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 g-galactoside-binding protein (g GBP), 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 g GBP was released by activated CD8 + T cells and in vitro experiments further showed that recombinant g GBP was able to inhibit antigen-induced proliferation of naive and antigen-experienced CD8 + T cells. Thus, these data indicate a role of g GBP as an autocrine negative growth factor for CD8 + T cells.

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Chick embryo cells: These were obtained from 10-day-old chicks and grown in a tris0ay-droxymethyl)aminomethane-bffffered Gey's solution with peptone and lactalbumin hydrolysate (4). They were infected after 2 days' growth on coverslips or in 6 mm diameter Petri dishes.HeLa cdls: These were propagated in medium 199 plus 5 per cent inactivated calf serum and were infected 3 to 6 days after subculture by trypsinization. 463

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