Here, we investigated the role of IL-27 upon infection with MCMV, a persistent/latent virus, and similar to our previous results with the persistent systemically replicating virus; LCMV Cl13 [27], found that IL-27 positively regulated the numbers of antiviral CD4 T cells, as noted by reduced numbers of polyclonal CD11a+CD49d+ and M09133-147 specific CD4 T cells in Il27ra-/- mice. The gene discussed is CD4; the disease is infection.