Anisocytosis precedes onset of the large granular lymphocyte leukemia in aged F344/N rats

In investigations using experimental animals, the unexpected affection of certain diseases often cause great impairment to them especially when using aged animals. In F344 rats, large granular lymphocyte leukemia is the most frequent fatal disease which increases along their aging. The timely detection of rats at risk for leukemia is very important in order to exclude such animals and thus obtain precise results in many fields of investigation. In the process of assessing the main cause of death in F344/N rats of the aging farm of our institute, NILS, we found cases with no obvious contributory disease to death that showed anisocytosis in a peripheral blood smear. In such cases, histological examination of spleen revealed consistent features of leukemia and findings of the liver and kidney were considered due to this hematologic disorder. Anisocytosis was frequently seen in the advances stage of leukemia. Thus we concluded that anisocytosis is a prior condition of leukemia and its detection in a peripheral blood smear is predictive of the disease when using aged animals.