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Direct cytotoxicity of polymorphonuclear leukocyte granule proteins to human lung-derived cells and endothelial cells
D G Okrent1, A K Lichtenstein, T Ganz
1Will Rogers Institute Pulmonary Research Laboratory, Department of Medicine, UCLA School of Medicine.
Abstract:
Neutrophils, in the course of defending the host against microbial invasion, release a potent arsenal of proteins that can potentially damage host tissues. Defensins are major peptides of human polymorphonuclear leukocyte (PMN) granules and are both broadly microbicidal and cytotoxic to several tumor cell lines. To determine whether these peptides could play a role in neutrophil-mediated lung injury, we examined the cytotoxicity of defensins and other PMN granule proteins in a chromium release assay with human lung-derived cell lines MRC-5 (lung fetal fibroblast), A549 (lung adenocarcinoma with features of alveolar epithelium), and primary cultures of human umbilical vein endothelial cells (HUVEC). Crude fractionation of an acid extract of human PMN granules yielded four fractions A-D. Only fraction D (containing mostly defensins) was significantly cytotoxic to all three target cells. In contrast, fraction A (containing myeloperoxidase and lactoferrin) and fraction C (containing lysozyme) had little effect, and fraction B (containing chiefly cathepsin G and elastase) was only injurious to endothelial cells. The cytotoxicity of whole PMN granule extracts on pulmonary epithelial and fibroblast targets could be completely accounted for by their defensin content. Fraction D- and defensin-mediated cytotoxicity was concentration dependent, required at least 10 to 12 h to become manifest, and was inhibited by serum. The role of these peptides in lung damage during acute and chronic inflammation deserves further study.
Insights
Defensins, key peptides from human polymorphonuclear leukocytes (PMN), cause significant lung cell damage. This study confirms defensins are the primary cause of PMN-mediated lung injury, highlighting their role in inflammatory lung diseases.
Area of Science:
- Cell Biology
- Immunology
- Toxicology
Background:
- Neutrophils defend against microbes but can harm host tissues with released proteins.
- Defensins are microbicidal and cytotoxic peptides found in human polymorphonuclear leukocyte (PMN) granules.
Purpose of the Study:
- To investigate the role of defensins and other PMN granule proteins in neutrophil-mediated lung injury.
- To assess the cytotoxicity of PMN granule fractions on human lung-derived cells.
Main Methods:
- Utilized a chromium release assay to measure cytotoxicity.
- Examined human lung fibroblast (MRC-5), lung adenocarcinoma (A549), and umbilical vein endothelial cells (HUVEC).
- Crude fractionation of human PMN granule extracts into four fractions (A-D).
Main Results:
- Fraction D, rich in defensins, was significantly cytotoxic to all tested lung cell types.
- Other fractions (A, B, C) showed limited or specific cytotoxicity (e.g., fraction B on endothelial cells).
- Defensin-mediated cytotoxicity was concentration-dependent, time-delayed (10-12h), and serum-inhibited.
Conclusions:
- Defensins are the primary mediators of PMN granule extract cytotoxicity against pulmonary epithelial and fibroblast cells.
- The findings suggest defensins play a significant role in lung damage during acute and chronic inflammation.
- Further research is warranted to explore the precise role of defensins in inflammatory lung conditions.