FIG 4.

Immunization with KyA is protective against challenge with pathogenic RacL11. (A and B) Rapid virus clearance from the lungs of CBA mice immunized with KyA. Groups of CBA mice (n = 6) were infected intranasally with KyA (2 × 10⁶ PFU/mouse) and were challenged with RacL11 (1.5 × 10⁶ PFU/mouse) at 3 or 7 days postimmunization. On days 1 to 5 postchallenge, the lungs were removed and homogenized, and the amount of infectious EHV-1 was determined by standard plaque titration as described previously (50). KyA, KyA-infected mice; RacL11, RacL11-infected mice. (C) Histological sections of infected mouse lungs. CBA mice were intranasally mock infected or infected with KyA and were challenged with RacL11 at 3 days postimmunization (mock → RacL11 or KyA → RacL11, respectively). On days 4 and 10 p.i., the mice were sacrificed, and the lungs were removed. The lung tissue was mounted and processed for histological evaluation as described in Materials and Methods. The resulting slides were photographed at ×20 magnification with a Nikon TE300 Eclipse microscope. dpi, days postinfection; dpc, days post-RacL11 challenge; B, bronchus. Bronchial epithelial (arrows) and inflammatory infiltration (arrowheads) regions are indicated.