CD4 and infection: Congenic recipients (Thy1.1) were infected with MCMV-BAC or MCMV-B5 or uninfected, and CTV-labelled CD4-purified B5 TCR Tg T cells were adoptively transferred for the last five days of infection, testing presentation of B5 peptide between days 5–10, 25–30, or 55–60 of MCMV infection.