RSV Antigens are detected in Peripheral Blood Monocytes by Immunohistochemical (IHC) staining. Peripheral blood was collected in RSV-infected mice (n = 8) and non-infected controls (n = 6) from two independent experiments on day 5 post inoculation. Four-micron sections were IHC stained for RSV with a polyclonal antibody. Fig. 3A-C demonstrates peripheral blood monocytes with positive staining for RSV in the cytoplasm. Uninfected mice did not demonstrate any positive staining (Fig 3D).