Inflammatory subtypes in asthma: assessment and identification using induced sputum.
OBJECTIVE
The authors sought to investigate the detection of non-eosinophilic asthma using induced sputum. Although this is an important subtype of clinical asthma, its recognition is not standardized.


METHODS
Adult non-smokers with asthma and healthy controls underwent sputum induction and hypertonic saline challenge. Non-eosinophilic asthma was defined as symptomatic asthma with normal sputum eosinophil counts. The normal range for sputum eosinophil count was determined using the 95th percentile from the healthy control group as a cut-off point.


RESULTS
The recognition of non-eosinophilic asthma using eosinophil proportion was in agreement with a definition based on absolute eosinophil count (kappa 0.67). Non-eosinophilic asthma was a stable subtype over both the short term (4 weeks) and longer term (5 years, kappa 0.77). Airway inflammation in asthma could be categorized into four inflammatory subtypes based on sputum eosinophil and neutrophil proportions. These subtypes were neutrophilic asthma, eosinophilic asthma, mixed granulocytic asthma and paucigranulocytic asthma. Subjects with increased neutrophils (neutrophilic asthma and mixed granulocytic asthma) were older and had an increased total cell count and cell viability compared with other subtypes.


CONCLUSIONS
Induced sputum eosinophil proportion is a good discriminator for eosinophilic asthma, providing a reproducible definition of a homogenous group. The remaining non-eosinophilic subjects are heterogeneous and can be further classified based on the presence of neutrophils. These inflammatory subtypes have important implications for the investigation and characterization of airway inflammation in asthma.
Simpson
Jodie L
JL
School of Medical Practice and Population Health, Hunter Medical Research Institute, The University of Newcastle, Callaghan, New South Wales, Australia.
Scott
Rodney
R
Boyle
Michael J
MJ
Gibson
Peter G
PG
D000328:Adult; D000368:Aged; D000402:Airway Obstruction / Q000276:immunology; D000704:Analysis of Variance; D001249:Asthma / Q000145:classification* / Q000276:immunology*; D016022:Case-Control Studies; D004804:Eosinophils / Q000378:metabolism*; D005260:Female; D006098:Granulocytes / Q000378:metabolism; D006801:Humans; D007958:Leukocyte Count; D008297:Male; D008875:Middle Aged; D009504:Neutrophils / Q000378:metabolism*; D015203:Reproducibility of Results; D013183:Sputum / Q000276:immunology*