Interleukin-18 levels in induced sputum are reduced in asthmatic and normal smokers.
BACKGROUND
IL-18 is a cytokine which is known to have an important role in the development of a Th1 lymphocyte response. As such, it may have a regulatory role in asthma by modifying Th2 lymphocyte responses. Cigarette smoking may amplify the airway inflammation associated with asthma.


OBJECTIVE
This study investigated if IL-18 could be detected in induced sputum from asthmatics and normal subjects and if smoking altered IL-18 levels.


METHODS
Induced sputum was obtained from asthmatic (31 smokers, 35 non-smokers) and normal (20 smokers, 20 non-smokers) subjects. All smokers had a smoking history of > or =15 pack years. IL-18 levels in sputum supernatant were measured by ELISA. IL-18 mRNA expression and cellular localization were assessed by quantitative PCR and immunocytochemistry, respectively.


RESULTS
Smoking was associated with a significant reduction in IL-18 levels (median (interquartile range) - smokers 20 (0-102) pg/mL vs. non-smokers 358 (50-876) pg/mL, P<0.001). This was more pronounced in asthmatics (smokers, 47 (40-64) pg/mL vs. non-smokers, 530 (30-1484) pg/mL; P<0.001) than in normal subjects (smokers, 25 (0-78) pg/mL vs. non-smokers, 247 (50-656) pg/mL; P<0.01). Within each of the smoking and non-smoking groups there was no significant difference in IL-18 levels between asthmatic and normal subjects. There was no correlation between sputum IL-18 levels and any specific cell type in the sputum samples nor serum IgE levels. IL-18 mRNA expression was reduced in asthmatic smokers compared with non-smokers. IL-18 production was localized to sputum macrophages by immunocytochemistry.


CONCLUSIONS
IL-18 is detectable in induced sputum samples from both asthmatic and normal subjects. Cigarette smoking significantly reduces sputum IL-18 levels. This effect is more pronounced in asthmatics than in normal subjects.
McKay
A
A
Division of Immunology, Infection and Inflammation, University of Glasgow, Glasgow, UK.
Komai-Koma
M
M
MacLeod
K J
KJ
Campbell
C C
CC
Kitson
S M
SM
Chaudhuri
R
R
Thomson
L
L
McSharry
C
C
Liew
F Y
FY
Thomson
N C
NC
D000328:Adult; D001249:Asthma / Q000276:immunology*; D016022:Case-Control Studies; D005260:Female; D006801:Humans; D007150:Immunohistochemistry / Q000379:methods; D020382:Interleukin-18 / Q000032:analysis*; D008297:Male; D008875:Middle Aged; D012907:Smoking / Q000276:immunology*; D013048:Specimen Handling / Q000379:methods; D013183:Sputum / Q000737:chemistry*
D020382:Interleukin-18