Two-dimensional gel electrophoresis analysis in simultaneous influenza pneumonia and bacterial infection in mice

Severe pneumonia is found in simultaneous influenza pneumonia and bacterial infection, and suggests a relationship with immunological mechanisms. Here, we performed two-dimensional gel electrophoresis to detect immunological molecules related to the fulminant pneumonia caused by influenza virus and Streptococcus pneumoniae co-infection in mice. We found two spots that were expressed strongly in co-infected mouse lungs, compared with S. pneumoniae or influenza virus singly infected mouse lungs. The spots were analysed by mass spectrometry, and identified as alpha-1 anti-trypsin (A1AT), known as an anti-protease for neutrophil-derived proteolytic enzymes, and creatine kinase, which reflects a greater degree of lung damage and cell death. A1AT expression was increased significantly, and proteolytic enzymes from neutrophils, such as neutrophil elastase, myeloperoxidase and lysozyme, were also secreted abundantly in influenza virus and S. pneumoniae co-infected lungs compared with S. pneumoniae or influenza virus singly infected lungs. These data suggest that A1AT may play a central role as a molecule with broad anti-inflammatory properties, and regulation of the neutrophil-mediated severe lung inflammation is important in the pathogenesis of co-infection with influenza virus and bacteria.