The heteromeric complex formed by dopamine receptor D5 and CCR9 leads the gut-homing of CD4+ T-cells upon inflammation.

ABSTRACT Background and Aims CD4+ T-cells constitute central players in inflammatory bowel diseases (IBD), driving inflammation in the gut-mucosa. Current evidence indicates that CCR9 and the integrin α4β7 are necessary and sufficient to imprint colonic homing on CD4+ T-cells upon inflammation. Interestingly, dopaminergic signalling has been previously involved in leukocyte homing. Despite dopamine levels are strongly reduced in the inflamed gut mucosa, the role of dopamine in the gut-homing of T-cells remains unknown. Here we study how dopaminergic signalling affects T-cells upon gut-inflammation. Methods Gut-inflammation was induced by transfer of naive T-cells into Rag1-/- mice or by administration of dextran sodium sulphate. T-cell migration and differentiation were evaluated by adoptive transfer of congenic lymphocytes followed by flow cytometry analysis. Protein interaction was studied by Bioluminescence Resonance Energy Transfer analysis, Bimolecular Fluorescence Complementation and in situ proximity ligation assays. Results We show the surface receptor providing colonic tropism to effector CD4+ T-cells upon inflammation is not CCR9 but the complex formed by CCR9 and the dopamine receptor D5 (DRD5). Assembly of the heteromeric complex was demonstrated in vitro and in vivo using samples from mouse and human origin. The CCR9:DRD5 heteroreceptor was upregulated in the intestinal mucosa of IBD patients. Signalling assays confirmed that complexes behave differently than individual receptors. Remarkably, the disruption of CCR9:DRD5 assembly attenuated the recruitment of CD4+ T-cells into the colonic mucosa. Conclusions Our findings describe a key homing receptor involved in gut-inflammation and introduce a new cell surface module in immune cells: macromolecular complexes formed by G protein-coupled receptors integrating the sensing of multiple molecular cues.