IL-10-/- efficiently clear LCMVARM but upon infection with LCMVClone13 these mice exhibit an early enhanced T cell response, followed by anergy and viral persistence. a) IL-10-/- (open bars) or control wild type (WT) C57BL/6 (filled bars) mice were infected with LCMVARM and 8 days later the CD8 T cells were assayed for their ability to produce IFN-γ upon stimulation with LCMV peptides, GP33 and NP396. The frequencies ( ± standard deviation) of IFN-g+ CD8+ T cells for the two groups of mice are shown; there was no significant difference between the groups. b) IL-10-/- mice clear LCMVARM as efficiently as C57BL/6 mice. Groups of mice were infected with 2 × 105 pfu LCMVARM and eight days post infection, the sera from IL-10-/- (open circles) and WT, C57BL/6 (filled circles) mice were assayed for infectious virus by plaque assay. c) Cohorts of C57BL/6 (IL-10+/+), IL-10+/- and IL-10-/- mice were infected with LCMVClone13 and 8 or 30 days later, the ability of CD8 T cells to produce IFN-g upon stimulation with LCMV peptides, GP33 (filled bars) and NP396 (open bars) were assayed by intracellular cytokine staining. The absolute numbers of splenic IFN-γ+ CD8+ T cells ( ± SD) for the three groups are plotted. Robust CD8 T cells responses were observed in IL-10-/- mice. For each of the peptide stimulation at day 8, the numbers of IFN-γ+ CD8+ T cells in IL-10-/- were statistically significant than those in IL-10+/- (p < 0.01) and IL-10+/+ (p < 0.001) mice. The numbers of IFN-γ+ CD8 T cells in IL-10+/- and wild type, IL-10+/+ mice were not statistically significant. d) Both IL-10+/+ and IL-10-/- mice remained persistently infected, 30 days after infection with LCMVClone13. Sera from infected, IL-10-/- (open circles) and IL-10+/+ (filled circles) were assayed for virus by plaque assay. The difference in the viral titers between the two groups was not statistically significant. Each dot represents an individual mouse.