Differential neutrophil activation in viral infections: Enhanced TLR‐7/8‐mediated CXCL8 release in asthma

Abstract

Background and objectiveRespiratory viral infections are a major cause of asthma exacerbations. Neutrophils accumulate in the airways and the mechanisms that link neutrophilic inflammation, viral infections and exacerbations are unclear. This study aims to investigate anti‐viral responses in neutrophils from patients with and without asthma and to investigate if neutrophils can be directly activated by respiratory viruses.MethodsNeutrophils from peripheral blood from asthmatic and non‐asthmatic individuals were isolated and stimulated with lipopolysaccharide (LPS) (1 μg/mL), f‐met‐leu‐phe (fMLP) (100 nM), imiquimod (3 μg/mL), R848 (1.5 μg/mL), poly I:C (10 μg/mL), RV16 (multiplicity of infection (MOI)1), respiratory syncytial virus (RSV) (MOI1) or influenza virus (MOI1). Cell‐free supernatants were collected after 1 h of neutrophil elastase (NE) and matrix metalloproteinase (MMP)‐9 release, or after 24 h for CXCL8 release.Results LPS, fMLP, imiquimod and R848 stimulated the release of CXCL8, NE and MMP‐9 whereas poly I:C selectively induced CXCL8 release only. R848‐induced CXCL8 release was enhanced in neutrophils from asthmatics compared with non‐asthmatic cells (P < 0.01). RSV triggered the release of CXCL8 and NE from neutrophils, whereas RV16 or influenza had no effect.ConclusionNeutrophils release CXCL8, NE and MMP‐9 in response to viral surrogates with R848‐induced CXCL8 release being specifically enhanced in asthmatic neutrophils. Toll‐like receptor (TLR7/8) dysregulation may play a role in neutrophilic inflammation in viral‐induced exacerbations.

A novel immunomodulatory function of neutrophils on rhinovirus-activated monocytes in vitro

“…34 35 Our previous work has shown that despite neutrophils expressing functional innate immune receptors for detecting RV, they are non-responsive to live RV16. 16 Neutrophil activation appears to be due to inflammatory mediators generated from other cells. 36 We know that the primary site of RV infection is the epithelium 37 38 and these cells could be the source of mediators that activate neutrophils.…”

“…However, when challenged with replication competent RV neutrophils did not respond with increased CXCL8, NE or MMP-9. 16 In contrast, structural airway cells 17 18 and monocytes do respond to RV. 19 In this study, we characterised the interaction between monocytes, neutrophils and RV.…”

“…16 Briefly, whole blood containing acid citrate dextrose as the anti-coagulant was mixed with 10% dextran (MP Biomedicals, Santa Ana, California, USA) to allow for red blood cell sedimentation. The upper layer was removed and overlayed on Ficoll Paque-PLUS (GE Healthcare, Little Chalfont, UK) and centrifuged at 490×g for 10 min.…”

Neutrophil-derived chemokines on the road to immunity

“…Much less is known about neutrophil responsiveness to viruses in terms of chemokine production. For instance, it has been reported that neutrophils treated in vitro with the human immunodeficiency virus transactivator protein (Tat) produce CXCL8 [58], while neutrophils incubated with Respiratory Syncytial Virus (RSV) produce and release also CCL3 [59] and CCL4 [60], in addition to CXCL8 [61], therefore disclosing their role as cells releasing potent inflammatory mediators during RSV-related bronchiolitis. Similarly, neutrophils exposed to Herpes Simplex Virus 1 (HSV-1)-infected corneal tissue were found to produce elevated CXCL9 levels [62], suggesting that they contribute to the attraction of CD4 + T cells/Th1 cells, which are essential for antiviral immunity.…”

Tumstatin fragment selectively inhibits neutrophil infiltration in experimental asthma exacerbation

“…We were further interested to see if other neutrophil functions such as CXCL8 (IL-8) secretion, degranulation and NETosis could be affected. CXCL8 secretion and neutrophil elastase release were stimulated with R848 (a Toll-like receptor 7/8 ligand, 33 ) in the presence of SP17 and CP17, but no significant effect on these functions was observed ( Figure S1C,D). We also investigated the possibility of an effect on neutrophil extracellular DNA trap formation (NET) as it has been shown that ROS production plays a critical role in NET formation.…”