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Origin of granules in polymorphonuclear leukocytes. Two types derived from opposite faces of the Golgi complex in
Abstract:
The origin, nature, and distribution of polymorphonuclear leukocyte (PMN) granules were investigated by examining developing granulocytes from normal rabbit bone marrow which had been fixed in glutaraldehyde and postfixed in OsO(4). Two distinct types of granules, azurophil and specific, were distinguished on the basis of their differences in size, density, and time and mode of origin. Both types are produced by the Golgi complex, but they are formed at different stages of maturation and originate from different faces of the Golgi complex. Azurophil granules are larger ( approximately 800 mmicro) and more dense. They are formed only during the progranulocyte stage and arise from the proximal or concave face of the Golgi complex by budding and subsequent aggregation of vacuoles with a dense core. Smaller ( approximately 500 mmicro), less dense specific granules are formed during the myelocyte stage; they arise from the distal or convex face of the Golgi complex by pinching-off and confluence of vesicles which have a finely granular content. Only azurophil granules are found in progranulocytes, but in mature PMN relatively few (10 to 20%) azurophils are seen and most (80 to 90%) of the granules present are of the specific type. The results indicate that inversion 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 the existence of two 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 lysosomes and the concept of polarity within the Golgi complex.
Insights
Polymorphonuclear leukocyte (PMN) granules originate from the Golgi complex. Two distinct types, azurophil and specific, form at different maturation stages, leading to a ratio inversion in mature PMNs.
Area of Science:
- Cell Biology
- Hematology
- Granulopoiesis
Background:
- Polymorphonuclear leukocytes (PMNs) contain granules crucial for their function.
- The origin and differentiation of these granules are not fully understood.
Purpose of the Study:
- To investigate the origin, nature, and distribution of PMN granules.
- To distinguish between azurophil and specific granule types.
Main Methods:
- Examination of developing granulocytes from rabbit bone marrow.
- Glutaraldehyde and OsO(4) fixation for electron microscopy.
Main Results:
- Two distinct granule types identified: azurophil (larger, denser) and specific (smaller, less dense).
- Both granule types originate from the Golgi complex but at different maturation stages and faces.
- Azurophil granules form in progranulocytes; specific granules form in myelocytes.
- Ratio of azurophil to specific granules inverts during myelocyte stage due to reduced azurophil production and continued specific granule production.
Conclusions:
- Confirms two distinct PMN granule types with separate Golgi origins.
- Explains the granule ratio inversion during PMN maturation.
- Provides insights into primary lysosome sources and Golgi complex polarity.