LPS INDUCED AND AGE RELATED NEUTROPHILIC INFLAMMATION IN ASTHMA

Abstract

BACKGROUND: Asthma is a multidimensional syndrome made up of a range of 'phenotypes'. Neutrophilic inflammation is one of these phenotypes. Neutrophilic asthma is linked to increased asthma severity, an increased likelihood of exacerbating and a reduced response to therapy.AIMS: The aim of this project was to investigate the pathogenesis, reproducibility and consequences of neutrophilic inflammation in asthma. The following were investigated: (1) the effect of onset age of asthma on sputum neutrophil counts (2) the reproducibility and validity of sputum neutrophil counts in moderate to severe asthmatics (3) the possible effect of LPS challenge in causing airway neutrophilia in moderate asthmatics, CXCL8 release from alveolar macrophages and possible corticosteroid resistant neutrophil chemotaxis.METHODS: (1) Clinical and inflammatory data of 19 early onset asthmatics and 19 late onset asthmatics were compared (2) The reproducibility of sputum neutrophils over the long (>2 months) and short term (7±1 days) was investigated in 14 moderate to severe asthmatics (3) Inhaled LPS was administered to 7 moderate asthmatics: Serial clinical measurements were taken to observe the safety of LPS inhalation. Sputum (n=7) and BAL samples (n=7) were analysed to observe the effects of LPS inhalation on the central and peripheral airways. Alveolar macrophages were obtained during bronchoscopy and cultured ex vivo (n=4).RESULTS: (1) There were increased neutrophil counts in LOA asthmatics compared to those with EOA. LOA subjects had better asthma control representative of increased lung function and reduced ACQ scores (2) sputum neutrophil counts suggested good reproducible value over both long and short term time periods. 90% power calculations were performed for parallel and cross over studies (3) Significant decreases in lung function were observed at 0.5, 1, 2 and 3 hours post LPS, significant increases in temperature post 6 and 8 hours and an observable increase in exhaled nitric oxide levels. There was no associated changes in steroid sensitivity pre and post LPS. Reduced CXCL8 and TNF release was observable (but not statistically significant) post ex vivo LPS stimulation.CONCLUSIONS: (1) Duration of asthma rather than age of onset of asthma is a key predictor of lung function. Raised sputum neutrophil counts are phenotypic to LOA but they do not indicate it as a biomarker of severe disease as previously described. (2) Sputum neutrophils are a repeatable and reliable endpoint, with good long and short term repeatability. Sputum monitoring during treatment steps could prove more effective based on downstream suppression (3) LPS inhalation has been shown to be a safe inducer of neutrophilic inflammation. No reported changes in steroid response were observed following LPS induced neutrophilia. Alveolar macrophage derived CXCL8 and TNF are tolerant cytokines following ex vivo LPS stimulation.

Date of Award	1 Aug 2013
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Sukh Singh (Supervisor) & Jonathan Plumb (Supervisor)