Systemic and eosinophilic lesions in rats with spontaneous eosinophilia (mes rats)

The mes rat is from an inbred mutant colony of rats with spontaneous eosinophilia. In order to investigate the pathogenesis of the mes rat, the histopathology and hematology for 76 mes rats were examined at several weeks of age. Tissue eosinophilia developed at 8 weeks of age when the blood eosinophil was 500 cells per microliter or more. Subsequently, eosinophilia progressed with age, and splenic eosinophilopoiesis and erythropoiesis appeared simultaneously. Many inflammatory lesions were induced after 10 weeks of age when the blood eosinophils became 1,000 cells per microliter or more. Gastroenteritis and mesenteric lymphadenitis were seen in 44 of 47 (94%) and 31 of 47 (66%) rats, respectively, after 10 weeks of age. Aortitis that deteriorated with age was found in 19 of 39 (49%) rats after 12 weeks of age. Hepatic fibrosis was found in four rats that exhibited severe eosinophilia and anemia. These results are comparable to the features of a hypereosinophilic syndrome in humans and other animals.