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Title: Human cytomegalovirus and the neutrophil
Author: Pocock, Joanna Mary
ISNI:       0000 0004 7229 6998
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2018
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Human cytomegalovirus (HCMV) is a highly prevalent opportunistic infection and a major pathogen in immune-compromised patients. The virus exhibits a wide cell tropism and is able to lytically infect virtually any cell type, with detectable gene expression and release of new virions, but not the neutrophil. This cell is the first immune cell to engage most pathogens, engulfing and killing them before undergoing apoptosis and clearance by macrophages. However certain viruses and bacteria are able to evade host defences and use the neutrophil as a “Trojan horse” for replication and dissemination. In this context, enhanced neutrophil survival may promote infection. This work describes a profound neutrophil survival phenotype elicited by contact with live or UV-inactivated HCMV, in the absence of lytic viral gene expression. The effect does not involve signalling through candidate Toll-like receptors, but is dependent on activation of the ERK MAPK and NFκB signalling pathways, and is viral strain-dependent, restricted to clinical strains of the virus. Furthermore, HCMV triggers the secretion of a bioactive secretome that induces a similar paracrine anti-apoptotic effect in fresh neutrophils, and stimulates monocyte chemotaxis and differentiation to a phenotype that is permissive for HCMV infection. This “transferrable” effect is not due to residual virus or the presence of well-known neutrophil survival factors such as IL-6 or IL-8, but is mediated by a heat-stable protein or lipid, secreted late in culture. These results are supported by data in neutrophils isolated from patients with CMV viraemia and pneumonitis which show increased survival ex vivo, and will be further investigated using plasma membrane profiling by amino-oxybiotinylation and tandem mass tag mass spectrometry. This technique, used for the first time here in a primary cell type, allows quantitative proteomics to be performed for the first time in the neutrophil. This work demonstrates that the technique provides a comprehensive readout of all neutrophil plasma membrane proteins in a sample, with high plasma membrane purity and minimal neutrophil activation and necrosis, validated by flow cytometry. Furthermore, this has been applied to generate plasma membrane profiles for the resting, inflammatory and apoptotic neutrophil, revealing a number of neutrophil cell surface molecules not found by previous membrane proteomic methods. This technique has the potential to analyse the effect of HCMV and other pathogens on the expression profile of the neutrophil surface membrane and to examine how neutrophil signalling and function is modulated. These data shed light on the role of neutrophil apoptosis as a potential promoter of HCMV infection, and have the potential to increase our understanding of both the neutrophil’s response to pathogen invasion and to generate future approaches to combating HCMV dissemination and pathogenesis.
Supervisor: Chilvers, Edwin ; Cowburn, Andrew ; Reeves, Matthew Sponsor: Medical Research Council ; Addenbrooke's Charitable Trust
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
Keywords: Human cytomegalovirus ; neutrophil ; viral infection ; innate immunity ; plasma membrane profiling ; amino-oxybiotinylation