FIG. 6.

Immunohistochemical localization of E. chaffeensis. Paraffin sections of liver (a) and spleen (b) tissues from C.B-17-scid/bg mice (day 17 postinfection) were stained with biotinylated human anti-E. chaffeensis serum followed by alkaline phosphatase-conjugated streptavidin, developed with Fast Red TR/napthol AS-MX, and counterstained with hematoxylin (seen as brown to blue staining). The intense red coloration indicates the presence of E. chaffeensis morulae. No staining was observed with biotinylated normal human serum and secondary antibodies, and very similar results were obtained with C.B-17-scid mice. Magnification, ×400.