Human respiratory epithelium expresses inducible nitric oxide synthase (iNOS) continuously in vivo, however mechanisms responsible for maintenance of expression are not known. We show that IFN ␥ is sufficient for induction of iNOS in primary human airway epithelial cells (

NO synthase 2 (NOS2) is induced in airway epithelium by influenza virus infection. NOS2 induction late in the course of viral infection may occur in response to IFN-γ, but early in infection gene expression may be induced by the viral replicative intermediate dsRNA through the dsRNA-activated protein kinase (PKR). Since PKR activates signaling pathways important in NOS2 gene induction, we determined whether PKR is a component in the signal transduction pathway leading to NOS2 gene expression after viral infection of airway epithelium. We show that NOS2 gene expression in human airway epithelial cells occurs in response to influenza A virus or synthetic dsRNA. Furthermore, dsRNA leads to rapid activation of PKR, followed by activation of signaling components including NF-κB and IFN regulatory factor 1. NOS2 expression is markedly diminished and IFN regulatory factor 1 and NF-κB activation are substantially impaired in PKR null cells. Strikingly, NOS2 induction in response to LPS is abolished in PKR null cells, confirming a central role for PKR in the general signaling pathway to NOS2.

During embryonic development, the mesenchyme of the lungs, gut, kidneys, and other tissues expresses Trps1, an atypical member of the GATA-type family of transcription factors. Our previous work suggested the possibility that Trps1 acts downstream of bone morphogenic protein 7 (Bmp7), which is essential for normal renal development. To examine the role of Trps1 during early renal development, we generated Trps1-deficient mice and examined their renal histology. Compared with wild-type mice, Trps1-deficient newborn mice had fewer tubules and glomeruli, an expanded renal interstitium, and numerous uninduced metanephric mesenchymal cells, which resulted in fewer nephrons. In wild-type kidneys, Trps1 expression was present in ureteric buds, cap mesenchyme, and renal vesicles, whereas Trps1 was virtually absent in Bmp7-deficient kidneys. Furthermore, Trps1-deficient kidneys had low levels of Pax2 and Wt1, which are markers of condensed mesenchymal cells, suggesting that a lack of Trps1 affects the differentiation of cap mesenchyme to renal vesicles. In cultured metanephric mesenchymal cells, Bmp7 induced Trps1 and E-cadherin and downregulated vimentin. Knockdown of Trps1 with small interference RNA inhibited this Bmp7-induced mesenchymal-to-epithelial transition. Last, whole-mount in situ hybridization of Wnt9b and Wnt4 demonstrated prolonged branching of ureteric buds and sparse cap mesenchyme in the kidneys of Trps1-deficient mice. Taken together, these findings suggest that normal formation of nephrons requires Trps1, which mediates mesenchymal-to-epithelial transition and ureteric bud branching during early renal development.

The innate immunity to viral infections induces a potent antiviral response mediated by interferons (IFN). Although IFN-c is detected during the acute stages of illness in the upper respiratory tract secretions and in the serum of influenza A virus-infected individuals, control of influenza A virus is not dependent upon IFN-c as evidenced by studies using anti-IFN-c Ab and IFN-c -/-mice. Thus, we hypothesized that IFN-c is not critical in host survival because influenza A virus has mechanisms to evade the antiviral activity of IFN-c. To test this, A549 cells, an epithelial cell line derived from lung adenocarcinoma, were infected with influenza virus strain A/Aichi/2/68 (H3N2) (Aichi) and/or stimulated with IFN-c to detect IFN-c-stimulated MHC class II expression. Influenza A virus infection inhibited IFN-c-induced up-regulation of HLA-DRa mRNA and the IFN-c induction of class II transactivator (CIITA), an obligate mediator of MHC class II expression. Nuclear translocation of Stat1a upon IFN-c stimulation was significantly inhibited in influenza A virus-infected cells and this was associated with a decrease in Tyr701 and Ser727 phosphorylation of Stat1a. Thus, influenza A virus subverts antiviral host defense mediated by IFN-c through effects on the intracellular signaling pathways. IntroductionInfluenza A viruses are negative-strand RNA viruses that have a segmented genome with a coding capacity for 11 polypeptides. The virus genome is composed of eight different RNA segments, which are tightly associated with the viral nucleoprotein and polymerases in ribonucleoprotein complexes [1]. Influenza A viruses, causing acute infections, continuously escape from recognition by virus neutralizing Ab as a result of accumulation of mutations in their surface glycoproteins hemagglutinin and neuraminidase (antigenic drift) or by introduction of new subtypes of these glycoproteins (antigenic shift) [2,3]. Recent outbreaks of highly pathogenic avian influenza A virus infections in poultry and in humans have raised concerns that a new influenza pandemic will occur in the near future [4]. Thus, prediction of the severity of continuously emerging human influenza virus strains remains a high public health priority, but it is limited by our incomplete understanding of the molecular determinants of pathogenicity in this disease. Although factors dictating the severity of virus disease are complex, interaction between inherent viral properties and host cellular response ultimately determines disease outcome. The first site of viral contact with the host and main target of infection and inflammation is the airway mucosal epithelium. Epithelial cells at the airway mucosal surface have a variety of inflammatory and immune defense mechanisms to deal with virus, including Eur. J. Immunol. 2008. 38: 1559-1573 Immunity to infection expression of cytokines with chemoattractant and proinflammatory functions [5], intercellular adhesion molecule-1 (ICAM-1) [6], IFN regulatory factor 1 (IRF-1) [7], nitric oxide synthase 2 (NOS2) [8], and MHC ...