We next compared the kinetics of CD8 T cell expansion between Klra8 and BALB/c mice ( Figure 3A ). We observed a significant increase in total CD8 T cells in the spleen at day 4 post-infection in Klra8 mice but only later in BALB/c animals. We investigated whether this accelerated expansion of CD8 T cells was a result of a faster activation of antiviral effector CD8 T cells. We first analyzed total splenic CD8 T cells for the expression of an O-glycosylated, activation-associated isoform of CD43. The 1B11 monoclonal antibody (mAb) specifically recognizes this isoform of CD43 on CD8 T lymphocytes [37] and identifies the subset of effector cells capable of IFN-c production and potent cytolytic activity ex vivo during the acute phase of a variety of viral infections [38] [39] [40] [41] [42] . We observed the appearance of CD43 hi effector CD8 T cells starting at day 4 post-infection in Klra8 mice but only later in BALB/c animals ( Figure 3B ). We then used MHC class I tetramers loaded with a peptide derived from the IE-1 protein of MCMV in order to quantify the subset of antiviral CD8 T cells specific to this epitope ( Figure 3C ). We observed a faster expansion of the anti-IE-1 CD8 T cells in Klra8 mice, similar to what was observed for total or effector CD8 T lymphocytes. Similar results were obtained when analyzing the CD8 T cell response against another viral peptide, derived from protein m164 (unpublished data). Conversely, and in Splenic leukocytes were isolated from Klra8 and BALB/c mice and analyzed for the frequency of pDCs (120G8 þ CD11c int ), CD11b cDCs (120G8 À CD11c hi CD8a À ), and CD8a cDCs (120G8 À CD11c hi CD8a þ ) within the DX5 À and TCRb À population. Numbers in dot plots represent percent pDCs, percent CD11b cDCs, and percent CD8a cDCs within the total splenocyte population for one representative animal from groups of three mice for days 0 and 2 post-MCMV infection. Graphs represent the total numbers (in millions) of pDCs, CD11b cDCs, and CD8a cDCs present in the spleens of Klra8 and BALB/c mice on days 0, 1.5, 2, and 3 post-MCMV infection. Results are expressed as mean 6 SD of three mice per group. One experiment representative of three is shown. *p 0.05; **p 0.01. doi:10.1371/journal.ppat.0030123.g002 accordance with what has been previously reported in C57BL/ 6 mice depleted of NK cells by antibody treatment [43] , we observed accumulation of effector CD8 T cells in BALB/c mice at later time points after challenge.