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Tumor necrosis factor enhances the neutrophil-dependent increase in endothelial permeability
1Department of Physiology and Cell Biology, Albany Medical College of Union University, New York 12208.
Abstract:
We examined the effect of tumor necrosis factor alpha (TNF alpha) on the increase in pulmonary microvascular endothelial monolayer permeability induced by activated neutrophils (PMN). Layering of PMN onto endothelial monolayers followed by activation of PMN with phorbol 12-myristate 13-acetate (PMA) increased 125I-albumin clearance rate across the monolayers. Pretreatment of endothelial monolayers for 6 hr with TNF alpha (200 U/ml) potentiated the PMN-dependent increase in endothelial permeability, whereas 1 hr or 6 hr pretreatment of endothelial monolayers with 200 U/ml and 100 U/ml, respectively, TNF alpha did not enhance the response. Adherence of PMN to the endothelial cells was increased at 1 and 6 hr after TNF alpha (200 U/ml) treatment, but the adherence response was markedly greater following 6 hr of TNF alpha. The TNF alpha treatment of endothelial cells did not enhance neutrophil activation responses to PMA. Pretreatment of PMN with IB4, a MAb to the CD18 integrin, the common beta subunit of the adhesion proteins LFA-1, Mac-1, and p150,95 of PMN, reduced the increases in PMN adherence and the endothelial monolayer permeability induced by the 6 hr TNF alpha treatment. In contrast, pretreatment of PMN with OKM-1, a MAb to the CD11b epitope (alpha-subunit), had no effect on the adherence and the potentiation of the increase in permeability. The potentiation of the PMN-dependent permeability increase and enhanced endothelial adhesivity at 6 hr after TNF alpha priming of endothelial cells was dependent on protein synthesis. The results indicate that protein synthesis-dependent expression of an endothelial ligand for CD18 and resultant endothelial hyperadhesiveness potentiates the PMN-mediated increase in endothelial permeability after TNF alpha activation of endothelial cells. The priming of endothelial cells by TNF alpha may be a critical step in the mediation of endothelial injury.
Insights
Tumor necrosis factor alpha (TNF alpha) primes endothelial cells, increasing pulmonary microvascular permeability by enhancing neutrophil adherence. This effect, mediated by CD18 integrins and protein synthesis, is crucial for TNF alpha-induced endothelial injury.
Area of Science:
- Pulmonary vascular research
- Cellular immunology
- Inflammation biology
Background:
- Pulmonary microvascular endothelial permeability increases with activated neutrophils (PMN).
- Tumor necrosis factor alpha (TNF alpha) is implicated in inflammatory responses.
Purpose of the Study:
- To investigate the effect of TNF alpha on PMN-induced pulmonary microvascular endothelial permeability.
- To elucidate the mechanisms underlying TNF alpha-mediated potentiation of endothelial permeability.
Main Methods:
- Endothelial monolayers were treated with TNF alpha and exposed to activated PMN.
- 125I-albumin clearance measured monolayer permeability.
- PMN adherence was quantified.
- Monoclonal antibodies (MAbs) IB4 (anti-CD18) and OKM-1 (anti-CD11b) were used.
- Protein synthesis inhibition was employed.
Main Results:
- 6-hour TNF alpha pretreatment potentiated PMN-induced permeability increase.
- TNF alpha increased PMN adherence to endothelial cells in a time-dependent manner.
- Anti-CD18 MAb IB4, but not anti-CD11b MAb OKM-1, reduced PMN adherence and permeability.
- The potentiation effect was dependent on protein synthesis.
Conclusions:
- TNF alpha primes endothelial cells, leading to protein synthesis-dependent expression of a CD18 ligand.
- This enhances PMN adherence and potentiates PMN-mediated increases in pulmonary microvascular permeability.
- TNF alpha-induced endothelial hyperadhesiveness is a key step in endothelial injury.