The origin, nature, and distribution of polymorphonuclear leukocyte (PMN) granules were invcstigated by examining developing granulocytcs from normal rabbit bone marrow which had been fixed in glutaraldchyde and postfixed in OsO4. Two distinct types of granules, azurophil and specific, were distinguished on the basis of their differences in size, density, and time and modc of origin. Both types are produced by the Golgi complex, but they are formed at diffcrcnt stages of maturation and originate from different faces of the Golgi complex. Azurophil granules arc larger (~800 m/z) and more dense. ~[hcy arc formed only during the progranulocyte stagc and arise from the proximal or concave face of thc Golgi complex by budding and subsequent aggregation of vacuoles with a dcnse core. Smaller (~500 m/z), less dense specific granules arc formed during the myclocytc stage; they arise from the distal or convex face of the Golgi complex by pinching-off and confluence of vcsiclcs which have a finely granular content. Only azurophil granules are found in progranulocytes, but in maturc PMN relatively few (10 to 20%) azurophils are seen and most (80 to 90%) of the granulcs present are of the specific type. ~[he results indicate that invcrsion of the azurophil/specific granule ratio occurs during the myelocyte stage and is due to: (a) reduction of azurophil granules by multiple mitoses; (b) lack of new azurophil granule formation after the progranulocyte stage; and (c) continuing specific granule production. The findings demonstrate thc existence of ~wo distinct granule types in normal rabbit PMN and their separate origins from the Golgi complex. The implications of the observations are discussed in relationship to previous morphological and cytochemical studies on PMN granules and to such questions as the source of primary lysosomcs and thc concept of polarity within the Golgi complex. Downloaded from jcb.rupress.org on February 21, 201
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