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T cell receptors co-recognizing both MHC and antigenic peptide for a tri-party specific interaction has been a central dogma of T cell-mediated responses. Here the authors use X-ray crystallography to identify a TCR that contacts only the MHC beta chain of HLA-DQ2, with this specificity potentially enforced by Leucine-55 of HLA-DQ2.5 to exclude interaction with other MHCs.

Natural killer T cells (NKT cells) recognize lipid antigens presented by CD1d. Zajonc and Rossjohn and their colleagues describe molecular interactions between type II NKT cell antigen receptors and CD1d-ligand complexes, which demonstrate distinct modes of recognition used by the receptors.

Rossjohn, van der Vliet and colleagues develop single-___domain antibodies binding composite CD1d and NKT T-cell receptor antigens, inducing specific antitumor immune subsets.

Mucosal-associated invariant T (MAIT) cells recognize vitamin B metabolites presented by the molecule MR1. Rossjohn and colleagues generate multiple altered metabolite ligands and determine their structures in the context of MR1 and the TCR to develop a generalized framework for MAIT cell antigen recognition.

The mode by which NK cell receptors are bound to their ligands has been unclear. Rossjohn and colleagues show that the cytomegalovirus immunoevasin m157 binds the NK cell receptor Ly49 by its stalk region and not via the expected membrane-distal lectin ___domain.

The molecular mechanism of Goodpasture disease is modelled to mechanistically determine how a human leukocyte antigen (HLA) allele can exert its dominant protective effect in autoimmune disease.

In contrast to microbial natural killer T cell ligands, self glycolipid antigens are β-linked. Rossjohn and co-workers provide the mechanism for the autoreactivity of natural killer T cell antigen receptors toward β-glycosylated agonists.

CD1 molecules present diverse lipid ligands to TCRs expressed by NKT cells. Rossjohn, Moody and colleagues show a unique form of autoreactivity with human CD1c molecules, whereby TCRs recognize a closed conformation of CD1c molecules, which are loaded with a diverse array of ‘headless’ glycolipids.

Mucosal-associated invariant T cells recognize vitamin-B-derived ligands presented via the major-histocompatibility-complex-like molecule MR1. Rossjohn and colleagues demonstrate that these cells recognize a wide variety of ligands, some derived from common drugs, in an agonist or antagonist manner.

To date, structural analysis has demonstrated a highly consistent binding pattern of the TCR to the MHC molecule. Rossjohn and colleagues reveal the first structures of two human T_reg cell TCRs and show that they bind with a reversed polarity to the MHC.

CD1a presents a broad repertoire of lipid-based antigens. Rossjohn and colleagues show that the TCR docks over CD1a in a manner that precludes contact with permissive antigens, while nonpermissive antigens disrupt the TCR-CD1a contact.

MR1 molecules present bacterial metabolites to MAIT innate lymphocytes, but the processing and presentation pathway of these ligands are unclear. McCluskey, Rossjohn, Villadangos and colleagues demonstrate that MR1 ligands bind in the ER, which initiates trafficking to the plasma membrane and subsequent presentation.

Certain specific antigens have been shown to activate T cells in an MHC independent manner. Here the authors show a phycoerythrin reactive mouse TCR which recognises native protein and characterise the molecular nature of this interaction and that this specific TCR can be selected in the thymus.

Jamie Rossjohn and colleagues review the structural and functional data that provide insight into the MHC restriction of T cell receptors. They discuss the non-mutually exclusive contributions of intrinsic germline-encoded motifs and developmental selection to MHC restriction.

Natural killer T (NKT) cells include type I that express semi-invariant T cell receptor (TCR), and type II that cover a broader repertoire. Here the authors describe the crystal structure of a type II NKT TCR complexed with CD1d/antigen to propose that type II NKT TCRs may adapt multiple CD1d docking modes to maximise antigen recognition efficacy.

Epitopes formed by fusion of more than one self peptide, such as proinsulin and other β cell proteins, can result in the formation of non-self hybrid peptides that can potentially trigger autoimmune responses. Here the authors show how TRBV5 + T cell receptors are geared towards recognition of HLA-DQ8 bound hybrid peptides in patients with type 1 diabetes.

KIR2DL2 and KIR2DL3 are two inhibitory members of the killer-cell immunoglobulin-like receptors (KIR) family that share a common HLA-I preference in binding HLA from the C1 group. However, it is still unclear to what extent binding and function is equivalent between KIR2DL2 and 2DL3. Here, the authors present the crystal structures of KIR2DL2 and 2DL3 in complex with HLA-C*07:02 and observe differences in HLA-C recognition between KIR2DL2 and 2DL3, which correlates with differences in HLA-C binding preference as they show with mutagenesis and binding studies.

Structural, biochemical and cellular analyses show that bacterial antigens can mimic gliadin epitopes involved in celiac disease being presented by HLA-DQ2.5 and recognized by T cells derived from patients.

T cell receptors are generally thought to contact antigens presented in an end to end configuration. Here the authors show a geometrically alternate sideways mode of recognition of the antigen-presenting molecule CD1a by a γδ T cell receptor.

Presentation of signal peptides by HLA-E to natural killer cells prevents cell lysis via interactions with the inhibitory CD94–NKG2A receptor. A study now reveals an unexpected level of sophistication and heterogeneity in this receptor–ligand interaction.

Attachment of a piece of viral protein to a small RNA achieves transfer of the RNA into neuronal cells in cell culture. This was also able to deliver an antiviral siRNA specifically into the brains of mice infected with encephalitis and achieve 80% protection. This study opens a new potential line of treatment for neuronal disease.

Here, the authors discuss how the T cell receptors expressed by natural killer T cells are able to recognize and respond to an array of self and foreign lipid antigens that are presented on CD1d molecules. They explain how a better understanding of these processes could be exploited for therapeutic purposes.

