Table I.

Importance of CTLA-4 on Treg cells.

Status of CTLA-4	Changes in Treg functions	Effects on mouse model
Present	Cell cycle arrest, but resistance against AICD (58); Suppresses Tcon cell activity and proliferation, controls cytokine production (58,59)	Inhibits AMA production, intrahepatic T-cell infiltration, and bile duct damage (80), and may relieve autoimmunity and inflammatory bowel disease (59)
Absent	Increases the frequencies of Foxp3+T cells, leads to Treg expansion but the cells were prone to apoptosis (58,74); remains functionally suppressive and produces an overabundance of IL-10 (74)	Lethal lymphoproliferative disease (73) Protection from EAE (58)

CTLA-4, cytotoxic T lymphocyte-associated antigen-4; Treg, regulatory T cells; ACID, activation-induced cell death; Tcon cells, conventional CD4⁺ T cells; AMA, anti-mitochondrial antibodies; Foxp3, forkhead box P3; IL, interleukin; EAE, experimental autoimmune encephalomyelitis.