♦ See referenced article, J. Biol. Chem. 2013, 288, 27519–27532
T cells have slight differences in glycosylation as they go through development, activation, and aging. These differences control the cells' receptor activation and apoptosis susceptibility through the interaction with lectins. Not much is known about the pathways that determine which sugars are exposed during T cell activation and lectin interactions. In this Paper of the Week, a team led by Sandra J. van Vliet at the VU University Medical Center in The Netherlands demonstrated that the ERK and calcineurin pathways put N-acetylgalactosamines (GalNAc) on surfaces of certain T cells that allow a lectin called the macrophage galactose-type lectin (MGL) to bind to them. The binding of MGL to these T cells, which are newly activated, reduces their receptor signaling and cytokine responses and causes apoptosis. “Understanding the mechanisms that control GalNAc exposure may aid the development of novel strategies to intervene in inappropriate T cell activation as observed in chronic inflammatory and autoimmune disorders,” say the authors.
Schematic representation of the T cell signaling pathways that control the exposure of MGL-binding ligands on activated CD4+ T cells. Triggering of the ERK-MAPK and calcineurin-NFAT cascades results in diminished expression and activity of the core 1 β3GalT-Cosmc complex via an as yet unidentified factor, which is neither AP-1 nor NF-κB.