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From the * Department of Pathology and Laboratory Medicine, Galectin-1, a Molecular Biology Institute, and § Departments of Pediatrics, Microbiology and Immunology and the Jonsson Comprehensive Cancer
Center, University of California Los Angeles School of Medicine, Los Angeles, California 90095
-galactoside binding protein, is produced by thymic epithelial cells and 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 CD4lo CD8lo
thymocytes. The phenotypes of susceptible thymocytes were consistent with that of both negatively selected and 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 and nonselected thymocytes, and that the susceptibility of thymocytes to galectin-1 is regulated, in part, by entry or exit from the cell cycle.
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