Blood 114: 1355-1365 (2009)

Activation-induced cell death (AICD) plays an essential role in the contraction of activated T cells after eradication of pathogen. Fas (APO-1/CD95) is one of the key cell surface proteins that mediate AICD in CD4 (+) and CD8 (+) T cells. Despite its prime importance in cell death, regulation of Fas expression in T cells is poorly understood. Here we show that Cyclon, a newly identified cytokine-inducible protein, is induced in T cells on T-cell receptor ligation and important for immune homeostasis. We showed that Cyclon enhances AICD through upregulation of Fas expression. We think that our data provide insight into expression regulation of Fas in T cells.