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Migration of polymorphonuclear leukocytes through human amnion membrane--a scanning electron microscopic study
1Department of Biochemistry, University of Bielefeld, Faculty of Chemistry, F.R.G.
Abstract:
Scanning electron microscopy has been used to examine the changes in the basement membrane structure induced by polymorphonuclear leukocytes during leukodiapedesis. A diapedesis model based on a Boyden chamber fitted with a human amnion membrane simulated inflammatory processes during which leukocytes are stimulated to leave blood vessels and to penetrate basement membranes. In the Boyden chamber, a chemotactic gradient was developed from a solution of 10(-7) M formyl-methionyl-leucyl-phenylalanine, which induced the cells to migrate through the membrane. Our observations suggest that leukocytes, like tumor cells, emigrate in a three-step process. In the first instance, they adhere to the basement membrane. A local partial proteolysis follows, which is caused by secreted metalloproteinases, especially by gelatinase. The partial dissolution of the matrix facilitates cell penetration. Active locomotion and squeezing through the residual membrane matrix allows the cells to penetrate without complete local membrane destruction. The last step involves migration of the cells through the connective tissue barrier to the site of infection. The type I collagen fibres which form this loose stroma tissue are no obstacle and can be pushed aside without proteolytic degradation.
Insights
Polymorphonuclear leukocytes degrade basement membranes via metalloproteinases during diapedesis. This process involves adhesion, proteolysis, and migration, enabling cells to reach infection sites without destroying the membrane.
Area of Science:
- Cell Biology
- Biochemistry
- Immunology
Background:
- Leukocyte extravasation is crucial for immune response.
- Basement membrane penetration by leukocytes is not fully understood.
Purpose of the Study:
- To investigate the mechanism of basement membrane penetration by polymorphonuclear leukocytes during diapedesis.
- To elucidate the role of proteolysis in leukocyte migration through basement membranes.
Main Methods:
- Scanning electron microscopy was used to visualize basement membrane changes.
- A Boyden chamber model with human amnion membrane simulated inflammatory conditions.
- Chemotactic gradient induced leukocyte migration.
Main Results:
- Leukocytes adhere to the basement membrane.
- Metalloproteinases, particularly gelatinase, mediate local proteolysis for penetration.
- Cells migrate through the membrane via active locomotion and squeezing, with minimal destruction.
- Type I collagen fibers in connective tissue are displaced without degradation.
Conclusions:
- Leukocyte diapedesis involves a three-step process: adhesion, proteolysis, and migration.
- Metalloproteinase-mediated basement membrane degradation facilitates leukocyte extravasation.
- Leukocytes can penetrate connective tissue barriers without complete matrix destruction.