Nontypeable Haemophilus influenzae-Induced Inflammation, Corticosteroids Unresponsiveness and Functional Polarisation in COPD Alveolar Macrophages

UoM administered thesis: Phd

  • Authors:
  • Rana Khalaf

Abstract

COPD is a chronic inflammatory disease of the airways where many patients have recurrent lower airway bacterial infection, most commonly nontypeable Haemophilus influenzae (NTHi). Corticosteroids are commonly used anti-inflammatory drugs in COPD with limited clinical benefit. Previous studies focused on corticosteroid responsiveness in COPD did not consider the role of airway NTHi infection. Alveolar macrophages are the main inflammatory cells in COPD pathogenesis, a shift in their phenotype was highlighted in COPD patients. Some bacteria can modify alveolar macrophage phenotype to persist in the lower airways.I have optimised a clinically relevant in vitro model of NTHi infection; human alveolar macrophages were stimulated with an increasing load of live NTHi clinical isolate (R2846). NTHi provoked time-dependent release of TNF-alpha, IL-6, CXCL8 and IL-10 from alveolar macrophages, which was correlated with bacterial growth, lysis and phagocytosis in the model. Furthermore, NTHi load was inversely correlated with IL-10 release. These findings suggest that NTHi infection is a dynamic inflammatory process in human alveolar macrophages and pointed to the possible role of IL-10 in the NTHi persistence in the lower airways.NTHi-induced cytokines in alveolar macrophages showed reduced corticosteroid responsiveness, CXCL8 was particularly corticosteroid unresponsive cytokine. NTHi-induced glucocorticoid receptor (GR) phosphorylation at ser 226 residue, which would encourage GR nuclear exportation. This might be one possible mechanism of reduced corticosteroid response in the model. In line with the latter finding, NTHi impaired the corticosteroid-induced GR nuclear localisation, which was partially reversed by p38 MAPK inhibitor (BIRB-796). These results suggest the role of NTHi in corticosteroid unresponsiveness in COPD alveolar macrophages. NTHi-induced cytokine release in alveolar macrophages was mediated by NF-kappaB, p38 and ERK MAPK pathways. Combination of corticosteroid (dexamethasone) with p38 and ERK MAPK inhibitors (BIRB-796 and AZD6244 respectively) showed a potential synergistic anti-inflammatory effect in the model. Therefore, inhibitors of MAPK pathways might serve as future anti-inflammatory therapies in NTHi-infected COPD patients. NTHi in vitro infection caused upregulation of the pro-inflammatory (TNF-alpha, CXCL8, CD38) and the anti-inflammatory (IL-10) markers' mRNA levels in COPD alveolar macrophages. Meanwhile, NTHi downregulated the antigen-presentation molecule (HLA-DR) and the scavenger receptors (CD14, CD36, CD163 and CD206) mRNA levels in COPD alveolar macrophages. Moreover, sputum macrophages from NTHi-infected stable COPD patients showed lower mRNA levels of CD36 and HLA-DR. These findings suggest that the NTHi modification of alveolar macrophage functions, especially antigen presentation and efferocytosis, might be a possible mechanism of NTHi chronic infection and COPD disease progression.

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Original languageEnglish
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Award date1 Aug 2016