Innate immunity and its link to clinical outcomes in smokers with and without COPD

Chronic obstructive pulmonary disease (COPD) is the fourth most common causes of death globally, affecting around ten percent of the adult population. Patients with COPD often suffer from comorbidities that are associated with impaired prognosis, among them chronic bronchitis, emphysema, cardiovascular diseases (CVD) and diabetes mellitus type II. Despite the clinical importance of COPD and its link to comorbidities, there is a limited understanding of the underlying pathogenic mechanisms, which hampers the efficacy of disease monitoring and therapy. Chronic neutrophilic inflammation is a common finding in COPD and several of its comorbidities, representing a feature that responds poorly to currently available therapy.

The main aim of this thesis was to characterize clinical and mechanistic aspects of neutrophilic inflammation in COPD and its comorbidities. For this reason, we utilized three human study materials, consisting of healthy non-smokers, smokers without COPD and smokers with COPD. Material 1 included an additional group of ex-smokers with COPD, while material 3 also required a diagnosis of concomitant chronic bronchitis for the COPD group. All study subjects underwent a thorough clinical and radiological investigation whereafter blood samples were harvested. Furthermore, in materials 1 and 3, lower airway samples, including bronchoalveolar lavage and protected bronchial brushes, were obtained during bronchoscopy, whereas sampling from the nasal cavity was provided as an option in material 1 only. Extracellular cytokine protein concentrations were quantified with ELISA, U- Plex® or PEA assays and cytokine expression in defined immune cells was determined using flow cytometry.

Paper I was based on study material 1 and addressed the involvement of local neutrophils in the production of the neutrophil-mobilising cytokine IL-26 in the lower airways of smokers with COPD. This paper forwards novel evidence that IL- 26 is expressed in lower airway granulocytes, predominantly consisting of neutrophils. This expression was decreased in smokers without and with COPD, compared with healthy non-smokers and ex-smokers with COPD. Furthermore, the expression of IL-26 in granulocytes of the lower airways correlated with more pronounced airway obstruction in smokers with COPD. In addition, the extracellular concentration of IL-26 protein in this group was increased in smokers with COPD, compared with healthy non-smokers, and correlated with decreasing gas diffusing capacity of the lungs. Finally, the presence of emphysema related to increased extracellular IL-26 protein concentration among smokers without and with COPD.

In Paper II, we investigated the local production of IL-26 by T lymphocytes in the nasal cavity of smokers with COPD. We found that both T-helper (Th: CD3+ CD4+) and T-cytotoxic (Tc: CD3+ CD8+) cells express intracellular IL-26. In the case of Th cells, this expression correlated with increased concentration of neutrophils in the lower airways of smokers with COPD. Moreover, when all current smokers were pooled as one group, IL-26 expression in Tc cells displayed a negative correlation with quality of life and dyspnoea. The latter was true even for Th cells. Finally, the nasal concentration of extracellular IL-26 protein was increased in smokers with COPD, and this increase was more pronounced in those without emphysema.

In Paper III, we addressed the association of different signs of local and systemic neutrophilic inflammation with glucose homeostasis in smokers with COPD. We found that fasting blood glucose was decreased in this group, and this decrease was correlated with higher protein concentration of the neutrophil-mobilising cytokine IL-36a in the lower airways. Additionally, smokers with COPD displayed a greater change in blood glucose during an oral glucose tolerance test, while a negative correlation was observed between glucose concentration at the end of this test and lower airway concentration of CXC motif chemokine ligand 10 (CXCL10), a chemokine that can be produced by neutrophils.

In Paper IV, we investigated alterations during COPD exacerbations in perceived molecular biomarkers of CVD that are related to neutrophils, among smokers with COPD and chronic bronchitis. We found that the protein concentration of oncostatin M (OSM) in serum increased in parallel with blood neutrophils, in stable disease. In addition, during acute exacerbations of COPD, the serum concentration of OSM protein was substantially increased and correlated in a positive manner with the corresponding concentrations of several other neutrophil-related perceived CVD biomarkers. At the same time, the serum concentration of OSM associated with decreasing blood oxygen levels and, therefore, with exacerbation severity.

In conclusion, this thesis forwards evidence that specific aspects of chronic neutrophilic inflammation, including IL-26, IL-36a, CXCL10 and OSM, are involved in COPD and/or the risk for developing its comorbidities. This provides a rationale for further investigating the clinical utility of these aspects as targets for disease characterisation, monitoring and/or therapeutic intervention.

List of scientific papers

I. Pournaras N*, Ramos-Ramírez P*, Bandeira E, Brundin B, Cardenas El, Che KF, Karimi R, Arebro J, Nyren S, Stjärne P, Cardell L-O, Sköld MC, Bossios A and Linden A. Expression of IL-26 protein in granulocytes from the lower airways of long-term smokers with mild to moderate COPD. [Manuscript]

II. Arebro J*, Pournaras N*, Ramos-Ramírez P, Cardenas EI, Bandeira E, Che KF, Brundin B, Bossios A, Karimi R, Nyrén S, Stjärne P, Sköld M, Linden A. Nasal production of IL-26 involving T cells in smokers with and without chronic obstructive pulmonary disease. J Allergy Clin Immunol. 2025 Mar 28:S0091-6749(25)00332-X. Epub ahead of print. https://doi.org/10.1016/j.jaci.2025.03.017

III. Pournaras N, Andersson A, Kovach MA, Padra M, Che KF, Brundin B, Yoshihara S, Bozinovski S, Linden SK, Jansson P-A, Sköld MC, Qvarfordt I, Linden A. Glucose homeostasis in relation to neutrophil mobilization in smokers with COPD. Int J Chron Obstruct Pulmon Dis. 2022 May 20;17:1179-1194. https://doi.org/10.2147/copd.s353753

IV. Cardenas EI*, Andelid K*, Pournaras N, Ekberg-Jansson Ann, Orsini N, Stratelis G, Jernberg T, Linden A. Serum proteomics links the cardiorespiratory biomarkers CTRC, OSM, and MMP-10 to exacerbation severity and number in patients with COPD. Clin Sci (Lond). 2025 May 7:CS20255852. Epub ahead of print. https://doi.org/10.1042/cs20255852

*These authors contributed equally to the corresponding work