• Eric Bernasconi, Céline Pattaroni, Angela Koutsokera, Christophe Pison, Romain Kessler, Christian Benden, Paola M Soccal, Antoine Magnan, John-David Aubert, Benjamin J Marsland, Laurent P Nicod, and SysCLAD Consortium.
• 1 Service de Pneumologie, Centre Hospitalier Universitaire Vaudois and Swiss Transplant Cohort Study, Lausanne, Switzerland.
• Am. J. Respir. Crit. Care Med. 2016 Nov 15; 194 (10): 1252-1263.

RationaleIn lung transplant recipients, long-term graft survival relies on the control of inflammation and tissue remodeling to maintain graft functionality and avoid chronic lung allograft dysfunction. Although advances in clinical practice have improved transplant success, the mechanisms by which the balance between inflammation and remodeling is maintained are largely unknown.ObjectivesTo assess whether host-microbe interactions in the transplanted lung determine the immunologic tone of the airways, and consequently could impact graft survival.MethodsMicrobiota DNA and host total RNA were isolated from 203 bronchoalveolar lavages obtained from 112 patients post-lung transplantation. Microbiota composition was determined using 16S ribosomal RNA analysis, and expression of a set of genes involved in prototypic macrophage functions was quantified using real-time quantitative polymerase chain reaction.Measurements And Main ResultsWe show that the characteristics of the pulmonary microbiota aligned with distinct innate cell gene expression profiles. Although a nonpolarized activation was associated with bacterial communities consisting of a balance between proinflammatory (e.g., Staphylococcus and Pseudomonas) and low stimulatory (e.g., Prevotella and Streptococcus) bacteria, "inflammatory" and "remodeling" profiles were linked to bacterial dysbiosis. Mechanistic assays provided direct evidence that bacterial dysbiosis could lead to inflammatory or remodeling profiles in macrophages, whereas a balanced microbial community maintained homeostasis.ConclusionsThe crosstalk between bacterial communities and innate immune cells potentially determines the function of the transplanted lung offering novel pathways for intervention strategies.

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