Structures of human γδ T cell receptor-CD3 complex.

Gamma delta (γδ) T cells, a unique T cell subgroup, are crucial in various immune responses and immunopathology1-3. The γδ T cell receptor (TCR), which is generated by γδ T cells, recognizes a diverse range of antigens independently of the major histocompatibility complex2. The γδ TCR associates with CD3 subunits, initiating T cell activation and holding great potential in immunotherapy4. Here we report the structures of two prototypical human Vγ9Vδ2 and Vγ5Vδ1 TCR-CD3 complexes5,6, revealing two distinct assembly mechanisms that depend on Vγ usage. The Vγ9Vδ2 TCR-CD3 complex is monomeric, with considerable conformational flexibility in the TCRγ-TCRδ extracellular domain and connecting peptides. The length of the connecting peptides regulates the ligand association and T cell activation. A cholesterol-like molecule wedges into the transmembrane region, exerting an inhibitory role in TCR signalling. The Vγ5Vδ1 TCR-CD3 complex displays a dimeric architecture, whereby two protomers nestle back to back through the Vγ5 domains of the TCR extracellular domains. Our biochemical and biophysical assays further corroborate the dimeric structure. Importantly, the dimeric form of the Vγ5Vδ1 TCR is essential for T cell activation. These findings reveal organizing principles of the γδ TCR-CD3 complex, providing insights into the unique properties of γδ TCR and facilitating immunotherapeutic interventions.

Structural variability and concerted motions of the T cell receptor - CD3 complex.

We investigate the structural and orientational variability of the membrane-embedded T cell receptor (TCR) - CD3 complex in extensive atomistic molecular dynamics simulations based on the recent cryo-EM structure determined by Dong et al., 2019. We find that the TCR extracellular (EC) domain is highly variable in its orientation by attaining tilt angles relative to the membrane normal that range from 15° to 55°. The tilt angle of the TCR EC domain is both coupled to a rotation of the domain and to characteristic changes throughout the TCR - CD3 complex, in particular in the EC interactions of the Cß FG loop of the TCR, as well as in the orientation of transmembrane helices. The concerted motions of the membrane-embedded TCR - CD3 complex revealed in our simulations provide atomistic insights on conformational changes of the complex in response to tilt-inducing forces on antigen-bound TCRs.

Structural biology of the T-cell receptor: insights into receptor assembly, ligand recognition, and initiation of signaling.

The T-cell receptor (TCR)-CD3 complex serves as a central paradigm for general principles of receptor assembly, ligand recognition, and signaling in the immune system. There is no other receptor system that matches the diversity of both receptor and ligand components. The recent expansion of the immunological structural database is beginning to identify key principles of MHC and peptide recognition. The multicomponent assembly of the TCR complex illustrates general principles used by many receptors in the immune system, which rely on basic and acidic transmembrane residues to guide assembly. The intrinsic binding of the cytoplasmic domains of the CD3epsilon and zeta chains to the inner leaflet of the plasma membrane represents a novel mechanism for control of receptor activation: Insertion of critical CD3epsilon tyrosines into the hydrophobic membrane core prevents their phosphorylation before receptor engagement.

Single-molecule microscopy reveals heterogeneous dynamics of lipid raft components upon TCR engagement.

The existence of lipid rafts and their importance for immunoreceptor signaling is highly debated. By non-invasive single molecule imaging, we analyzed the dynamics of the T-cell antigen receptor (TCR), the lipid raft-associated glycosylphosphatidylinositol (GPI) proteins CD48 and CD59 and the major leukocyte phosphatase CD45 in living naive T lymphocytes. TCR triggering induced the immobilization of CD45 and CD48 at different positions within the T-cell interface. The second GPI protein, CD59, did not co-immobilize indicating lipid raft heterogeneity in living T lymphocytes. A novel biochemical approach confirmed that lipid raft components are not associated in the plasma membrane of resting cells, and variably associate with specific receptors to distinct lipid rafts upon activation.

Morphologic examination of CD3-CD4(bright) cells in rat liver.

Recently, we found CD3-CD4(bright) cells with comparative specificity for normal rat liver. In the current study, we investigated the type and form of both CD3-CD4(bright) cells and CD3-CD4(dull) cells in the rat liver. The surface phenotype of hepatic mononuclear cells in Lewis rats was identified by using monoclonal antibodies including anti-CD4, anti-CD3, and antimacrophage in conjunction with two- or three-color immunofluorescence analysis. CD3-CD4(bright) cells and CD3-CD4(dull) cells were examined morphologically using May-Giemsa staining and scanning electron microscopy. The distribution of CD3-CD4(bright) cells and CD3-CD4(dull) cells 48 hours after intravenous administration of liposome-encapsulated dichloromethylene diphosphate was also investigated. In comparison to CD3-CD4(dull) cells, CD3-CD4(bright) cells were slightly larger macrophages with abundant cytoplasmic granules, being present with comparative specificity for normal rat liver and showing negligible effects by intravenous liposome-encapsulated dichloromethylene diphosphate administration. These data suggest that in normal young rat liver these CD3-CD4(dull) and CD3-CD4(bright) cells may be dendritic cells and Kupffer cells that shift from the liver to the spleen or vice versa. These cells may also be able to locally proliferate in liver or spleen due to changes in the developing liver.