Immunization with Attenuated Equine Herpesvirus 1 Strain KyA Induces Innate Immune Responses that Protect Mice from Lethal Challenge. Mus musculus

Equine herpesvirus 1 (EHV-1) is a major pathogen affecting equines worldwide and causes respiratory disease, abortion, and in some cases, neurological disease. EHV-1 strain KyA is attenuated in the mouse and equine, whereas wild-type strain RacL11 induces severe inflammatory infiltration of the lung, causing infected mice to succumb at 4 to 6 days post-infection. Our previous results showed that EHV-1 KyA immunization protected CBA mice from pathogenic RacL11 challenge at 2 and 4 weeks post-immunization, and that the infection with the attenuated KyA elicits protective humoral and cell-mediated immune responses. To investigate the protective mechanisms of EHV-1 KyA by innate immune responses, CBA mice immunized with live KyA were challenged with RacL11 at various times post-vaccination. KyA immunization effectively protected CBA mice from RacL11 challenge at 1 to 7 days post-immunization. Immunized mice lost less than 10% of their preinfection body weight and rapidly regained body weight. Lung virus titers in EHV-1 KyA-immunized CBA mice were 1,000-fold lower at 2 days post-RacL11 challenge than lungs of non-immunized mice, which was indicative of accelerated virus clearance. Affymetrix microarray analysis revealed that IFN-γ and 16 antiviral interferon-stimulated genes (ISGs) were upregulated 3.1- to 48.2-fold at 8 h post-challenge in the lungs of RacL11-challenged mice that had been immunized with KyA. Murine IFN-γinhibited EHV-1 infection of murine alveolar macrophage MH-S cells and effectively protected mice against lethal EHV-1 challenge, suggesting that IFN-γ expression may be important in mediating protection elicited by KyA immunization. These results suggest that EHV-1 KyA can be used as a live attenuated EHV-1 vaccine as well as a prophylactic agent in horses. Overall design: Lungs of CBA mice infected with EHV-1 KyA were harvested at 6 (KyA 6hpi), 8 (KyA 8hpi), and 12 (KyA 12hpi) hours post-infection (hpi). Lungs of CBA mice infected with EHV-1 RacL11 were harvested at 8 hpi (L11 8hpi). CBA mice were immunized with EHV-1 KyA and challenged with RacL11 at 3 days post-immunization. Lungs were harvested at 8 h post-RacL11 challenge (KyA→L11 8hpi). CBA mice were immunized with heat-inactivated KyA (HI-KyA) and challenged with RacL11 at 3 days post-immunization. Lungs were harvested at 8 h post-RacL11 challenge (HI-KyA→L11 8hpi). Affymetrix microarray analyses were performed with infected mice lung RNA. Mock-infected lung RNAs were used as a control.