NUCLEAR ANTIGEN EXPRESSED BY PROLIFERATING CELLS

We describe a novel mouse monoclonal antibody (PRA-72) that recognizes a nuclear antigen associated with cell proliferation. The monoclonal antibody stained the nuclei of logarithmically growing cultured stroma l cells. The nuclear staining disappeared when these cells entered G(0 ) phase of the cell cycle. Western blot analysis revealed a nuclear pr otein which appeared as a doublet at 35-40 KD, which was undetectable in extracts from confluent cells. Immunocytological study of purified cell populations from various cell cycle phases revealed peripheral nu clear staining in all stages except mitosis, when the chromosomes were observed enveloped with the antigen. In co-cultures of quiescent stro mal cells and proliferating hemopoietic precursors, only the latter sh owed nuclear staining by PRA-72 monoclonal antibody. Further indicatio ns for selective expression of the antigen by proliferating cells were found by an immunohistochemical study of various tissues including ne wborn mouse bone marrow and its surrounding connective tissue, mouse t ongue epithelium, and human carcinoma of the colon. This antibody may, therefore, prove useful in the evaluation of human tumors.