Antagonic functions of galectin-8 on cells of the immune system.

MARÍA VIRGINIATRIBULATTI , JUAN MUCCI, VALENTINA CATTANEO Y OSCAR CAMPETELLA

Rosario, Santa Fé, Argentina.

Congreso; XLII Reunión Anual de la Sociedad Argentina de Investigación en Bioquímica y Biología Molecular; 2006

Galectins are mammalian lectins that bind galactosyl residues. Galectin-8 (Gal-8) is a tandem repeat-type galectin, presenting two carbohydrate binding-domains joined by a linker peptide. In contrast to Gal-1 and 3, which were extensively studied in their roles in the immune system, little is known about Gal-8. We have determined by RT-PCR and western-blot the presence of Gal-8 in thymocytes, thymic epithelial cells and splenocytes. Thymocytes and splenocytes were incubated with 0,5ìM of recombinant Gal-8. In thymocytes, apoptosis induction triggered by caspase-3 activation was observed, as assessed by substrate cleavage and flow cytometry. In contrast, Gal-8 induced proliferation of splenocytes as determined by 3H thymidine incorporation. This effect was also seen with splenocytes from nude mice, indicating that B cells were activated directly. Apoptosis and proliferation were fully prevented when a galactose analog (TDG) was included in the assays, demonstrating that these effects were caused by the Gal-8 sugar-binding ability. In order to identify potentials ligands for Gal-8 in the spleen, a pull-down assay was performed. Biotinylated membrane proteins of splenocytes from nude or wt mice were employed and defined bands were revealed in both cases. These data support a divergent role for Gal-8 among different immune system compartments.