Fig. 4.

PD-1 expression was related to the suppressive activity of CD4⁺FoxP3⁺ Treg cells. A: PD-1 deficiency impaired the suppressive function of Treg cells from PD-1KO mice. B: CD4⁺PD-1⁺GFP⁺ Treg cells had greater suppression than CD4⁺PD-1⁻GFP⁺ Treg cells from FoxP3-GFP “knock-in” mice. CD4⁺FoxP3⁺ (in A) or CD4⁺PD-1⁺GFP⁺ and CD4⁺PD-1⁻GFP⁺ (in B) cells were sorted from splenocytes of immunized PD-1KO and WT B6 mice (in A) or FoxP3-GFP “knock-in” mice (in B). The suppressive activities of CD4⁺FoxP3⁺ cells from PD-1KO vs. WT mice or CD4⁺PD-1⁺GFP⁺ vs. CD4⁺PD-1⁻GFP⁺ from FoxP3-GFP “knock-in” mice were compared ex vivo by using the T-cell suppression assay. CD4⁺FoxP3⁻ (in A) or CD4⁺GFP⁻ (in B) cells from the same batch of mice were used as responder cells and T-cell-depleted splenocytes from naïve WT mice were used as APCs. The experiment was repeated twice with five mice per group in each experiment.