PROLIFERATING CELL NUCLEAR ANTIGEN STAINING OF FISCHER-344 N RAT SPLEENS AFFECTED BY LARGE GRANULAR LYMPHOCYTE LEUKEMIA/

Large granular lymphocyte (LGL) leukemia commonly occurs in the Fische r-344/N rat, The high spontaneous incidence complicates the interpreta tion of results from chronic carcinogenicity studies that use this rat strain. As a result, a comprehensive characterization of LGL leukemia is necessary to help understand the leukemogenic process and the appl icability of staging for assessing the progression of this disease. In the current study, the proliferation rate of LGL leukemia cells from untreated control Fischer-344 (F-344) rats in 3 stages of leukemia com pared to nonleukemic age-matched rats was determined by immunohistoche mical staining for proliferating cell nuclear antigen (PCNA). In histo logic sections of spleen from aged F-344/N rats affected by LGL leukem ia, there was a significant increase of both PCNA labeling and mitotic indices that was most advanced in the spleen of rats with more severe LGL leukemia. These results support biological significance for the m orphologic staging system currently in use.