BETA-GALACTOSIDE BINDING-PROTEIN SECRETED BY ACTIVATED T-CELLS INHIBITS ANTIGEN-INDUCED PROLIFERATION OF T-CELLS

We have used mRNA differential display PCR to search for genes induced in activated T cells and have found the LGALS1 (lectin, galactoside-b inding, soluble) gene to be strongly upregulated in effector T cells. The protein coded by the LGALS1 gene is a beta-galactoside-binding pro tein (beta GBP), which is released by cells as a monomeric negative gr owth factor but which can also associate into homodimers (galectin-1) with lectin properties. Northern blot analysis revealed that ex vivo i solated CD8(+) effector T cells induced by a viral infection expressed high amounts of LGALS1 mRNA, whereas LGALS1 expression was almost abs ent in resting CD8(+) T cells. LGALS1 expression could be induced in C D4(+) and CD8(+) T cells upon activation with the cognate peptide anti gen 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 bet a GBP was released by activated CD8(+) T cells and in vitro experiment s further showed that recombinant beta GBP was able to inhibit antigen -induced proliferation of naive and antigen-experienced CD8(+) T cells . Thus, these data indicate a role of beta GBP as an autocrine negativ e growth factor for CD8(+) T cells.