β-Galactoside-binding protein secreted by activated T cells inhibits antigen-induced proliferation of T cells

Abstract

We have used mRNA differential display PCR to search for genes induced in activated T cells and have found the LGALS1 (lectin, galactoside-binding, soluble) gene to be strongly up-regulated in effector T cells. The protein coded by the LGALS1 gene is a β-galactoside-binding protein (βGBP), which is released by cells as a monomeric negative growth factor but which can also associate into homodimers (galectin-1) with lectin properties. Northern blot analysis revealed that ex vivo isolated CD8⁺ effector T cells induced by a viral infection expressed high amounts of LGALS1 mRNA, whereas LGALS1 expression was almost absent in resting CD8⁺ T cells. LGALS1 expression could be induced in CD4⁺ and CD8⁺ T cells upon activation with the cognate peptide antigen and high levels of LGALS1 expression were found in concanavalin A-activated T cells but not in lipopolysaccharide-activated B cells. Gel filtration and Western blot analysis revealed that only monomeric βGBP was released by activated CD8⁺ T cells and in vitro experiments further showed that recombinant βGBP was able to inhibit antigen-induced proliferation of naive and antigen-experienced CD8⁺ T cells. Thus, these data indicate a role of βGBP as an autocrine negative growth factor for CD8⁺ T cells.