Background: Granulocyte–macrophage colony-stimulating factor (GM-CSF) has been implicated as an important mediator in the pathogenesis of asthma and chronic obstructive pulmonary disease (COPD). However, the expression of GM-CSF and its receptor in airway samples in asthma and COPD across disease severity needs to be further defined. Methods: Sputum GM-CSF was measured in 18 control subjects, 45 subjects with asthma and 47 subjects with\ud COPD. Enumeration of GM-CSF+ cells in the bronchial\ud submucosa and airway smooth muscle bundle was\ud performed in 29 control subjects, 36 subjects with\ud asthma and 10 subjects with COPD.\ud Results: The proportion of subjects with measurable GMCSF\ud in the sputum was raised in those with moderate (7/\ud 14) and severe (11/18) asthma, and in those with COPD\ud GOLD (Global Initiative for Chronic Obstructive Lung\ud Disease) stage II (7/16), III (8/17) and IV (7/14) compared\ud with controls (1/18) and those with mild asthma (0/13);\ud p=0.001. The sputum GM-CSF concentration was\ud correlated with the sputum eosinophilia in subjects with\ud moderate to severe asthma (rs=0.41; p=0.018). The\ud median (interquartile range) GM-CSF+ and GM-CSFR+\ud cells/mm2 of submucosa was increased in severe asthma\ud (1.4 (3.0) and 2.1 (8.4)) compared with those with mild to\ud moderate asthma (0 (2.5) and 1.1 (5)) and healthy\ud controls (0 (0.5) and 0 (1.6)), (p=0.004 and p=0.02,\ud respectively).\ud Conclusions: The findings support a potential role for\ud GM-CSF in asthma and COPD and suggest that overexpression\ud of GM-CSF in sputum and the bronchial\ud mucosa is a particular feature of severe asthma
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