Critical role of heme oxygenase-1 in Foxp3-mediated immune suppression

Foxp3, which encodes the transcription factor scurfin, is indispensable for the development and function of CD4+CD25+ regulatory T cells (Treg). Recent data suggest conversion of peripheral CD4+CD25− naı¨ve T cells to CD4+CD25+ Treg by acquisition of Foxp3 through costimulation with TCR and TGF-β or forced expression of the gene. One critical question is how Foxp3 causes T cells to become regulatory. In the present work, we demonstrate that Foxp3 can induce heme oxygenase-1 (HO-1) expression and subsequently such regulatory phenotypes as the suppression of nontransfected cells in a cell-cell contact-dependent manner as well as impaired proliferation and production of cytokines upon stimulation in Jurkat T cells. Moreover, we confirm the expression of both Foxp3 and HO-1 in peripheral CD4+CD25+ Treg and suppressive function of the cells are relieved by the inhibition of HO-1 activity. In summary, we demonstrate that Foxp3 induces HO-1 expression and HO-1 engages in Foxp3-mediated immune suppression.