In contrast to PD-1, Treg cell expression of CTLA-4 provides an effector mechanism that can limit autoimmune inflammation, but total loss of CTLA-4 results in enhanced Treg cell populations (38, 39) and lineage specific deletion of CTLA-4 in Treg cells results in enhanced Treg cell activities in models of autoimmunity (20). This evidence concerns the gene CTLA4 and Autoimmunity.