Impact of Cigarette Smoke Exposure on the Lung Fibroblastic Response after Influenza Pneumonia

Abstract

Influenza viruses can result in significant lung injury with significant morbidity and mortality. In this study, we evaluated the impact of cigarette smoke (CS) exposure on the pulmonary fibroblastic response after influenza infection. We used a murine model in which animals were exposed to CS or room air and subsequently infected with H1N1 influenza virus. Inflammatory and fibrotic responses were measured at different time points after influenza infection. Primary fibroblasts were isolated from the lungs of mice and their characteristics were evaluated. Exposure to CS significantly increased the amount of collagen in the lungs of mice infected with influenza virus compared with the nonsmoking group at 30 days after infection. Furthermore, the presence of fibroblast-specific protein-positive cells increased in the lungs of influenza-infected mice that were exposed to CS compared with the infection-alone group. The smoking group also showed delays in weight recovery and higher cell counts in BAL fluid after infection. Active transforming growth factor β1 levels in BAL fluid increased in both groups; however, CS-exposed mice had a later surge in active transforming growth factor β1 (Day 24). Ex vivo cultures of lung-derived fibroblasts from CS-exposed mice with influenza infection showed rapid proliferation, increased expression of α-smooth muscle actin-stained stress fibers, and higher expression of growth factors compared with fibroblasts from room air-exposed lungs after infection. These results suggest that CS exposure changes the fibroblastic potential, leading to increased fibrosis after influenza infection.

Effects of Cigarette Smoking on Influenza Virus/Host Interplay

“…Similarly, Hong et al noted that, with H3N2 at 25 TCID50 with 3 month CS exposure, CS exposed mice had 100 fold higher live virus titers at 10 dpi vs. the no CS controls, suggesting viral clearance had been impeded [37]. Interestingly, Lee et al has shown, using PR8 IAV at 100 PFU per mouse with 2 weeks CS exposure, that early viral titers at three days post infection were higher in CS mice vs controls, but peak viral titers and post peak clearance for CS and controls were identical in contrast to previous studies [38]. While seemingly conflicting, we would assume that these conflicting clearance results are more potentially due to variability in IAV dose, CS exposure, and viral genotype rather than being in direct contradiction.…”

“…However, in cigarette mouse models, IAV infection results in worse disease outcomes compared to non-smoking controls. For example, CS exposure and subsequently infection typically will result in reduced weight gain post infection [34][35][36][37][38], increased lung remodeling (deposition of scar tissue replacing functional lung tissue) [39,40] and increased mortality [33,[35][36][37]41] compared to non-CS infected mice. Similarly, CS exposure in humans is shown to be associated with increased risk of influenza infections [4,42,43], increased risk of severe symptoms [4], and decreased efficacy of influenza vaccine [44,45].…”

“…In contrast, chronic CS exposure (>2 weeks) results in exaggerated cytokine responses (TNF-α, IFN-y, IL-6, IL-12, IL-23, IL-1, IL-5, IL-10, KC, MIP-1a, IL-17, IL-1B) [36,37,40,41,54] with infection compared to non-smoking infected controls. In addition to elevated cytokine profiles, chronic exposure is also associated with increased local pulmonary inflammation including increased lung tissue and BALF neutrophils [34,37,38,40,41,58], macrophages [34,38,40,41,60,63], and lymphocytes [40,60,63] compared to non-CS exposed animals.…”

Influenza virus and SARS-CoV-2: pathogenesis and host responses in the respiratory tract

“…Comorbid chronic health conditions, including metabolic syndrome 39 , heart failure 40 and chronic obstructive pulmonary disease 41 , also increase an individual's risk of severe disease. Finally, environmental factors, such as cigarette smoke exposure, contribute to disease severity 42 , potentially as a result of alterations in epithelial and immune cell function 43 as well as in fibroblast repair responses to viral infection 44 .…”

Abnormal respiratory progenitors in fibrotic lung injury

“…Lung fibrosis was developed in some cases post-H1N1 influenza viral infection [ 60 ]. Chronic lung disease patients with frequent exacerbations of influenza infection subsequently developed fibrotic interstitial lung disease [ 61 ]. Following H1N1 influenza viral infection, an expansion of distal airway stem cells (DASC) expressing BC markers Trp63 and Krt5 assembled into nascent alveoli at sites of interstitial lung inflammation.…”