B7-H1 negatively regulates CD4 T cell activity in the central nervous system. (A) Representative density plots depicting PD-1 expression on CD4 T cells from spinal cords of infected wild-type (WT) mice at the indicated days post-infection (p.i).; numbers within plots represent percentage of PD-1-positive CD4 T cells. Data are representative of two independent experiments with three mice per time point. (B) Interferon (IFN)-γ, interleukin (IL)-2, IL-10, and IL-21 transcripts in purified CD4 T cells from WT or B7-H1−/− brains at 7 days p.i. Transcript levels relative to GAPDH × 1000 are presented as fold change with levels from WT samples set at 1. Expression levels relative to GAPDH in WT samples were as follows: IFN-γ = 60; IL-10 = 55; IL-21 = 41; and IL-2 = 1.1. Data depict the mean ± SEM of two independent experiments.