DETECTING PROLIFERATING CELL NUCLEAR ANTIGEN IN ARCHIVAL RODENT TISSUES

The detection of proliferating cell nuclear antigen (PCNA), an endogen ous cell replication marker, has lacked sensitivity in paraffin-embedd ed archival tissues fixed in formalin. An enhanced immunohistochemical procedure to detect PCNA has been successfully applied to rat and mou se tissues. Tissue sections are heated in a microwave oven in the pres ence of an antigen-retrieval solution of heavy-metal salts. Positive i mmunostaining of S-phase cells, an indication of DNA replicative activ ity, has been consistently obtained in tissues fixed for more than 24 months in formalin and in paraffin blocks stored for up to 19 months. Use of this technique will allow retrospective staining of rodent tiss ues from previously conducted toxicity and carcinogenicity studies.