Expression of functional GPR35 in human iNKT cells

The aim of this study was to examine the expression of G protein-coupled receptor (GPR)35 in human invariant natural killer T (iNKT) cells and to determine the functional effects induced by selective activation of this receptor. RT-PCR analysis showed that both human iNKT cells and resting PBMC expressed GPR35; GPR35 protein resulted mostly localized in the plasma membrane, while it internalized in punctate intracellular structures following specific receptor activation (Western blot and immunofluorescence/confocal microscopy analysis). The specific activation of GPR35 by selective receptor agonists [l-kynurenic acid (KYNA)] or 1,4-dihydro-5-(2-propoxyphenyl)-7H-1,2,3-triazolo [4,5-d]pyrimidine-7-one (zaprinast)] functionally correlated with a significant reduction in IL-4 release from α-galactosylceramide (α-GalCer)-activated human iNKT cells, and this effect resulted mediated by pertussis toxin (PTX)-sensitive Gi/o proteins.In conclusion, our results demonstrate that human iNKT cells express GPR35 functionally active in reducing IL-4 release.

Research highlights
► Human invariant NKT (iNKT) cells express GPR35 at both gene and protein levels.
► GPR35 internalize in human iNKT cells following receptor activation.
► Specific GPR35 agonists significantly reduce the release of IL-4, but not that of IFN-γ.
► GPR35 couples Gi/o proteins in human iNKT cells.