The structure of the major histocompatibility complex (MHC)-class-I-like molecule MR1 in complex with a vitamin B9 derivative is determined; metabolites of vitamin B2 are shown to activate MR1-restricted mucosal-associated invariant T cells, implicating them in microbial immunosurveillance.

The invariant αβTCR of type I NKT cells recognizes a lipid α-GalCer presented by CD1d. Here the authors describe atypical α-GalCer-reactive NKT cells with diverse TCRs, which bind to CD1d-α-GalCer in a manner distinct from type I NKT cells, thus unveiling greater diversity in lipid antigen recognition.

HLA-C expression levels correlate with immune responses to pathogens and autoimmunity, and vary in an allele-specific manner across individuals. Here the authors identify factors that drive differential expression of HLA-C allomorphs at the cell surface, and influence the structure of the peptide-binding cleft and diversity of peptides bound by HLA-C molecules.

Germline-encoded mycolyl lipid-reactive (GEM) T cells recognize CD1b proteins presenting mycobacterial mycolates via their T-cell receptors (TCRs). Here, the authors present the structure of this interaction and provide a molecular basis for the co-recognition of CD1b and a mycobacterial glycolipid.

Shiga toxigenic Escherichia coli can cause gastrointestinal disease in humans, with potentially life-threatening consequences. This paper elucidates the mechanism of the bacteria-induced host cell death; a protein crucially involved in endoplasmic reticulum function is specifically targeted and inactivated by the toxin's protease subunit.

Human leukocyte antigen (HLA) presents peptides to activate T cells, but many aspects in the T cell receptor (TCR)/HLA interaction remain unclear. Here the authors show, via structural data, that two TCRs differentially recognize the same tumour peptide/HLA complex and induce contrasting conformation changes of the peptide.

Cross-reactivity to dengue virus serotypes can trigger life-threatening inflammation. Culshaw et al. show that germline-encoded components of dengue-virus-specific TCRs influence antigen engagament and suggest that ‘innate-like’ recognition of the virus might underpin harmful cross-reactivity.

Human Langerhans cells express CD1a, but those in mice do not, which makes determination of its function on these cells challenging in vivo. Through the use of a transgenic mouse that expresses CD1a, Winau and colleagues demonstrate that Langerhans cells use CD1a to present contact allergens and self lipid antigens and thereby worsen inflammatory skin conditions.

Structural determination and analysis of HLA-I that presents an HIV-derived peptide to an NK cell receptor reveal that N-terminal extended epitope conformations contribute to immune recognition and mechanisms of HIV immune escape.

How γδ TCRs bind antigen presented by antigen-presenting molecules remains unclear. Godfrey and colleagues describe a population of human γδ T cells that interacts with CD1d and provide a molecular basis for how a γδ TCR binds CD1d–α-GalCer.

A central event in celiac disease (CD) is the recognition by TCRs of gluten epitopes presented by specific HLAs, with HLA-DQ2 being associated with 95% of CD cases. The molecular basis for these interactions are now revealed by crystal structures of TCRs from individuals with CD in complex with wheat gliadin epitopes presented by HLA-DQ2.

Cryogenic electron microscopy determines the structure of a fully assembled, MR1-reactive, human Vγ8Vδ3 TCR–CD3δγε₂ζ₂ complex bound by anti-CD3ε antibody Fab fragments.

CD4⁺ T cells recognising shared susceptibility epitope (SE) encoded HLA-DRB1 presenting citrullinated self-peptides are implicated in rheumatoid arthritis. Here the authors characterise the T cell receptor repertoire and structure during recognition of different citrullinated self-epitopes in HLA-DR4 transgenic mice and ACPA + RA patients.

Influenza B viruses are linked to significant morbidity and mortality, and yet their immunobiology is comparatively poorly understood. Here Menon et al identify influenza B virus-specific CD8⁺ T cell epitopes and characterise these in adults, children and the elderly.

Autoreactivity to myeloperoxidase (MPO) causes autoimmune vasculitis and severe glomerulonephritis. Here, Ooi et al. show that a Staphylococcus aureus plasmid encodes a peptide that is homologous to an immunodominant MPO epitope and induces anti-MPO autoimmunity and glomerulonephritis in mice.

Peptide epitopes represent the minimal immunogenic region of a protein antigen. In the light of new insights into the nature of immunogenic epitopes, and recent advances in peptide delivery, stability and design, Purcell and colleagues review developments in the field of peptide-based vaccines.

The symbiotic gut bacterium Bacteroides fragilis produces unique α-galactosylceramides from host dietary branched-chain amino acids, which are presented as CD1d ligands and immunomodulate natural killer T cells.

Natural killer T cells (NKT cells) recognize lipid-based antigens presented by CD1d. The mammalian glycolipid β-glucosylceramide, a ubiquitous self antigen for NKT cells, is upregulated by microbial danger signals, which leads to activation of NKT cells in the absence of foreign glycolipid antigen.

Natural killer (NK) cells eliminate damaged cells, but spare healthy ones by recognizing their expressed ligands via NK inhibitory receptors. Here the authors solve the structure of an NK inhibitory receptor, NKR-P1B, bound to its ligand, Clr-b, with further data suggesting a weak interaction and informing on the basis of missing-self recognition.

Lymphocyte activation gene 3 (LAG3) is an important checkpoint inhibitor molecule of immunotherapeutic interest. New crystal structures of LAG3 provide important insight into its molecular architecture, laying the groundwork for future basic and applied investigations.

CD1 proteins present lipid antigens to T cells via the T cell receptor. Here the authors describe T cell reactivity to human membrane lipid moieties and provide structural data to define a molecular mechanism of promiscuous recognition of self-derived phospholipids.