Active Aβ vaccination in APPSw/NOS2-/- mice activates the MMP9 system. Panel A shows the average (± SEM) fold change for components of the MMP9 system in mice vaccinated with either KLH or Aβ for 4 months. MMP3 and MMP9 are significantly increased. The dashed line indicates the average gene expression of the non-transgenic control mice. ** indicates P < 0.01 compared to KLH vaccinated APPSw/NOS2-/- mice. Panel B shows the average (± SEM) protein levels of MMP3, MMP9 and TIMP1 as measured by sandwich ELISA. Data are normalized to the protein concentration of the tissue homogenate. ** indicates P < 0.01 compared to KLH vaccinated APPSw/NOS2-/- mice.