IMMUNOBIOLOGY Galectin-1: a key effector of regulation mediated by CD4CD25 T cells

The naturally occurring population of dedicated regulatory T cells that co-express CD4 and CD25 is known to play a key role in the maintenance of peripheral T-cell tolerance; however, their mecha-nism of action has remained obscure. Here we report that a member of the family of -galactoside–binding proteins, galectin-1, is overexpressed in regulatory T cells, and that expression is increased after activation. Most importantly, block-ade of galectin-1 binding significantly reduced the inhibitory effects of human and mouse CD4CD25 T cells. Reduced regulatory activity was observed in CD4CD25Tcellsobtainedfromgalectin-1– homozygous null mutant mice. These re-sults suggest that galectin-1 is a key effec-tor of the regulation mediated by these cells