Smoking decreases the response of human lung macrophages to double-stranded RNA by reducing TLR3 expression

TitleSmoking decreases the response of human lung macrophages to double-stranded RNA by reducing TLR3 expression
Publication TypeJournal Article
Year of Publication2013
AuthorsTodt JC, Freeman CM, Brown JP, Sonstein J, Ames TM, McCubbrey AL, Martinez FJ, Chensue SW, Beck JM, Curtis JL
JournalRespir Res
Volume14
Pagination33
Date Published2013
ISSN1465-993X
KeywordsAdult, Aged, Cell Line, Cells, Cultured, Cohort Studies, Down-Regulation, Female, Humans, Lung, Macrophages, Alveolar, Male, Middle Aged, RNA, Double-Stranded, Smoking, Toll-Like Receptor 3, Young Adult
Abstract

BACKGROUND: Cigarette smoking is associated with increased frequency and duration of viral respiratory infections, but the underlying mechanisms are incompletely defined. We investigated whether smoking reduces expression by human lung macrophages (Mø) of receptors for viral nucleic acids and, if so, the effect on CXCL10 production.

METHODS: We collected alveolar macrophages (AMø) by bronchoalveolar lavage of radiographically-normal lungs of subjects undergoing bronchoscopies for solitary nodules (n = 16) and of volunteers who were current or former smokers (n = 7) or never-smokers (n = 13). We measured expression of mRNA transcripts for viral nucleic acid receptors by real-time PCR in those AMø and in the human Mø cell line THP-1 following phorbol myristate acetate/vitamin D3 differentiation and exposure to cigarette smoke extract, and determined TLR3 protein expression using flow cytometry and immunohistochemistry. We also used flow cytometry to examine TLR3 expression in total lung Mø from subjects undergoing clinically-indicated lung resections (n = 25). Of these, seven had normal FEV1 and FEV1/FVC ratio (three former smokers, four current smokers); the remaining 18 subjects (14 former smokers; four current smokers) had COPD of GOLD stages I-IV. We measured AMø production of CXCL10 in response to stimulation with the dsRNA analogue poly(I:C) using Luminex assay.

RESULTS: Relative to AMø of never-smokers, AMø of smokers demonstrated reduced protein expression of TLR3 and decreased mRNA for TLR3 but not TLR7, TLR8, TLR9, RIG-I, MDA-5 or PKR. Identical changes in TLR3 gene expression were induced in differentiated THP-1 cells exposed to cigarette smoke-extract in vitro for 4 hours. Among total lung Mø, the percentage of TLR3-positive cells correlated inversely with active smoking but not with COPD diagnosis, FEV1% predicted, sex, age or pack-years. Compared to AMø of never-smokers, poly(I:C)-stimulated production of CXCL10 was significantly reduced in AMø of smokers.

CONCLUSIONS: Active smoking, independent of COPD stage or smoking duration, reduces both the percent of human lung Mø expressing TLR3, and dsRNA-induced CXCL10 production, without altering other endosomal or cytoplasmic receptors for microbial nucleic acids. This effect provides one possible mechanism for increased frequency and duration of viral lower respiratory tract infections in smokers.

TRIAL REGISTRATION: ClinicalTrials.gov NCT00281190, NCT00281203 and NCT00281229.

DOI10.1186/1465-9921-14-33
Alternate JournalRespir. Res.
PubMed ID23497334
PubMed Central IDPMC3599854
Grant ListN01 HR046162 / HR / NHLBI NIH HHS / United States
P30 CA46952 / CA / NCI NIH HHS / United States
R01 HL056309 / HL / NHLBI NIH HHS / United States
R01 HL056309 / HL / NHLBI NIH HHS / United States
R01 HL082480 / HL / NHLBI NIH HHS / United States
R01 HL082480 / HL / NHLBI NIH HHS / United States
T32 AI007413 / AI / NIAID NIH HHS / United States
U01 HL098961 / HL / NHLBI NIH HHS / United States
U01 HL098961 / HL / NHLBI NIH HHS / United States