Eosinophil peroxidase deficiency in New Zealand white mice

Eosinophil peroxidase (EPO) is one of the granule enzymes in the eosinophil-specific granules and is distinct from myeloperoxidase. Here we report that peroxidase activity was absent in eosinophils of New Zealand White (NZW) mice. When NZW, New Zealand Black and their F1 mice were treated with cyclophosphamide followed by Toxocara canis infection, the kinetic changes in the number of eosinophils in peripheral blood, determined by counting in Hinkelman's diluting fluid, were almost comparable among the three strains. However, when their blood films were stained for peroxidase reaction, eosinophils of NZW mice, but not of the other strains, lacked EPO activity, though their specific granules were stained by eosin Y. Sudan black staining for phospholipid was also negative in eosinophils of NZW mice. EPO deficiency in NZW eosinophils was further confirmed by electron-microscopic observations and by measuring EPO activity in the extracts of eosinophil-rich cell suspensions. These results indicate that NZW eosinophils share most of the features with human EPO-deficient eosinophils, suggesting that the NZW mouse is a murine counterpart of human EPO deficiency.