Legionella pneumophila-induced IκBζ-dependent expression of interleukin-6 in lung epithelium.

Severe community- and hospital-acquired pneumonia is caused by Legionella pneumophila. Lung airway and alveolar epithelial cells comprise an important sentinel system in airborne infections. Although interleukin (IL)-6 is known as a central regulator of the immune response in pneumonia, its regulation in the lung is widely unknown. Herein, we demonstrate that different L. pneumophila strains induce delayed expression of IL-6 in comparison with IL-8 by human lung epithelial cells. IL-6 expression depended, at early time points, on flagellin recognition by Toll-like receptor (TLR)5, activity of mitogen-activated protein kinase/extracellular signal-regulated kinase kinase (MEK)1 and p38 mitogen-activated protein (MAP) kinase, and, at later time points, on the type-IV secretion system. In the same manner, but more rapidly, the recently described transcription factor IκBζ was induced by Legionella infection and, binding to the nuclear factor (NF)-κB subunit p50 - recruited to the il6 promoter together with CCAAT-enhancer-binding protein ß and phosphorylated activator protein-1 subunit cJun. Similarly, histone modifications and NF-κB subunit p65/RelA appeared at the iκbζ and subsequently at the il6 gene promoter, thereby initiating gene expression. Gene silencing of IκBζ reduced Legionella-related IL-6 expression by 41%. Overall, these data indicate a sequence of flagellin/TLR5- and type IV-dependent IκBζ expression, recruitment of IκBζ/p50 to the il6 promoter, chromatin remodelling and subsequent IL-6 transcription in L. pneumophila-infected lung epithelial cells.

Porphyromonas gingivalis dihydroceramides induce apoptosis in endothelial cells.

Porphyromonas gingivalis dihydroceramides are found in extracts of calculus-contaminated root surfaces, diseased gingival tissue, and atherosclerotic plaques. These ceramides have been shown to promote inflammatory secretory responses in gingival fibroblasts. Little is known about their effects on the vascular system. We tested the hypothesis that P. gingivalis lipids induce apoptosis of human endothelial cells, and investigated the effects of extracted and purified P. gingivalis lipids on human umbilical vein endothelial cells. P. gingivalis phosphoglycerol dihydroceramides induced apoptosis, but not necrosis, in endothelial cells. Early apoptotic cells showed exposure of phosphatidylserine on the cell surface, followed by the cleavage of procaspases 3, 6, and 9. The release of apoptosis-inducing factor was increased, suggesting mitochondrial involvement. Different caspase inhibitors and cAMP elevation blocked DNA fragmentation. Moreover, N-acetylcysteine significantly reduced apoptosis, suggesting a role for reactive oxygen species in this process. Analysis of these data indicates that dihydroceramides may be important virulence factors of P. gingivalis.

Moraxella catarrhalis induces ERK- and NF-kappaB-dependent COX-2 and prostaglandin E2 in lung epithelium.

Moraxella catarrhalis is a major cause of infectious exacerbations of chronic obstructive lung disease. Cyclooxygenase (COX)-derived prostaglandins, such as prostaglandin E(2) (PGE(2)), are considered to be important regulators of lung function. The present authors tested the hypothesis that M. catarrhalis induces COX-2-dependent PGE(2) production in pulmonary epithelial cells. In the present study, the authors demonstrate that M. catarrhalis specifically induces COX-2 expression and subsequent PGE(2) release in pulmonary epithelial cells. Furthermore, the prostanoid receptor subtypes EP2 and EP4 were also upregulated in these cells. The M. catarrhalis-specific ubiquitous cell surface protein A1 was important for the induction of COX-2 and PGE(2). Moreover, M. catarrhalis-induced COX-2 and PGE(2) expression was dependent on extracellular signal-regulated kinase 1/2-driven activation of nuclear factor-kappaB, but not on the activation of p38 mitogen-activated protein kinase. In conclusion, the present data suggest that ubiquitous cell surface protein A1 of Moraxella catarrhalis, extracellular signal-regulated kinase 1/2 and nuclear factor-kappaB control cyclooxygenase-2 expression and subsequent prostaglandin E(2) release by lung epithelial cells. Moraxella catarrhalis-induced prostaglandin E(2) expression might counteract lung inflammation promoting colonisation of the respiratory tract in chronic obstructive pulmonary disease patients.

Legionella pneumophila-induced NF-kappaB- and MAPK-dependent cytokine release by lung epithelial cells.

Legionella pneumophila causes community-acquired pneumonia with high mortality, but little is known about its interaction with the alveolar epithelium. The aim of this study was to investigate whether L. pneumophila infection of lung epithelial cells (A549) resulted in pro-inflammatory activation. L. pneumophila infection induced liberation of interleukin (IL)-2, -4, -6, -8 and -17, monocyte chemoattractant protein-1, tumour necrosis factor-alpha, IL-1beta, interferon-gamma and granulocyte colony-stimulating factor, but not of IL-5, -7, -10, -12 (p70) or -13 or granulocyte-macrophage colony-stimulating factor. The present study focused on IL-8 and found induction by L. pneumophila strains 130b, Philadelphia 1, Corby and, to a lesser extent, JR32. Knockout of dotA, a central gene involved in type IVB secretion, did not alter IL-8 induction, whereas lack of flagellin significantly reduced IL-8 release by Legionella. Moreover, p38 mitogen-activated protein kinase (MAPK) was activated and kinase inhibition reduced secretion of induced cytokines, with the exception of IL-2 and granulocyte colony-stimulating factor. In contrast, inhibition of the MAPK kinase 1/extracellular signal-regulated kinase pathway only reduced the expression of a few cytokines. L. pneumophila also induced binding of nuclear factor-kappaB subunit RelA/p65 and RNA polymerase II to the il8 promoter, and a specific inhibitor of the inhibitor of nuclear factor-kappaB complex dose-dependently lowered IL-8 expression. Taken together, Legionella pneumophila activated p38 mitogen-activated protein kinase- and nuclear factor-kappaB/RelA pathway-dependent expression of a complex pattern of cytokines by human alveolar epithelial cells, presumably contributing to the immune response in legionellosis.