Galectin-1, an endogenous lectin produced by thymic epithelial cells, induces apoptosis of human thymocytes

Abstract

Galectin-1, a β-galactoside binding protein is produced by thymic epithelial cells binds to human thymocytes. We have previously reported that galectin-1 induces the apoptosis of activated T lymphocytes. Because the majority of thymocytes die via apoptosis while still within the thymus we tested whether galectin-1 could induce the apoptosis of these cells. We now report that in vitro exposure to galectin-1 induced apoptosis of two subsets of CD4(lo) CD8(lo) thymocytes. The phenotypes of susceptible thymocytes were consistent with that of both negatively selected nonselected cells. Galectin- 1-Induced apoptosis was enhanced by preexposure of thymocytes to antibody to CD3 suggesting that galectin-1 may be a participant in T-cell-receptor mediated apoptosis. In contrast pretreatment of thymocytes with dexamethasone had no effect on galectin-1 susceptibility. We noted that 71% of the cells undergoing apoptosis after galectin-1 treatment had a DNA content greater than 2N indicating that proliferating thymocytes were most sensitive to galectin-1. We propose that galectin-1 plays a role in the apoptosis of both negatively selected nonselected thymocytes that the susceptibility of thymocytes to galectin-1 is regulated in part by entry or exit from the cell cycle.