Apoptosis of T cells mediated by galectin-1

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Abstract
GALECTIN-1, a member of the family of β-galactoside binding proteins1, has growth regulatory and immunomodulatory activities2–4. We report here that galectin-1, expressed by stromal cells in human thymus and lymph nodes5,6, is present at sites of cell death by apoptosis during normal T-cell development and maturation. Galectin-1 induced apoptosis of activated human T cells and human T leukaemia cell lines. Resting T cells also bound galectin-1, but did not undergo apoptosis. Human endothelial cells that expressed galectin-1 induced apoptosis of bound T cells. Galectin-1-induced apoptosis required expression of CD45, and was decreased when N-glycan elongation was blocked by treatment of the cells by swainsonine7, whereas inhibition of O-glycan elongation8 potentiated the apoptotic effect of galectin-1. Induction of apoptosis by an endogenous mammalian lectin represents a new mechanism for regulating the immune response.