Concomitant inhalation of cigarette smoke and aerosolized protein activates airway dendritic cells and induces allergic airway inflammation in a TLR-independent way.

Cigarette smoking is associated with the development of allergic asthma. In mice, exposure to cigarette smoke sensitizes the airways toward coinhaled OVA, leading to OVA-specific allergic inflammation. Pulmonary dendritic cells (DCs) are professional APCs involved in immunosurveillance and implicated in the induction of allergic responses in lung. We investigated the effects of smoking on some of the key features of pulmonary DC biology, including trafficking dynamics and cellular activation status in different lung compartments. We found that cigarette smoke inhalation greatly amplified DC-mediated transport of inhaled Ags to mediastinal lymph nodes, a finding supported by the up-regulation of CCR7 on airway DCs. Pulmonary plasmacytoid DCs, which have been involved in inhalational tolerance, were reduced in number after smoke exposure. In addition, combined exposure to cigarette smoke and OVA aerosol increased surface expression of MHC class II, CD86, and PDL2 on airway DCs, while ICOSL was strongly down-regulated. Although inhaled endotoxins, which are also present in cigarette smoke, have been shown to act as DC activators and Th2-skewing sensitizers, TLR4-deficient and MyD88 knockout mice did not show impaired eosinophilic airway inflammation after concomitant exposure to cigarette smoke and OVA. From these data, we conclude that cigarette smoke activates the pulmonary DC network in a pattern that favors allergic airway sensitization toward coinhaled inert protein. The TLR independency of this phenomenon suggests that alternative immunological adjuvants are present in cigarette smoke.

Cigarette smoke-induced pulmonary inflammation and emphysema are attenuated in CCR6-deficient mice.

Chronic obstructive pulmonary disease (COPD) is mainly caused by cigarette smoking, and is characterized by an increase in inflammatory cells in the airways and pulmonary tissue. The chemokine receptor CCR6 and its ligand MIP-3alpha/CCL20 may be involved in the recruitment of these inflammatory cells. To investigate the role of CCR6 in the pathogenesis of COPD, we analyzed the inflammatory responses of CCR6 knockout (KO) and wild-type mice upon cigarette smoke (CS) exposure. Both subacute and chronic exposure to CS induced an increase in cells of the innate and adaptive immune system in the bronchoalveolar lavage, both in CCR6 KO and wild-type mice. However, the accumulation of dendritic cells, neutrophils, and T lymphocytes, which express CCR6, was significantly attenuated in the CCR6 KO mice, compared with their wild-type littermates. In the lung tissue of CCR6 KO mice, there was an impaired increase in dendritic cells, activated CD8(+) T lymphocytes, and granulocytes. Moreover, this attenuated inflammatory response in CCR6 KO mice offered a partial protection against pulmonary emphysema, which correlated with an impaired production of MMP-12. Importantly, protein levels of MIP-3alpha/CCL20, the only chemokine ligand of the CCR6 receptor, and MCP-1/CCL2 were significantly increased upon CS exposure in wild-type, but not in CCR6 KO mice. In contrast, CCR6 deficiency had no effect on the development of airway wall remodeling upon chronic CS exposure. These results indicate that the interaction of CCR6 with its ligand MIP-3alpha contributes to the pathogenesis of CS-induced pulmonary inflammation and emphysema in this murine model of COPD.

Cigarette smoke exposure facilitates allergic sensitization in mice.

BACKGROUND: Active and passive smoking are considered as risk factors for asthma development. The mechanisms involved are currently unexplained. OBJECTIVE: The aim of this study was to determine if cigarette smoke exposure could facilitate primary allergic sensitization. METHODS: BALB/c mice were exposed to aerosolized ovalbumin (OVA) combined with air or tobacco smoke (4 exposures/day) daily for three weeks. Serology, lung cytopathology, cytokine profiles in bronchoalveolar lavage fluid (BALF) and on mediastinal lymph node cultures as well as lung function tests were performed after the last exposure. The natural history and the immune memory of allergic sensitization were studied with in vivo recall experiments. RESULTS: Exposure to OVA induced a small increase in OVA-specific serum IgE as compared with exposure to PBS (P < 0.05), while no inflammatory reaction was observed in the airways. Exposure to cigarette smoke did not induce IgE, but was characterized by a small but significant neutrophilic inflammatory reaction. Combining OVA with cigarette smoke not only induced a significant increase in OVA-specific IgE but also a distinct eosinophil and goblet cell enriched airway inflammation albeit that airway hyperresponsiveness was not evidenced. FACS analysis showed in these mice increases in dendritic cells (DC) and CD4+ T-lymphocytes along with a marked increase in IL-5 measured in the supernatant of lymph node cell cultures. Immune memory experiments evidenced the transient nature of these phenomena. CONCLUSION: In this study we show that mainstream cigarette smoke temporary disrupts the normal lung homeostatic tolerance to innocuous inhaled allergens, thereby inducing primary allergic sensitization. This is characterized not only by the development of persistent IgE, but also by the emergence of an eosinophil rich pulmonary inflammatory reaction.

Short-term cigarette smoke exposure enhances allergic airway inflammation in mice.

RATIONALE: Epidemiologic studies suggest that tobacco smoke contributes to the prevalence and occurrence of exacerbations in asthma. The effect of active smoking in adolescents with atopy is poorly understood. OBJECTIVES: We developed an experimental model to investigate the influence of smoking on antigen-induced airway inflammation and airway responsiveness in mice that were previously sensitized. METHODS: Ovalbumin (OVA)-sensitized BALB/c mice were exposed to air or mainstream smoke (5 days/week) and to phosphate-buffered saline (PBS) or OVA aerosol (3 times/week) for 2 weeks (n = 8 for each group). RESULTS: Airway responsiveness to intravenously injected carbachol was increased (p < 0.05) in smoke- and OVA-exposed mice compared with all other groups. There was an additive effect of smoke and OVA exposure on total cell numbers, macrophages, and dendritic cells in bronchoalveolar lavage fluid and on CD4+ and CD8+ T lymphocytes and dendritic cells in lung tissue (p < 0.05 compared with mice exposed to smoke and PBS and to mice exposed to air and OVA). Concurrent smoke and OVA exposure augmented OVA-specific IgE in serum compared with air and OVA exposure. In lavage fluid supernatant, eotaxin was increased in air- and OVA-exposed mice. The further increase observed in the group exposed to both OVA and cigarette smoke came close to formal significance (p = 0.06). Thymus- and activation-regulated chemokine was augmented in mice exposed to either smoke or OVA, without additional effect. CONCLUSIONS: Our data indicate that acute concurrent exposure to allergen and mainstream cigarette smoke enhances airway inflammation and airway responsiveness in previously sensitized mice.