To confirm the mechanistic role of MCMV.env-induced CD4+ T cells in providing help for the induction of potent antibody responses upon FV challenge infection, we compared the levels of neutralizing antibodies in MCMV.env immunized mice that were challenged with FV without further intervention, or after depletion of CD4+ cells, and found significantly reduced levels of neutralizing antibodies on day 10 after FV infection in mice depleted of CD4+ cells compared to MCMV.env immunized mice (Fig 9E). The gene discussed is CD4; the disease is infection.