Figure 4. Results of testing for Nipah virus (NiV) in spleen tissue from representative vaccinated African green monkeys (Chlorocebus aethiops). A, C, E, G) Hematoxylin and eosin staining; B, D, F, H) immunohistochemistry of tissues labeled with NiV N protein–specific polyclonal rabbit antibody. In stained tissue from the control animal (A), moderate necrosis and drop out of the white pulp (*), with hemorrhage, and fibrin within germinal centers are seen; stained sections examined from the NiV F (C), NiV G (E), and NiV F/G (G) groups were devoid of any significant lesions compared with sections from the control animal. In antibody-labeled tissues from the control animal (B), strong immunolabeling for NiV antigen with scattered mononuclear cells (white arrow) and syncytial cells within germinal centers were found, and the endothelium of small caliber vessels had strong cytoplasmic immunolabeling for NiV antigen; no immunolabeling for NiV antigen was identified from the NiV F (D), NiV G (F), and NiV F/G (H) groups. Original magnification ×20.