ERVW-1 and viral infectious disease: I-Ab tetramers presenting an immunodominant peptide (aa 641–655) from West Nile Virus (WNV) envelope protein (E641:I-Ab) were used because WNV lethality increases over the lifespan of mice and humans, making it a useful model for investigating age-related defects in susceptibility to viral infection and vaccine efficacy (Brien et al., 2008, 2009; Uhrlaub et al., 2011; Suthar et al., 2013).