BioProject

Peumonia is the most common cause of death due to infectious diseases in the western hemisphere. The molecular events associated with pulmonary infections caused by Streptococcus pneumoniae and Influenza A virus are incompletely understood. Pathophysiological and protective processes are initiated by immune receptors specifically recognizing pathogenic structures serving to elicit a qualitatively and quantitatively adequate immune response. To provide a molecular framework towards a better understanding of the processes relevant in severe infectious pneumonia we performed a transcriptome analysis of lungs from mice infected with S. pneumoniae or Influenza A virus. Overall, we detected 1300 genes that exhibit significant differential expression after infection with either pathogen. Of those were approximately 36 % specific for pneumococcal and 30 % specific for the viral infection, yielding pathogen-specific as well as common inflammatory transcriptional signatures. Characteristically, these results resolve not only a differential response on the cytokine and chemokine level, although common induction of type I and type II interferons, TNFa, and IL-6 underlies both infections, but emphasize the potentially important role exerted by many genes implicated in the regulation and fine tuning of the inflammatory response. Furthermore, we noted a specific decrease in B cells after S. pneumoniae infection, which is not solely confined to the lung. Massive induction of apoptosis in pulmonary B cells could reflect a pneumococcal virulence strategy aiming against the lymphocyte population that is of utmost importance for the defence against capsulated bacteria. The pathophysiological consequences of Influenza A virus infection become obvious through differential induction of genes implicated in tissue regeneration and proliferation associated with detection of the emerging protective T cell response. These results may provide new insights into the pathogenesis and protective mechanisms important for the development of improved diagnostic and therapeutic strategies. Keywords: pathogen comparison, time course Overall design: Microarray analyses were performed as two-colour hybridizations. RNA was labelled with a Fluorescent Linear Amplification Kit (Agilent Technologies). Briefly, 4 µg total RNA was reverse transcribed with an oligo-dT-T7 promoter primer and MMLV-RT. Second strand synthesis was carried out with random hexamers. Fluorescent antisense cRNA was synthesized with either cyanine 3-CTP (Cy3-CTP) or cyanine 5-CTP (Cy5-CTP) and T7 polymerase. Purified products were quantified at A552nm for Cy3-CTP and A650nm for Cy5-CTP. Prior hybridization, 1.25 µg labelled cRNA each were fragmented, mixed with control targets and hybridization buffer according to the supplier's protocol (Agilent Technologies). Hybridizations were performed for 17 h at 60°C. The slides were washed according to the manufacturer's protocol and scanning of the arrays was performed with 5 µm resolution using a DNA microarray laser scanner (Agilent Technologies). To compensate for dye specific effects, and to ensure validity of the data, a colour swap analysis (fluorescence reversal) was performed. Features were extracted with the image analysis tool Version A6.1.1.1 from Agilent Technologies. Subsequent data analyses were carried out on the Rosetta Inpharmatics platform Resolver Built 3.2.2. Differential expression patterns were identified by applying 2-fold expression level cut-offs and an anti-correlation of the dye reversal experiments with an error weighted p-value < 0.05.