, correlated well with the histopathological grade of malignancy of the tumor. These findings suggest that immunohistochemical staining with the MoAb Ki-67 can be used as a convenient procedure for the simple evaluation of the proliferative activity of brain tumors.