Legionella pneumophila induced IL-8 expression in human pulmonary epithelium by MAP kinases, NF-kB and histone modifications

Introduction: L. pneumophila induced severe pneumonia in humans due to the inhalation of Legionella-contaminated water droplets. In this study we tested the hypothesis that Legionella induced pro-inflammatory activation of pulmonary epithelial cells and analyzed involved signalling pathways.

Methods: human lung epithelial cells (A549), Bioplex-assay, IL-8-ELISA, Western blot, reportergen-assay, chromatin-immunoprecipitation (ChIP).

Results: L. pneumophila induced the expression of various chemo- and cytokines in A549 cells and activated MAPK pathways. Inhibition of p38 MAPK reduced the expression of IL-8, which was studied in detail as a model cytokine. In contrast, blocking of p42/44 ERK or JNK kinase had no effect on IL-8 secretion in Legionella infected A549 cells. Legionella stimulated NF-kB transcription factor dependent expression of IL-8. ChIP experiments with Legionella infected cells demonstrated increased acetylation and phosphorylation of histone H3 and H4, which was accompanied by recruitment of NF-kB-RelA as well as RNA-polymerase II to the IL-8 promotor. Moreover, inhibition of histone-deacetylases increased Legionella-related NF-kB-dependent gene transcription and cytokine release in A549 cells.

In conclusion, Legionella induced prominent proinflammatory gene transciption in A549 cells. Legionella related IL-8 expression depended on the activation of p38 MAPK and NF-kB as well as histone modifications.

The German Federal Ministry of Education and Research, Competence Network CAPNETZ supported this study.