Blockade of programmed death-1 in young (New Zealand Black x New Zealand White)F1 mice promotes the suppressive capacity of CD4+ regulatory T cells protecting from lupus-like disease.

Programmed death-1 (PD-1) usually acts as a negative signal for T cell activation, and its expression on CD8(+)Foxp3(+) T cells is required for their suppressive capacity. In this study, we show that PD-1 signaling is required for the maintenance of functional regulatory CD4(+)CD25(+)Foxp3(+) regulatory T cells (CD4(+) T(reg)) that can control autoimmunity in (New Zealand Black × New Zealand White)F1 lupus mice. PD-1 signaling induced resistance to apoptosis and prolonged the survival of CD4(+) T(reg). In vivo, the blockade of PD-1 with a neutralizing Ab reduced PD-1 expression on CD4(+) T(reg) (PD1(lo)CD4(+) T(reg)). PD1(lo)CD4(+) T(reg) had an increased ability to promote B cell apoptosis and to suppress CD4(+) Th as compared with CD4(+) T(reg) with elevated PD-1 expression (PD1(hi)CD4(+) T(reg)). When PD-1 expression on CD4(+) T(reg) was blocked in vitro, PD1(lo)CD4(+) T(reg) suppressed B cell production of IgG and anti-dsDNA Ab. Finally, in vitro studies showed that the suppressive capacity of CD4(+) T(reg) depended on PD-1 expression and that a fine-tuning of the expression of this molecule directly affected cell survival and immune suppression. These results indicate that PD-1 expression has multiple effects on different immune cells that directly contribute to a modulation of autoimmune responses.