Use this URL to cite or link to this record in EThOS: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.649799
Title: Modulation of human neutrophil apoptosis by tumour necrosis factor-alpha
Author: Dunlop, J.
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1998
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Abstract:
Many pro-inflammatory mediators have been demonstrated to inhibit neutrophil apoptosis in vitro, suggesting that such agents act not only in a priming or secretagogue capacity but also increase neutrophil functional longevity by delaying apoptosis. We have examined whether this hypothesis holds true for all neutrophil priming agents, in particular TNFα, a potent neutrophil priming agent which has been variably reported to either induce, delay, or have no effect on the rate of constitutive neutrophil apoptosis. We have shown that following a 20 hr incubation the rate of neutrophil apoptosis is inhibited by TNFα, however more detailed analysis demonstrated the ability of this cytokine to promote apoptosis in a subpopulation of cells at earlier (2-8 hr) times. FMLP, PAF, inositol hexakisphosphate, LPS, LTB and GM-CSF which represent a broad spectrum of alternative neutrophil priming and activating agents all inhibited apoptosis at 6 and 20 hr. The early pro-apoptotic effect of TNFα was confirmed by DNA fragmentation and propidium iodide binding and shown to be concentration-dependent with a near-identical EC50 value (2.8 ng/ml) to that observed for TNFα-priming of fMLP-stimulated superoxide anion generation. Moreover, the early cytocidal effect of this cytokine was detectable within 2 hr, abolished by TNFα neutralizing antibody, and was not associated with any change in cell viability or recovery. Of note, TNFα-stimulated apoptosis was abolished by pre-incubation of neutrophils with selective blocking antibodies to both the TNFR55 (which contains the classical death-domain sequence and is entirely responsible for the TNFα priming effect in suspension neutrophils) and TNFR75 receptor subtypes. Moreover, the TNFR55-selective mutants (E146K, R23W-S86T) induced neutrophil apoptosis but with a potency 14-fold lower than wild type TNFα while the TNFR75-selective mutant (D143F) did not induce apoptosis. These data indicate that TNFα has the ability apparently unique to this priming agent to induce apoptosis in human neutrophils at early time points via a mechanism whereby the TNFR75 facilitates and permits TNFR55-mediated induction of cell death.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.649799  DOI: Not available
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