Enhanced airway hyperresponsiveness in asthmatic children and mice with A(H1N1)pdm09 infection

Abstract

Background Severe asthma exacerbation is an important comorbidity of the 2009 HIN1 pandemic (A(H1N1)pdm09) in asthmatic patients. However, the mechanisms underlying severe asthma exacerbation remain unknown. In this study, airway hyperresponsiveness (AHR) was measured in pediatric asthma patients infected with A(H1N1)pdm09. We also evaluated AHR in asthmatic mice with A(H1N1)pdm09 infection and those with seasonal influenza for comparison. Methods AHRs in asthmatic children were defined as the provocative acetylcholine concentration causing a 20% reduction in forced expiratory volume in 1 s (PC20). To investigate the pathophysiology using animal models, BALB/c mice aged 6‐8 weeks were sensitized and challenged with ovalbumin. Either mouse‐adapted A(H1N1)pdm09, seasonal H1N1 virus (1 × 105 pfu/20 μl), or mock treatment as a control was administered intranasally. At 3, 7, and 10 days after infection, each group of mice was evaluated for AHR by methacholine challenge using an animal ventilator, flexiVent. Lung samples were resected and observed using light microscopy to assess the degree of airway inflammation. Results AHRs in the children with bronchial asthma were temporarily increased, and alleviated by 3 months after discharge. AHR was significantly enhanced in A(H1N1)pdm09‐infected asthmatic mice compared to that in seasonal H1N1‐infected mice (p < .001), peaking at 7 days postinfection and then becoming similar to control levels by 10 days postinfection. Histopathological examination of lung tissues showed more intense infiltration of inflammatory cells and severe tissue destruction in A(H1N1)pdm09‐infected mice at 7 days postinfection than at 10 days postinfection. Conclusion Our results suggest that enhanced AHR could contribute to severe exacerbation in human asthmatic patients with A(H1N1)pdm09 infection.

Histological characteristics of matrix metalloproteinase‐9 and tissue inhibitor of metalloproteinases‐1 in asthmatic murine model during A(H1N1)pdm09 infection

“…9,10 We previously reported that unlike seasonal influenza A H1N1 infection, A(H1N1) pdm09 infection in a murine model of asthma induces severe pulmonary inflammation on day 7 after infection. [11][12][13][14] Furthermore, in asthmatic mice with A(H1N1)pdm09 infection, interleukin-6 and tumor necrosis factor-α levels peak earlier on day 3 postinfection and with higher values compared to those in asthmatic mice with seasonal influenza (A/Puerto Rico/8/34, A/PR/8/34) infection. 13 Moreover, virus titers in bronchoalveolar lavage (BAL) fluid after influenza infection showed the highest levels in A(H1N1)pdm09-infected asthmatic mice on days 3 and 7 post-infection, and immunohistochemical finding stained with influenza A nucleoprotein (InfA-NP) revealed that InfA-NP was high expressed at site of pneumonia in A(H1N1)pdm09 infection.…”

“…A(H1N1)pdm09 infection, but not A/PR/8/34 infection, induces severe pulmonary inflammation in the murine model of asthma on day 7 after infection. [11][12][13][14] The pathological findings revealed remarkable inflammatory cell infiltration and abscess formation with reduced area of air space in the alveola of Asthma/A(H1N1)pdm09-infected mice (p < 0.05; Figure 1a,b).…”

“…To establish the bronchial asthma model, the mice were sensitized and challenged with Grade II ovalbumin (OVA; Sigma-Aldrich), as previously described. [11][12][13][14] The study was approved by the All Institutional Animal Care and Use Committee of Yamaguchi University (No. 29-S01) and all methods were conducted in accordance with the approved guidelines.…”

“…13 Also, the airways in A(H1N1)pdm09-infected asthmatic mice showed greater hyperresponsiveness compared to those of A/PR/8/34 infection. 14 Matrix metalloproteinases (MMPs) are proteinases that belong to a large family of zinc-containing enzymes responsible for degrading extracellular matrix components, such as collagen and proteoglycans, during tissue remodeling. [15][16][17] matrix metalloproteinase-9 (MMP-9) is mainly produced by macrophages and neutrophils, but also epithelial cells, mast cells, fibroblasts, and smooth myocytes.…”