γδ T cell receptor recognition of CD1d in a lipid-independent manner

Abstract The monomorphic antigen-presenting molecule CD1d presents lipid antigens to both αβ and γδ T cells. Type I Natural Killer T cells (NKT) display exquisite specificity for CD1d presenting α-Galactosylceramide (α-GalCer), while the extent of lipid specificity exhibited by CD1d-restricted gd T cells remains unclear. Here we demonstrate that human γδ T cell receptors (TCRs) can recognise CD1d in either a lipid-dependent or auto-reactive manner with weak to moderate affinity. Using small-angle X-Ray scattering we identify ‘end-to-end’ γδ TCR-CD1d binding modality is conserved across distinct CD1d-restricted TCRs. In functional assays, CD1d presenting endogenous lipids was sufficient to stimulate γδ T cell lines. Moreover, CD1d alone induced γδ TCR-CD3 clustering and phosphorylation in a dose dependent manner while type I NKT TCR-CD3 clustering required α-GalCer. Elongation of the γδ TCR-CD3 complex by the inclusion of the Cγ2 and Cγ3 -encoded constant domains perturbed cellular activation whilst maintaining the ability to form functional γδ TCR clusters. The crystal structure of a Vδ1 γδ+ TCR-CD1d complex, showed that the gd TCR sat atop of the CD1d antigen-binding cleft but made no contacts to the presented lipid antigen. We provide a molecular basis for lipid-independent CD1d recognition by γδ TCRs.