Equine herpesvirus type 1 pUL56 modulates innate responses of airway epithelial cells

Recently, the product of equine herpesvirus type 1 (EHV-1) ORF1, a homolog to HSV-1 pUL56, was shown to modulate MHC-I expression and innate immunity. Here, we investigated modulation of respiratory epithelial immunity by EHV-1 pUL56 and compared responses to those of PBMCs, which are important target cells that allow cell-associated EHV-1 viremia. The salient observations are as follows: (i) EHV-1 significantly down-modulated MHC-I and MHC-II expression in equine respiratory epithelial cells (ERECs). MHC-I expression remained unaffected in PBMCs and MHC-II expression was increased. (ii) Infection with an EHV-1 ORF1 deletion mutant partially restored MHC-I and MHC-II expression and altered IFN-alpha and IL-10 mRNA expression. (iii) Deletion of EHV-1 ORF1 also significantly increased chemokine expression and chemotaxis of monocytes and neutrophils in ERECs. Collectively, these results suggest a role for EHV-1 pUL56 in modulation of antigen presentation, cytokine expression and chemotaxis at the respiratory epithelium, but not in PBMC.