Hematological characteristics of rats spontaneously developing eosinophilia.

Hematological and genetic characteristics of newly found eosinophilic rats were studied. Hematologically, high blood eosinophil counts started at 6 weeks of age. Almost all 10-week-old rats had eosinophilia with individual counts above 500/microliter and 5 to 100 times the normal level. Proliferating eosinophils had normal morphology. An increase in lymphocyte counts was observed at 5 weeks of age, one week earlier than the onset of eosinophilosis. In bone marrow, proliferation of eosinophils was also observed at 8 weeks of age and thereafter progressed, suggesting a role in the pathogenesis of eosinophilia in this rat. The results of genetic cross experiments revealed the disease to be hereditary. The spontaneously eosinophilic rat therefore warrants attention as a model for studying the underlying mechanisms of human and animal eosinophilia.