RT Journal Article SR Electronic T1 Legionella pneumophila-derived outer membrane vesicles promote bacterial replication in macrophages JF European Respiratory Journal JO Eur Respir J FD European Respiratory Society SP PA4648 DO 10.1183/13993003.congress-2016.PA4648 VO 48 IS suppl 60 A1 Anna Lena Jung A1 Cornelia Stoiber A1 Christina Herkt A1 Christine Schulz A1 Wilhelm Bertrams A1 Bernd Schmeck YR 2016 UL http://erj.ersjournals.com/content/48/suppl_60/PA4648.abstract AB Legionella pneumophila, a causative agent of severe pneumonia, primarily infects and replicates within macrophages. We and others have shown that they release outer membrane vesicles (OMVs).Here, we analyzed the influence of L. pneumophila OMVs on macrophages. Differentiated THP-1 cells were incubated with increasing doses of Legionella OMVs, leading to a TLR2-dependent classical activation of macrophages with the release of pro-inflammatory cytokines. Inhibition of NF-κB signaling reduced the induction pro-inflammatory cytokines. Furthermore, treatment of THP-1 cells with OMVs prior to infection reduced replication of L. pneumophila in THP-1 cells. Blocking of TLR2 activation or heat denaturation of OMVs restored bacterial replication in the first 24 h of infection. With prolonged infection-time, OMV pre-treated macrophages became more permissive for bacterial replication than untreated cells, dependent on NF-κB signaling, and showed increased numbers of Legionella-containing vacuoles and reduced pro-inflammatory cytokine induction. Additionally, miRNA-146a was found to be transcriptionally induced by OMVs and to facilitate bacterial replication. Accordingly, IRAK-1, one of miRNA-146a's targets, showed prolonged activation-dependent degradation, which rendered THP-1 cells more permissive for Legionella replication.In conclusion, L. pneumophila OMVs are initially potent pro-inflammatory stimulators of macrophages, acting via TLRs, IRAK-1, and NF-κB, while at later time points, OMVs facilitate L. pneumophila replication by miR-146a-dependent IRAK-1 suppression. OMVs might thereby promote spreading of L. pneumophila in the host.