[Peroxidase deficiency in eosinophils: an optical and electron microscopy cytologic study apropos of a case]

A case of eosinophil peroxidase deficiency (EPO), discovered using an automated differential leukocyte cell counter, was studied using optical and ultrastructural cytologic methods. The blood and bone marrow eosinophilic cells had an abnormal ultrastructural aspect with important modifications of the specific granule matrix. No peroxidase activity could be revealed in these cells using optical or ultrastructural techniques. The mechanism and significance of this anomaly raise the question of the physiological function of this enzyme.