The Journal of Immunology Dual TCR Expression Biases Lung Inflammation in DO11.10 Transgenic Mice and Promotes Neutrophilia via Microbiota-Induced Th17 Differentiation Muriel M. Lemaire,* ,† Laure Dumoutier,* ,† Guy Warnier,* Catherine Uyttenhove,* Jacques Van Snick,* ,† Magali de Heusch,* ,† Monique Stevens,* and Jean-Christophe Renauld* ,† A commonly used mouse model of asthma is based on i.p. sensitization to OVA together with aluminum hydroxide (alum). In wild- type BALB/c mice, subsequent aerosol challenge using this protein generates an eosinophilic inflammation associated with Th2 cytokine expression. By constrast, in DO11.10 mice, which are transgenic for an OVA-specific TCR, the same treatment fails to induce eosinophilia, but instead promotes lung neutrophilia. In this study, we show that this neutrophilic infiltration results from increased IL-17A and IL-17F production, whereas the eosinophilic response could be restored upon blockade of IFN-g, indepen- dently of the Th17 response. In addition, we identified a CD4 + cell population specifically present in DO11.10 mice that mediates the same inflammatory response upon transfer into RAG2 2/2 mice. This population contained a significant proportion of cells expressing an additional endogenous TCR a-chain and was not present in RAG2 2/2 DO11.10 mice, suggesting dual antigenic specificities. This particular cell population expressed markers of memory cells, secreted high levels of IL-17A, and other cytokines after short-term restimulation in vitro, and triggered a neutrophilic response in vivo upon OVA aerosol challenge. The relative numbers of these dual TCR lymphocytes increased with the age of the animals, and IL-17 production was abolished if mice were treated with large-spectrum antibiotics, suggesting that their differentiation depends on foreign Ags provided by gut microflora. Taken together, our data indicate that dual TCR expression biases the OVA-specific response in DO11.10 mice by inhibiting eosinophilic responses via IFN-g and promoting a neutrophilic inflammation via microbiota-induced Th17 differ- entiation. The Journal of Immunology, 2011, 187: 3530–3537. A llergic asthma is a frequent pulmonary disorder caused by dysregulated immune responses that are triggered by inhaled environmental Ags. This chronic disease is characterized by lung inflammation, mucus accumulation, and airway hyperresponsiveness, and leads to tissue remodeling (1, 2). The pathogenic role of CD4 + Th2 cells has been well documented throughout mouse preclinical models (3). Following the Th1/Th2 general paradigm, Th1-derived IFN-g is supposed to antagonize Th2 differentiation, and, conversely, Th2-derived IL-4 inhibits the Th1 axis. Hence, it has been suggested that asthma could develop as a result of an impaired balance of Th1 in favor of Th2. Yet, this dichotomic model has been challenged by the discovery of the Th17 subset, which plays a key role in antibacterial defenses and autoimmunity, but also soon became implicated in asthma (4, 5). An increase of IL-17 production has been observed in airways and plasma from asthmatic patients (6, 7), and the level of this cyto- kine in the sputum has been correlated with the severity of bronchial hyperreactivity (8). In addition, the expression level of RORgt, the key transcriptional factor for Th17 differentiation, was augmented in asthmatic patients (7). In mouse models, accumu- lating evidence supports a key role for IL-17 induction in lung inflammation triggered by sensitization and challenge with aller- gens (9–11). Whereas IL-5–producing Th2 cells are required for lung eosinophilia, IL-17 was shown to be responsible for neu- trophil recruitment to the lungs following local Ag stimulation, as this influx was blocked either by anti–IL-17 Ab administration (9, 12) or in IL-17R 2/2 mice (11). In line with these observations, in vitro differentiated Th17 cells specific for OVAwere shown to induce airway neutrophilic inflammation in adoptively transferred wild-type mice after local OVA challenge (13, 14). Whether Th17 cells influence Th2 lung inflammation remains a controversial issue. In a classical model elicited by i.p. sensiti- zation and aerosol challenge with OVA, it has been reported that IL-17 inhibition could diminish lung neutrophilia and increase eosinophilia (12). Conversely, in a similar model, but with epi- cutaneous sensitization, the lung eosinophilic response was ab- rogated in favor of an elevated neutrophil infiltration when mice were deficient in both IL-4 and IL-13 (15). These results suggest that Th17 and Th2 cells are able to antagonize each other during allergen-induced airway inflammation. However, other results also support a synergy between the Th2 and Th17 axes. Using the same OVA sensitization and challenge protocol, one group has shown that anti–IL-17 Abs inhibited not only lung neutrophilia, but also eosinophilia, and decreased Th2 cytokine levels in bron- choalveolar lavage (BAL) fluid (16). Following OVA inhalation, it has also been reported that recipient mice transferred with in vitro differentiated OVA-specific Th cells presented an increase of BAL neutrophil, but also of eosinophil numbers when Th17 cells were injected concomitantly to Th2 cells. Moreover, airway *Ludwig Institute for Cancer Research, Brussels Branch, B-1200 Brussels, Belgium; and † de Duve Institute, Universite ´ Catholique de Louvain, B-1200 Brussels, Belgium Received for publication June 9, 2011. Accepted for publication July 24, 2011. This work was supported in part by Fonds pour la Formation et la Recherche dans l’Industrie et dans l’Agriculture (Brussels, Belgium), the Belgian Programme on Interuniversity Poles of Attraction initiated by the Belgian State, Prime Minister’s Office, Science Policy Programming, and the Actions de Recherche Concerte ´es of the Communaute ´ Franc ¸aise de Belgique. L.D. is a research associate of the Fonds Na- tional de la Recherche Scientifique. Address correspondence and reprint requests to Dr. Jean-Christophe Renauld, Lud- wig Institute for Cancer Research and Experimental Medicine Unit, Universite ´ Cath- olique de Louvain, Avenue Hippocrate 74, B-1200 Brussels, Belgium. E-mail address: renauld@bru.licr.org Abbreviation used in this article: BAL, bronchoalveolar lavage. Copyright Ó 2011 by The American Association of Immunologists, Inc. 0022-1767/11/$16.00 www.jimmunol.org/cgi/doi/10.4049/jimmunol.1101720