BN.MES-Cybames Congenic Rats Manifest Focal Necrosis with Eosinophilic Infiltration in the Liver without Blood Eosinophilia

The Matsumoto Eosinophilia Shinshu (MES) rat strain develops hereditary blood eosinophilia and eosinophil-related inflammatory lesions in organs due to the mutant Cybames gene. We hypothesized that a new eosinophilia model with a different phenotype could be established by changing the genetic background of rats. We bred and characterized a congenic strain, in which the mutant Cybames gene was introduced into the background of a BN strain (BN.MES-Cybames). The congenic rats showed robust proliferation of eosinophils in the bone marrow. Nonetheless, blood eosinophil levels of the rats remained within the normal range. In addition, the rats manifested focal necrosis with eosinophilic infiltration in the liver, a phenotype rarely observed in the original MES rat strain. These results imply the presence of genetic polymorphisms between MES and BN strains which modulate the mobilization of eosinophils to the peripheral circulation and organs. The newly established BN.MES-Cybames congenic rat strain, together with the original MES strain, will provide useful models for elucidating the molecular genetic mechanisms involved in the development and trafficking of eosinophils.