KI-67 (MIB-5) IMMUNOSTAINING OF MOUSE LUNG-TUMORS INDUCED BY 4-NITROQUINOLINE 1-OXIDE

We immunostained mouse lung tumors using a mouse monoclonal antibody a gainst recombinant Ki-67 antigen (clone; MIB 5) to establish an MIB 5 immunostaining method and to determine the extent of MIB 5 labeling to monitor cell proliferation activity in mouse lung tumors. A/J mice, t reated with 4-nitroquinoline 1-oxide, were killed after 18 months. One hour before killing, bromodeoxyuridine (BrdU) was injected intraperit oneally. Lung tissues including tumors were fixed with phosphate-buffe red 4% paraformaldehyde and embedded in paraffin. For MIB 5 immunostai ning, two antigen-retrieval buffers, citrate buffer pH 6 and TRIS-HCl buffer pH 9.5 containing 5% urea, were tested, and constant and reprod ucible staining was obtained only with the TRIS-HCl buffer. The mean v alues of the MIB 5-positive cell index (PCI), the BrdU labeling index (LI), and the mitotic cell count for adenocarcinomas were 4.6%, 2.3%, and 7/mm(2), and those for adenomas were 1.2%, 0.7%, and 1.3/mm(2), re spectively. Each of these values was significantly higher for adenocar cinomas than for adenomas. A close correlation was seen between the MI B 5 PCI and the BrdU LI for adenocarcinomas and adenomas and between t he MIB 5 PCI and the mitotic cell count in adenocarcinomas. Thus, MIB 5 immunostaining is a useful method for assessing the proliferative ac tivity of mouse tumor tissues.