GRAIL Is Up-regulated in CD4+ CD25+ T Regulatory Cells and Is Sufficient for Conversion of T Cells to a Regulatory Phenotype

GRAIL (gene related to anergy in lymphocytes) is an ubiquitin-protein isopeptide ligase (E3) ubiquitin ligase necessary for the induction of CD4+ T cell anergy in vivo. We have extended our previous studies to characterize the expression pattern of GRAIL in other murine CD4+ T cell types with a described anergic phenotype. These studies revealed that GRAIL expression is increased in naturally occurring (thymically derived) CD4+ CD25+ T regulatory cells (mRNA levels 10-fold higher than naive CD25– T cells). Further investigation demonstrated that CD25+ Foxp3+ antigen-specific T cells were induced after a “tolerizing-administration” of antigen and that GRAIL expression correlated with the CD25+ Foxp3+ antigen-specific subset. Lastly, using retroviral transduction, we demonstrated that forced expression of GRAIL in a T cell line was sufficient for conversion of these cells to a regulatory phenotype in the absence of detectable Foxp3. These data demonstrate that GRAIL is differentially expressed in naturally occurring and peripherally induced CD25+ T regulatory cells and that the expression of GRAIL is linked to their functional regulatory activity.