Related Experiment Videos
Sequential degranulation of the two types of polymorphonuclear leukocyte granules during phagocytosis of
Abstract:
The sequential discharge of neutrophilic polymorphonuclear leukocyte (PMN) granules-azurophils and specifics-was investigated by electron microscopy and cytochemistry. Thus the enzyme content of PMN phagocytic vacuoles was determined at brief intervals after phagocytosis of bacteria, utilizing peroxidase as a marker enzyme for azurophil granules, and alkaline phosphatase for specifics. At 30 s, approximately half the phagocytic vacuoles were reactive for alkaline phosphatase, whereas none contained peroxidase. Peroxidase-containing vacuoles were rarely seen at 1 min, but by 3 min, vacuoles containing both enzymes were consistently present. Alkaline phosphatase was found in both small and large vacuoles, whereas peroxidase was visible only in large ones. By 10 min, very big phagocytic vacuoles containing considerable amounts of reaction product for both enzymes were evident. These observations indicate that the two types of PMN granules discharge in a sequential manner, specific granules fusing with the vacuole before azurophils. In an earlier paper, we reported that the pH of phagocytic vacuoles drops to 6.5 within 3 min and to approximately 4 within 7-15 min. Substances known to be present in specific granules (alkaline phosphatase, lysozyme, and lactoferrin) function best at neutral or alkaline pH, whereas most of those contained in azurophil granules (i.e., peroxidase and the lysosomal enzymes) have pH optima in the acid range. Hence the sequence of granule discharge roughly parallels the change in pH, thereby providing optimal conditions for coordinated activity of granule contents.
Insights
Neutrophilic polymorphonuclear leukocyte (PMN) granules, specifically azurophils and specifics, are released sequentially. This ordered release of PMN granules optimizes their antimicrobial functions during phagocytosis.
Area of Science:
- Immunology
- Cell Biology
- Microbiology
Background:
- Neutrophilic polymorphonuclear leukocytes (PMNs) are crucial immune cells.
- PMNs contain distinct granule types (azurophils and specifics) with different enzyme compositions.
- The precise timing and order of granule release during phagocytosis are not fully understood.
Purpose of the Study:
- To investigate the sequential discharge of azurophil and specific granules from PMNs.
- To correlate granule release timing with the changing pH environment within phagocytic vacuoles.
- To understand how granule release order optimizes the antimicrobial activity of their contents.
Main Methods:
- Electron microscopy and cytochemistry were used to visualize granule contents.
- Peroxidase served as a marker for azurophil granules.
- Alkaline phosphatase was used as a marker for specific granules.
Main Results:
- Specific granules (alkaline phosphatase) were detected in phagocytic vacuoles earlier (30s) than azurophil granules (peroxidase, ~3 min).
- Peroxidase was found only in large vacuoles, while alkaline phosphatase appeared in both small and large ones.
- By 10 minutes, large vacuoles contained significant amounts of both enzyme markers.
Conclusions:
- PMN specific granules fuse with phagocytic vacuoles before azurophil granules.
- The sequential release of granules aligns with the decreasing pH within phagocytic vacuoles.
- This ordered discharge ensures optimal activity of granule-associated enzymes at different pH levels, enhancing bacterial killing.