Galectin-9 Controls the Activity of DR3 (TNFRSF25) in Suppressing Immunity

TNFR superfamily members are cell surface glycoprotein receptors that are either induced and/or constitutively expressed on various immune cell types. Previously we have shown that the membrane proximal extracellular region of the TNFR superfamily member 4-1BB, interacts with Galectin-9, and in turn facilitates oligomerization and/or clustering of 4-1BB molecules on the cell surface in a manner that allows efficient signaling. Galectin-9 is a member of the beta-galactoside binding lectin family of proteins that contain homologous carbohydrate recognition domains and typically bind to specific glycans of a glycoprotein. Consequently, a search for other TNFR superfamily glycoproteins that might be regulated by Galectin-9 revealed an interaction with the extracellular region of DR3 (TNFRSF25). DR3 is expressed on conventional CD4 + T cells and CD4 + Foxp3 + Treg cells and acts as a stimulatory receptor when ligated. Functional studies in vitro showed that the stimulatory activity of DR3 was in part dependent on Galectin-9 in that Galectin-9 −/− CD4 T cells were less responsive when DR3 was ligated. Furthermore, in vivo, where an agonist of DR3 can transiently induce Treg cell expansion in wild-type mice, we found that this effect of anti-DR3 was significantly lost in Galectin-9 −/− mice. Additionally, in EAE as well as Asthma models, where an agonist of DR3 can suppress disease via control of CD4 + Foxp3 + Treg cells, we found that this protective effect of anti-DR3 was lost in Galectin-9 −/− mice. Thus, our data demonstrate a novel function of Galectin-9 in facilitating signaling through DR3, and suggest that Galectin-9 may allow DR3 to oligomerize and/or cluster in a manner that allows efficient engagement of intracellular signaling pathways.