Partial myeloperoxidase deficiency in a case of preleukaemia. I. Studies of fine structure and peroxidase synthesis of promyelocytes.

Summary. The ultrastructural localization of peroxidase activity has been studied in the circulating neutrophils and in a neutrophilic series of bone marrow cells from a patient with preleukaemia. Light microscopic examination showed 36% of the polymorphonuclear leucocytes to be totally devoid of myeloperoxidase, while 50% were normally stained and 14% were slightly positive for this enzyme. Electron microscopic studies revealed considerable heterogeneity in the promye-locyte population, since the number of peroxidase-deficient azurophil granules was seen to vary from o to 100% in these cells. Thus, several types of promyelocytes were identified. One cell type, which resembled that seen in normal subjects, contained myeloperoxidase within its azurophil granules and also within the cisternae of the rough endoplasmic reticulum and Golgi complex. A second type of pro-myelocyte, which was at an early stage of development, lacked myeloperoxidase in its secretory apparatus. These cells contained two species of azurophil granules, the first of which was devoid of peroxidase activity whereas the other reacted positively. These observations suggest that the premature arrest of myeloperoxidase synthesis in the promyelocytes from a preleukaemic patient may give rise to several populations of circulating neutrophils which can exhibit varying contents of myeloperoxidase.