Investigating neutrophil dysfunction in COVID-19, underlying disease mechanisms and relationship to clinical outcomes

Thein, Onn Shaun ORCID: 0000-0003-0524-9449 (2024). Investigating neutrophil dysfunction in COVID-19, underlying disease mechanisms and relationship to clinical outcomes. University of Birmingham. Ph.D.

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Abstract

Coronavirus disease 2019 (COVID-19) caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) caused a world-wide pandemic in March 2020. Since first identified, over 30 different variants have been identified, with dominant strains causing waves of infection mirrored in hospital admissions and mortality. Rapid collaborative research into understanding the host-virus interactions and to develop treatment strategies led to repurposing of several therapeutics to improve patient outcomes.

The innate immune system is the first-line cellular defence against pathogens, and responsible for the initiation, maintenance and recruitment and resolution of inflammation. Disruption to any point of this process can lead to an inadequate response, either with insufficient recruitment of cells or prolonged inflammation. Neutrophils are involved with all these processes and represent the largest leucocyte subpopulation.

This thesis aimed to investigate the role of neutrophils in COVID-19 infection, to determine how their function was altered in disease and how this correlated with clinical outcomes. By investigating the effect of inhibitory molecules and therapeutics, we investigated the potential pathways that may be disrupted leading to altered neutrophil function. Viral evolution and the changes to the clinical phenotype are important to note as this may affect therapeutic efficacy, and this thesis compared neutrophil effector functions between alpha, delta and omicron variant COVID-19 patients.

Neutrophil effector functions such as phagocytosis, migration and neutrophil extracellular trap formation were examined, in addition to surface marker expression. All experiments were adapted for investigator safety with a novel infectious disease, and these were validated to demonstrate equivalency. Clinical data and outcome measures (e.g. length of hospital stay, long- and short-term mortality) from recruited patients and age-matched controls were collected to correlate to any changes in neutrophil effector functions.

Compared to age matched controls and community acquired pneumonia patients, neutrophils isolated from alpha variant patients demonstrated decreased phagocytosis, with reduced nuclear/ mitochondrial reactive oxygen species generation, increased migration, increased neutrophil extracellular trap formation (NETosis) and altered surface marker expression. This constellation of changes could suggest pseudopod dysfunction related to phosphoinositide 3-kinase (PI3K) signalling, but inhibition of PI3K did not restore function in COVID-19 neutrophils. Similarly, there was no improvement with the use of treatments affecting neutrophil elastase, which may account for increased migration.
Neutrophils isolated from patients with omicron COVID-19 demonstrated decreased migration and NETosis compared to alpha variant COVID-19. Surface marker expression was unique to omicron compared to alpha variant neutrophils and there was a decrease in circulating vascular endothelial growth factor and myeloperoxidase with increased interleukin-6.

The neutrophil dysfunction seen in alpha variant patients did not persist to omicron variant patients which correlates to the less severe clinical phenotype observed. This data presented in this thesis supports the hypothesis that neutrophil dysfunction COVID-19 contributes to the clinical symptoms observed. The treatments and pathway inhibitors investigated here did not restore neutrophil function, suggesting a mechanism separate to PI3K signalling and neutrophil elastase activity. The differences in function and clinical data seen between SARS-CoV-2 strains suggests further investigation into currently recommended COVID-19 treatments is required to determine their efficacy with the evolving disease.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):