Related Experiment Videos
The development of neutrophilic polymorphonuclear leukocytes in human bone marrow
Abstract:
Neutrophilic leukocytes (PMN) and their precursors from normal human marrow and blood were examined by histochemical staining and by electron microscopy and cytochemistry in order to determine the origin and nature of their cytoplasmic granules. Human neutrophils contain two basic types of granules, azurophils and specifics, which differ in morphology, contents, and time of origin. Azurophils are large and may be spherical or ellipsoid, the latter with a crystalline inclusion. They are produced in the first secretory stage (promyelocyte), contain peroxidase and various lysosomal enzymes, and thus correspond to modified primary lysosomes. Specifics are smaller, may be spherical or elongated, and are formed during a later secretory stage (myelocyte). They lack lysosomal enzymes and contain alkaline phosphatase and basic protein; their contents remain largely undetermined. Specifics outnumber azurophils in the mature PMN because of reduction in numbers of azurophils per cell by cell division in the myelocyte stage. The findings indicate that the situation is basically the same as described previously in the rabbit, insofar as the origin, enzymic activity, and persistence in the mature cell of the two types (azurophil and specific) of granules are concerned. The main difference between PMN of the two species is in the morphology (size, shape, and density) of the granules, especially the azurophils.
Insights
Human neutrophils contain two granule types: azurophils and specifics. Azurophils form early, containing lysosomal enzymes, while specifics form later with undetermined contents, differing morphologically from azurophils.
Area of Science:
- Hematology
- Cell Biology
- Immunology
Background:
- Neutrophilic leukocytes, or polymorphonuclear neutrophils (PMN), play a critical role in innate immunity.
- The cytoplasmic granules within PMNs are essential for their microbicidal and inflammatory functions.
- Understanding the origin and composition of these granules is key to comprehending PMN biology.
Purpose of the Study:
- To investigate the origin and characteristics of cytoplasmic granules in human neutrophils.
- To differentiate between the two main types of granules: azurophils and specifics.
- To compare human neutrophil granules with those of rabbit neutrophils.
Main Methods:
- Histochemical staining of human marrow and blood cells.
- Electron microscopy and cytochemistry.
- Analysis of granule morphology, content, and origin during neutrophil maturation.
Main Results:
- Human neutrophils possess two distinct granule types: azurophils and specifics, differing in size, shape, content, and origin.
- Azurophils, formed in promyelocytes, contain peroxidase and lysosomal enzymes, resembling modified lysosomes.
- Specifics, formed in myelocytes, lack lysosomal enzymes but contain alkaline phosphatase and basic proteins; their contents are largely unknown.
Conclusions:
- Azurophil and specific granules originate at different stages of neutrophil development and have distinct compositions.
- Specific granules become more numerous than azurophils in mature neutrophils due to cell division.
- Human and rabbit neutrophils share fundamental granule characteristics, with notable species-specific morphological differences, particularly in azurophils.