Immunohistofluorescence studies show up-regulation of ANG in microvascular endothelial layers, co-localized with SFG rickettsiae in lesions, in mouse brains, livers, and lungs on days 3 and 5 post-infection. Dual immunofluorescence staining of SFG rickettsiae (red) and ANG (green) in mouse tissues using a dual wave length filter system revealed that the ANG signal was restricted to microvascular endothelial layers in multiple organs or hepatocytes (green signals in images A-F). First appearing day 3 post-infection, compared to mock controls, R. conorii infection (2 × 105 PFU, red signal) resulted in increased signal of ANG (green signals in image G-L) in the microvascular endothelial layers in brain, liver and lung. Up-regulated ANG is co-localized with R. conorii (red signal) in lesions on day 5 post-infection (image J-L). Nuclei of mouse cells are counter-stained with DAPI (blue).