Chlamydia pneumoniae immunoreactivity in AD brain tissue. Alzheimer's disease brain cerebral cortex immunolabeled with a mouse anti-C. pneumoniaemonoclonal antibody (Table 1, #5) demonstrates both intracellular and extracellular immunolabeling as indicated by the magenta color. Panel A illustrates the temporal cortex labeled with no primary antibody and both anti- mouse HRP and anti-mouse AP conjugated secondary antibodies reacted with both DAB and AP red. Panel B illustrates an extracellular labeling pattern and panels C and D illustrate cellular labeling in the frontal cortex. Areas delineated by the boxes are higher magnification images of the immunoreactivity in panels B-D. Size bar = 50 μm.