10779/crick.11637927.v1 Carrie R Willcox Carrie R Willcox Pierre Vantourout Pierre Vantourout Mahboob Salim Mahboob Salim Iva Zlatareva Iva Zlatareva Daisy Melandri Daisy Melandri Leonor Zanardo Leonor Zanardo Roger George Roger George Svend Kjaer Svend Kjaer Mark Jeeves Mark Jeeves Fiyaz Mohammed Fiyaz Mohammed Adrian C Hayday Adrian C Hayday Benjamin E Willcox Benjamin E Willcox Butyrophilin-like 3 directly binds a human Vγ4+ T cell receptor using a modality distinct from clonally-restricted antigen The Francis Crick Institute 2020 T cell receptor butyrophilin complementarity determining region gamma delta T cell ligand selection Hayday FC001093 SB 1107 Immunology Immunology 2020-01-17 16:56:39 Journal contribution https://crick.figshare.com/articles/journal_contribution/Butyrophilin-like_3_directly_binds_a_human_V_4_T_cell_receptor_using_a_modality_distinct_from_clonally-restricted_antigen/11637927 Butyrophilin (BTN) and butyrophilin-like (BTNL/Btnl) heteromers are major regulators of human and mouse γδ T cell subsets, but considerable contention surrounds whether they represent direct γδ T cell receptor (TCR) ligands. We demonstrate that the BTNL3 IgV domain binds directly and specifically to a human Vγ4+ TCR, "LES" with an affinity (∼15-25 μM) comparable to many αβ TCR-peptide major histocompatibility complex interactions. Mutations in germline-encoded Vγ4 CDR2 and HV4 loops, but not in somatically recombined CDR3 loops, drastically diminished binding and T cell responsiveness to BTNL3-BTNL8-expressing cells. Conversely, CDR3γ and CDR3δ loops mediated LES TCR binding to endothelial protein C receptor, a clonally restricted autoantigen, with minimal CDR1, CDR2, or HV4 contributions. Thus, the γδ TCR can employ two discrete binding modalities: a non-clonotypic, superantigen-like interaction mediating subset-specific regulation by BTNL/BTN molecules and CDR3-dependent, antibody-like interactions mediating adaptive γδ T cell biology. How these findings might broadly apply to γδ T cell regulation is also examined.