FIG. 6.

T-cell suppression by retinal cells from Toxoplasma-infected retinas is PD-L1 dependent. (A) Splenic T cells isolated from cpsII-vaccinated mice were incubated with STAg alone (shaded bar) or STAg-loaded splenic APCs in the presence of increasing numbers (1 × 10⁵, 5 × 10⁴, or 1 × 10⁴) of retinal cells from either mock-infected (filled bars) or parasite-infected (open bars) mice. Shown are the averages for quadruplicate samples repeated two independent times. *, P < 0.005 by a two-tailed, unpaired Student t test. (B) Splenic T cells from vaccinated mice were incubated with STAg alone (shaded bar) or with STAg-loaded DCs in the absence or presence of parasite-infected retinal cells. Pyrimethamine (1 μM) was included as indicated. Shown are results of a representative experiment repeated three times in quadruplicate. *, P < 0.005 by Student's t test. (C) Splenic T cells from vaccinated mice were incubated with the indicated cells (5 × 10⁴ parasite-infected retinal cells were used where indicated) and antibodies. Shown are results of a representative experiment carried out in quadruplicate. Asterisks indicate significance by Student's t test (**, P < 0.01; *, P < 0.05).