Dual Chlamydia pneumoniae labeling and Thioflavin S staining of the temporal cortex from an AD brain .Alzheimer's disease temporal cortex is immunolabeled with a monoclonal anti-C. pneumoniaeantibody (Table 1, #5) followed by staining with Thioflavin S on the same tissue specimen. Panel A shows intracellular and extracellular C. pneumoniaeimmunoreactivity (magenta color). Using a FITC filter, panel B shows both Thioflavin S positive intracellular labeling, presumably NFTs, and extracellular amyloid plaques (yellow fluorescence). Panel C shows the light (panel A) (C. pneumoniae) image overlaid on the fluorescent (panel B) (Thioflavin S) image. Panel D shows merged light and fluorescent images of another region of this temporal cortex illustrating merged chlamydia chromogen immunoreactivity and Thioflavin S amyloid/tau fluorescence. Size bars = 50 μm.