Phosphoantigen sensing combines TCR-dependent recognition of the BTN3A IgV domain and germline interaction with BTN2A1
Carrie R. Willcox,
Mahboob Salim,
Charlotte R. Begley,
Mohindar M. Karunakaran,
Emily J. Easton,
Carlotta von Klopotek,
Katie A. Berwick,
Thomas Herrmann,
Fiyaz Mohammed,
Mark Jeeves,
Benjamin E. Willcox
Affiliations
Carrie R. Willcox
Institute of Immunology and Immunotherapy, University of Birmingham, Birmingham, UK; Cancer Immunology and Immunotherapy Centre, University of Birmingham, Birmingham, UK; Corresponding author
Mahboob Salim
Institute of Immunology and Immunotherapy, University of Birmingham, Birmingham, UK; Cancer Immunology and Immunotherapy Centre, University of Birmingham, Birmingham, UK
Charlotte R. Begley
Institute of Immunology and Immunotherapy, University of Birmingham, Birmingham, UK; Cancer Immunology and Immunotherapy Centre, University of Birmingham, Birmingham, UK
Mohindar M. Karunakaran
Institute for Virology and Immunobiology, University of Würzburg, Würzburg, Germany
Emily J. Easton
Institute of Immunology and Immunotherapy, University of Birmingham, Birmingham, UK; Cancer Immunology and Immunotherapy Centre, University of Birmingham, Birmingham, UK
Carlotta von Klopotek
Institute for Virology and Immunobiology, University of Würzburg, Würzburg, Germany
Katie A. Berwick
Institute of Immunology and Immunotherapy, University of Birmingham, Birmingham, UK; Cancer Immunology and Immunotherapy Centre, University of Birmingham, Birmingham, UK
Thomas Herrmann
Institute for Virology and Immunobiology, University of Würzburg, Würzburg, Germany
Fiyaz Mohammed
Institute of Immunology and Immunotherapy, University of Birmingham, Birmingham, UK; Cancer Immunology and Immunotherapy Centre, University of Birmingham, Birmingham, UK
Mark Jeeves
Henry Wellcome Building for NMR, Institute of Cancer and Genomic Sciences, University of Birmingham, Birmingham, UK; Corresponding author
Benjamin E. Willcox
Institute of Immunology and Immunotherapy, University of Birmingham, Birmingham, UK; Cancer Immunology and Immunotherapy Centre, University of Birmingham, Birmingham, UK; Corresponding author
Summary: Vγ9Vδ2 T cells play critical roles in microbial immunity by detecting target cells exposed to pathogen-derived phosphoantigens (P-Ags). Target cell expression of BTN3A1, the “P-Ag sensor,” and BTN2A1, a direct ligand for T cell receptor (TCR) Vγ9, is essential for this process; however, the molecular mechanisms involved are unclear. Here, we characterize BTN2A1 interactions with Vγ9Vδ2 TCR and BTN3A1. Nuclear magnetic resonance (NMR), modeling, and mutagenesis establish a BTN2A1-immunoglobulin V (IgV)/BTN3A1-IgV structural model compatible with their cell-surface association in cis. However, TCR and BTN3A1-IgV binding to BTN2A1-IgV is mutually exclusive, owing to binding site proximity and overlap. Moreover, mutagenesis indicates that the BTN2A1-IgV/BTN3A1-IgV interaction is non-essential for recognition but instead identifies a molecular surface on BTN3A1-IgV essential to P-Ag sensing. These results establish a critical role for BTN3A-IgV in P-Ag sensing, in mediating direct or indirect interactions with the γδ-TCR. They support a composite-ligand model whereby intracellular P-Ag detection coordinates weak extracellular germline TCR/BTN2A1 and clonotypically influenced TCR/BTN3A-mediated interactions to initiate Vγ9Vδ2 TCR triggering.
