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Equine Herpesvirus Type 4 UL56 and UL49.5 Proteins Downregulate Cell Surface Major Histocompatibility Complex Class I Expression Independently of Each Other
Faculty
Veterinary Medicine
Year:
2012
Type of Publication:
Article
Pages:
8059-8071
Authors:
Azab, Walid, Osterrieder, Nikolaus, Said, Abdelrahman, Damiani, Armando
DOI:
10.1128/JVI.00891-12
Journal:
JOURNAL OF VIROLOGY AMER SOC MICROBIOLOGY
Volume:
86
Research Area:
Virology
ISSN
ISI:000306614400031
Keywords :
Equine Herpesvirus Type , UL56 , UL49.5 Proteins
Abstract:
Major histocompatibility complex class I (MHC-I) molecules are critically important in the host defense against various pathogens through presentation of viral peptides to cytotoxic T lymphocytes (CTLs), a process resulting in the destruction of virus-infected cells. Herpesviruses interfere with CTL-mediated elimination of infected cells by various mechanisms, including inhibition of peptide transport and loading, perturbation of MHC-I trafficking, and rerouting and proteolysis of cell surface MHC-I. In this study, we show that equine herpesvirus type 4 (EHV-4) modulates MHC-I cell surface expression through two different mechanisms. First, EHV-4 can lead to a significant downregulation of MHC-I expression at the cell surface through the product of ORFI, a protein expressed with early kinetics from a gene that is homologous to herpes simplex virus 1 UL56. The EHV-4 UL56 protein reduces cell surface MHC-I as early as 4 h after infection. Second, EHV-4 can interfere with MHC-I antigen presentation, starting at 6 h after infection, by inhibition of the transporter associated with antigen processing (TAP) through its UL49.5 protein. Although pUL49.5 has no immediate effect on overall surface MHC-I levels in infected cells, it blocks the supply of antigenic peptides to the endoplasmic reticulum (ER) and transport of peptide-loaded MHC-I to the cell surface. Taken together, our results show that EHV-4 encodes at least two viral immune evasion proteins: pUL56 reduces MHC-I molecules on the cell surface at early times after infection, and pUL49.5 interferes with MHC-I antigen presentation by blocking peptide transport in the ER.
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