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Recognition of synthetic polyanionic ligands underlies "spontaneous" reactivity of V?1 ??TCRs.

ABSTRACT: Although ??TCRs were discovered more than 30 yr ago, principles of antigen recognition by these receptors remain unclear and the nature of these antigens is largely elusive. Numerous studies reported that T cell hybridomas expressing several V?1-containing TCRs, including the V?1V?6 TCR of ??NKT cells, spontaneously secrete cytokines. This property was interpreted as recognition of a self-ligand expressed on the hybridoma cells themselves. Here, we revisited this finding using a recently developed reporter system and live single cell imaging. We confirmed strong spontaneous signaling by V?1V?6 and related TCRs, but not by TCRs from several other ?? or innate-like ?? T cells, and demonstrated that both ? and ? chains contributed to this reactivity. Unexpectedly, live single cell imaging showed that activation of this signaling did not require any interaction between cells. Further investigation revealed that the signaling is instead activated by interaction with negatively charged surfaces abundantly present under regular cell culture conditions and was abrogated when noncharged cell culture vessels were used. This mode of TCR signaling activation was not restricted to the reporter cell lines, as interaction with negatively charged surfaces also triggered TCR signaling in ex vivo V?1 ?? T cells. Taken together, these results explain long-standing observations on the spontaneous reactivity of V?1V?6 TCR and demonstrate an unexpected antigen presentation-independent mode of TCR activation by a spectrum of chemically unrelated polyanionic ligands.

SUBMITTER: Dunst J

PROVIDER: S-EPMC7317387 | biostudies-literature | 2020 Jun

REPOSITORIES: biostudies-literature

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Recognition of synthetic polyanionic ligands underlies "spontaneous" reactivity of Vγ1 γδTCRs.

Dunst Josefine J Glaros Vassilis V Englmaier Lukas L Sandoz Patrick A PA Önfelt Björn B Kisielow Jan J Kreslavsky Taras T

Journal of leukocyte biology 20200113 6

Although γδTCRs were discovered more than 30 yr ago, principles of antigen recognition by these receptors remain unclear and the nature of these antigens is largely elusive. Numerous studies reported that T cell hybridomas expressing several Vγ1-containing TCRs, including the Vγ1Vδ6 TCR of γδNKT cells, spontaneously secrete cytokines. This property was interpreted as recognition of a self-ligand expressed on the hybridoma cells themselves. Here, we revisited this finding using a recently develop ...[more]

PMID: 31943366

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Project description:Given the limited set of T cell receptor (TCR) V genes that are used to create TCRs that are reactive to different ligands, such as major histocompatibility complex (MHC) class I, MHC class II, and MHC-like proteins (for example, MIC molecules and CD1 molecules), the V?1 segment can be rearranged with D?-J?-C? or J?-C? segments to form classical ??TCRs or uncommon ??TCRs using a V?1 segment (?/??TCR). Here we have determined two complex structures of the ?/??TCRs (S19-2 and TU55) bound to different locus-disparate MHC class I molecules with HIV peptides (HLA-A*2402-Nef138-10 and HLA-B*3501-Pol448-9). The overall binding modes resemble those of classical ??TCRs but display a strong tilt binding geometry of the V?1 domain toward the HLA ?1 helix, due to a conserved extensive interaction between the CDR1? loop and the N-terminal region of the ?1 helix (mainly in position 62). The aromatic amino acids of the CDR1? loop exploit different conformations ("aromatic ladder" or "aromatic hairpin") to accommodate distinct MHC helical scaffolds. This tolerance helps to explain how a particular TCR V region can similarly dock onto multiple MHC molecules and thus may potentially explain the nature of TCR cross-reactivity. In addition, the length of the CDR3? loop could affect the extent of tilt binding of the V?1 domain, and adaptively, the pairing V? domains adjust their mass centers to generate differential MHC contacts, hence probably ensuring TCR specificity for a certain peptide-MHC class I (pMHC-I). Our data have provided further structural insights into the TCR recognition of classical pMHC-I molecules, unifying cross-reactivity and specificity.IMPORTANCE The specificity of ?? T cell recognition is determined by the CDR loops of the ??TCR, and the general mode of binding of ??TCRs to pMHC has been established over the last decade. Due to the intrinsic genomic structure of the TCR ?/? chain locus, some V? segments can rearrange with the C? segment, forming a hybrid V?C?V?C? TCR, the ?/??TCR. However, the basis for the molecular recognition of such TCRs of their ligands is elusive. Here an ??TCR using the V?1 segment, S19-2, was isolated from an HIV-infected patient in an HLA-A*24:02-restricted manner. We then solved the crystal structures of the S19-2 TCR and another ?/??TCR, TU55, bound to their respective ligands, revealing a conserved V?1 binding feature. Further binding kinetics analysis revealed that the S19-2 and TU55 TCRs bind pHLA very tightly and in a long-lasting manner. Our results illustrate the mode of binding of a TCR using the V?1 segment to its ligand, virus-derived pHLA.

Dataset Information

Recognition of synthetic polyanionic ligands underlies "spontaneous" reactivity of V?1 ??TCRs.

Publications

Recognition of synthetic polyanionic ligands underlies "spontaneous" reactivity of Vγ1 γδTCRs.

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