Immunization with Attenuated Equine Herpesvirus 1 StrainKyA InducesInnate Immune Responses that Protect Mice from Lethal Challenge

Equine herpesvirus 1 (EHV-1) is a major pathogen affecting equines worldwide and causes respiratory disease, abortion, and in some cases, neurological disease.EHV-1strain KyA is attenuated in the mouse and equine, whereaswild-typestrain 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 theattenuatedKyA 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 timespost-vaccination. KyA immunization effectively protected CBA mice from RacL11 challenge at 1 to 7 dayspost-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 thatIFN-and16 antiviral interferon-stimulated genes (ISGs) were upregulated 3.1- to 48.2-fold at 8 h post-challengein the lungs of RacL11-challenged mice that had been immunized with KyA. Murine IFN-inhibitedEHV-1 infection of murine alveolar macrophage MH-S cells andeffectively protected mice against lethal EHV-1 challenge, suggesting that IFN-expression may be important in mediating protection elicited by KyA immunization. These results suggestthat EHV-1 KyA can be used asa live attenuated EHV-1 vaccine as well as a prophylactic agent in horses.

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Kim SK, Shakya AK, O'Callaghan DJ