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

Abstract

BackgroundCigarette 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.MethodsWe 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.ResultsRelative 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.ConclusionsActive 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 registrationClinicalTrials.gov NCT00281190, NCT00281203 and NCT00281229.

Cigarette smoke attenuates the RIG-I-initiated innate antiviral response to influenza infection in two murine models

“…In vivo, CS augments the expression and responses of TLR3 in human macrophages (18) and in murine lung tissue. However, two research groups have reported that smoking decreased TLR3 induction in human lung macrophages and NEC (13,33). In our previous study, we also found a modest increase in TLR3 in human lung during IAV infection that was inhibited by CSE (35).…”

At the Checkpoint: Lung CD8+ T Cells, Respiratory Viruses, and Chronic Obstructive Pulmonary Disease

“…After publication of these results, supplemented by a collaborative study of several cohorts indicating that airflow limitation but not CMH was strongly related to mortality (4), research interest in CMH and recurrent respiratory infections diminished for some years, and the main research focus was directed toward studies of airflow limitation. Yet, based on longitudinal observations of cohorts of working men from Paris, Kauffmann and Annesi suggested that presence of mucus hypersecretion was perhaps not as innocent as described by Fletcher and colleagues (5,6). This notion was further supported by Copenhagen studies showing a nontrivial association between CMH and FEV 1 decline and death from obstructive lung disease (7)(8)(9).…”

“…Nonetheless, could acquired (or perhaps minor genetic) defects in mucosal immunity also make patients with COPD simply less able to eliminate incipient VLRTIs? Smoking definitely decimates lung innate immune defenses (5), including antiviral recognition (6). Yet COPD can clearly progress, despite decades of smoking cessation.…”

MicroRNA-34a Negatively Regulates Efferocytosis by Tissue Macrophages in Part via SIRT1

“…Clinical characteristics of the human volunteers are shown in Table 1. Subjects underwent bronchoscopy under moderate conscious sedation using a fiberoptic bronchoscope and resident human AMø were isolated by segmental bronchoalveolar lavage, both as recently described in detail (41). Not all subjects were used in every experiment.…”