Modulation of MHC class I expression by African swine fever virus and the role of virus proteins EP153R and CD2v

摘要

Various DNA viruses, including pox- and herpesviruses, express proteins which down-regulate host MHC class I antigen expression as an immune evasion strategy. Previous studies into whether ASFV modulates expression of the porcine MHC class I molecule, SLA I, have not provided a clear answer. In this thesis, the effect of African swine fever virus (ASFV) and the roles of two proteins, EP153R and CD2v, were investigated in the transcription, protein synthesis and expression of SLA-I at the surface of ASFV-infected cells. The expression and localisation of EP153R were also investigated. CD2v has previously been shown to bind mABp1, an actin binding adaptor protein implicated in vesicular transport. Higher expression of surface SLA-I was observed in macrophages infected with virulent isolates of ASFV than in cells infected with their ΔCD2v deletion mutants. Through binding to mABp1, CD2v may indirectly affect transport and cell surface expression of SLA-I. The C-type lectin domain of EP153R shows similarities to that of Clec2B, the ligand of NK cell activating receptor NKp80. Previous studies have suggested that EP153R inhibits up-regulation of SLA-I expression in response to stimulation with cytokines. Results presented here confirmed a reduction in up-regulation of surface SLA-I in porcine kidney cells stimulated with both PMA/ion and IFN-γ when transfected with EP153R from virulent ASFV isolate Benin 97/1, but not ASFV Georgia 2007/1. Localisation and processing studies revealed different patterns of EP153R expression in ASFV-infected and uninfected cells. In uninfected cells, the expressed protein localises to the ER with no surface expression detected. In ASFV-infected cells, both fully modified and deglycosylated forms of the expressed protein are smaller, and it is detected throughout the cytoplasm and at the cell surface. EP153R is probably processed by a virus-encoded/induced enzyme and localisation and processing of the protein may be important for its function(s) during virus infection.