Cigarette smoke is the leading cause of preventable mortality worldwide. This excess death is attributable to an increased risk of acquiring a variety of conditions, including chronic respiratory/cardiovascular diseases and various types of cancer. Smokers are additionally predisposed to develop infectious diseases, notably including pneumonia caused by the influenza virus, one of the most prevalent and burdensome pathogens in existence today. Although cigarette smoke is well known to modulate many aspects of the immune system, the specific mechanisms by which this predisposition is mediated are incompletely understood. Also unclear is the effect of cigarette smoke on responses to intranasal immunization strategies aimed at eliciting immunity against pathogens such as influenza in the upper airways, where protection may substantially contribute to sterilizing immunity.
This PhD thesis focused primarily on addressing these knowledge gaps. In the first study, we assessed the effect of cigarette smoke on antibody induction following intranasal immunization in the upper airways of mice, finding that smoke exposure attenuated antigen-specific IgA induction in the upper respiratory tract, reproductive tract, and systemic circulation. In addition, we found that these nasal IgA demonstrated a reduced antigen-binding avidity in the acute post-immunization period. Mechanistically, deficits in nasal IgA were associated with a reduced accumulation of antigen-specific IgA antibody-secreting cells (ASCs) in the nasal mucosa, induction of these cells in nasal-draining lymphoid tissues, and upregulation of molecules critical to ASC homing (vascular cell adhesion molecule-1; VCAM-1) and IgA transepithelial transport (polymeric immunoglobulin receptor; pIgR) in the nasal mucosa. Ultimately, in tandem with recent clinical work published by others, our study strongly suggests that cigarette smoke can attenuate IgA induction in the upper airways, which may have implications for aspects of intranasal vaccine efficacy. Thus, smoking status should be more consistently considered in the design of clinical trials for IgA-oriented intranasal vaccines.
The second study did not assess smoking and host defense directly, but rather served to optimize protocols for assessing immunoglobulins in human mucoid respiratory samples as a precursor to future studies in smoking-related disease. In this regard we found that, relative to phosphate-buffered saline (PBS), dithiothreitol (DTT)-based processing of human sputum samples increased total IgA yields, decreased IgE yield, and improved the detection of a specific IgG autoantibody. These findings suggest that processing choices for human mucoid respiratory samples should be made with specific goals in mind as they pertain to antibody isotype(s) of interest.
Finally, in the third study we investigated potential mechanisms by which cigarette smoke exposure promotes influenza, given that smokers are at increased risk of acquiring the pathogen, progressing to severe disease, and being admitted to hospital/ICU following infection. In doing so, we found that concurrent smoke exposure increased morbidity, hypoxemia, pulmonary edema, neutrophilia, and ultimately mortality in a mouse model of H1N1 infection. These changes were associated with an increased accumulation of viral (v)RNA in cells independent of any change in the shedding of replication-competent viral particles. Using a novel dysregulation score approach, we found that interleukin (IL)-6 and colony-stimulating factor (CSF)3 expression was highly exacerbated in the lungs and circulation of smoke-exposed, infected mice relative to controls. Supplementation of recombinant (r)CSF3 increased morbidity, hypothermia and edema, while blockade of the cognate receptor (CSF3R) improved alveolar-capillary barrier function. On the cellular level, single cell RNA-sequencing revealed a shift in the distribution of Csf3+ cells towards neutrophils. Finally, deep transcriptional analysis of neutrophils revealed a gene signature that was largely indicative of an exacerbated form of typical disease with select unique regulatory elements. Ultimately, this work identifies potential therapeutic targets (CSF3R signaling, excess vRNA accumulation) for the treatment of cigarette smoke-augmented influenza, and warns against clinical rCSF3 therapy to treat neutropenia during viral infectious disease.
In conclusion, the work presented in this PhD dissertation expands our understanding of the relationship between cigarette smoke and antimicrobial host defense as it pertains to both IgA immunity in the upper airways, and the pathogenesis of cigarette smoke-augmented influenza. / Thesis / Doctor of Philosophy (PhD) / Cigarette smoke exposure is well known to have many harmful effects on human health, including through its ability to promote various infectious diseases such as influenza. However, the mechanisms by which it promotes infection are not fully known. This is an important knowledge gap given that over 1.1 billion individuals continue to smoke worldwide, and a large number of people are exposed to the harmful effects of second-hand smoke, both with fatal consequence. The central goal of this thesis was to gain a better understanding of this relationship between cigarette smoke and infectious disease, specifically by assessing how smoke exposure impacts immune responses in the upper and lower airways.
In the first study, we found that smoke exposure interferes with the ability to activate immunoglobulin (Ig)A antibody responses in the nasal passages of mice, which may have important implications for human nasal vaccination strategies. The second study investigated different methods with which to best measure antibodies in human respiratory samples. Finally, in the third study we defined a role for a specific molecule, CSF3, in worsening health in a mouse model of concurrent cigarette smoke and influenza infection. Overall, this work provides new insights into the ways in which smoking can increase the risk of respiratory infection, thereby informing the future design and testing of vaccines and treatments for use in our highly smoke-exposed global population.
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/26898 |
| Date | January 2021 |
| Creators | McGrath, Joshua Jakob Charles |
| Contributors | Stampfli, Martin, Medical Sciences |
| Source Sets | McMaster University |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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