Poster Presentation 23rd Annual Lorne Proteomics Symposium 2018

A blockage, a trickle or a deluge? TAP’ing into viral immune evasion (#102)

Nathan P Croft 1 , Thilaga Velusamy 2 , Stewart Smith 2 , Anthony W Purcell 1 , David C Tscharke 2
  1. Infection and Immunity Program & Department of Biochemistry and Molecular Biology, Biomedicine Discovery Institute, Monash University, Clayton, VIC, Australia
  2. John Curtin School of Medical Research, The Australian National University, Canberra, ACT, Australia

ICP47 is an iconic immune modulator encoded by herpes simplex virus (HSV) that hides infected cells from the immune system by inhibiting the presentation of peptides to CD8 T cells. Specifically, ICP47 functions by binding to the transporter associated with antigen presentation (TAP), blocking peptide transport and loading onto MHCI, thus reducing peptide display at the cell surface. During its identification in the 1990s, ICP47 was attributed to have near-absolute species bias for human TAP; however, later work showed that ICP47 can contribute to HSV neurovirulence in mice. Given the continued use of mouse models as a mainstay of HSV research in vivo, we re-examined this controversy using a new set of ICP47 null viruses through a combination of infection models and epitope identification and quantification by mass spectrometry. In a mouse flank infection model, deletion of ICP47 did not alter lesion development or virus load, latency, spread and reactivation. By contrast, we show ICP47 does inhibit antigen presentation significantly on HSV-infected mouse cells using in vitro antigen presentation assays. Further, we identified more HSV-derived peptides on ICP47-deficient cells than wild-type and subsequently quantified peptide presentation of 13 such epitopes and the impact of ICP47 in cells expressing either mouse or human TAP molecules. These data confirm that ICP47 almost entirely blocks human TAP-mediated peptide presentation, though the degree of inhibit was somewhat peptide-specific; conversely, the effect of ICP47 on mouse TAP was far less profound, resulting in a two- to five-fold reduction in MHC-peptide abundance. These data allow us to put the first numbers on viral immune evasion at the MHC-peptide level and validate the species-specific nature of ICP47. Thus, despite reduced, though nonetheless significant, antigen presentation in mouse cells, ICP47 is not an effective immune modulator in mice where HSV is confined to the peripheral nervous system.