Saracin: A Lectin from Saraca indica Seed Integument Induces Apoptosis in Human T-Lymphocytes

Saracin, a seed integument lectin from Saraca indica is highly specific for binding N-acetyl-neuraminyl-N-acetyllactosamine [Neu5Ac-α-(2-6)/(2-3)-d-Gal-β-(1-4)-d-GlcNAc]. This lectin has been found to be mitogenic for human lymphocytes, and this mitogenic activity could be inhibited in presence of fetuin. Further, treatment with saracin could induce secretion of IL-2 in a culture of resting human peripheral blood mononuclear cells (PBMC) after 48 h. Saracin has a higher affinity for the CD8+ than CD4+ T cells as revealed by FACS analysis. Agarose gel electrophoresis of DNA isolated from lymphocytes cultured under different conditions has shown that this lectin could induce apoptosis in activated T-lymphocytes, as also confirmed by flow cytometric studies. Phenotypic analysis of the apoptotic cells reveals that they belong to CD8+ T cells lineage. Four surface glycoproteins of PBMC have been found to interact with saracin in a trisaccharide [Neu5Ac-α-(2-6)/(2-3)-d-Gal-β-(1-4)-d-GlcNAc]-sequence specific manner. Saracin seems to be an interesting immunomodulator for the mammalian immune system.