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Concomitant Inhalation of Cigarette Smoke and Aerosolized Protein Activates Airway Dendritic Cells and Induces Allergic Airway Inflammation in a TLR-Independent Way¹

Lander J. Robays^2,*,, Ellen A. Lanckacker^2,*, Katrien B. Moerloose^*, Tania Maes^*, Ken R. Bracke^*, Guy G. Brusselle^*, Guy F. Joos^* and Karim Y. Vermaelen^3,*

^* Department of Respiratory Medicine, Ghent University Hospital, Ghent, Belgium; and Laboratory of Molecular and Cellular Therapy, Department of Physiology and Immunology, Medical School, Vrije Universiteit Brussel, Belgium

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.

The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

¹ This work was supported by grants from Concerted Research Initiative Ghent University (BOF/GOA 12050698 and BOF/GOA 12.515.04), Interuniversity Attraction Poles Program (Belgian State, Belgian Science Policy, Project P6/35), and FWO Flanders (Project 3G.0052.06). K.R.B. is a postdoctoral fellow of the Fund for Scientific Research Flanders (Fonds voor Wefenschappelijk Onderzoek Vlaanderen).

² L.J.R. and E.A.L. contributed equally to this manuscript.

³ Address correspondence and reprint request to Dr. Karim Vermaelen, Department of Respiratory Medicine, Ghent University Hospital, De Pintelaan 185, 9000 Ghent, Belgium. E-mail address: karim.vermaelen{at}ugent.be

⁴ Abbreviations used in this paper: LN, lymph node; DC, dendritic cell; AW-DC, airway-derived DC; BAL, bronchoalveolar lavage; pDC, plasmacytoid DC; TSLP, thymic stromal lymphopoietin; MHCII, MHC class II; PAS, periodic acid-Schiff; MFI, mean fluorescence intensity; PDL, programmed death ligand.