T-Cell Receptor (TCR) Overview - US (2024)

T-cells are a subset of lymphocytes that play a large role in the immune response. The TCR (T-cell receptor) is a complex of integral membrane proteins that participate in the activation of T-cells in response to an antigen. Stimulation of TCR is triggered by MHC (major histocompatibility complex) molecules on cells with the antigen. Engagement of the TCR initiates positive and negative cascades that ultimately result in cellular proliferation, differentiation, cytokine production, and/or activation-induced cell death. These signaling cascades regulate T-cell development, homeostasis, activation, acquisition of effector’s functions and apoptosis [1, 2]. Thermo Fisher Scientific has a wide range of products to help with TCR research.

Key TCR Pathway Targets

TNF interacts with many pathway targets, including:

ATF2ERK1/2MEKK1
B7-1FynMKK3
B7-2GADSMKK4
BCL10GRAPMKK6
CARD11GRB2MKK7
CD3-gammaMHCNFAT
CD3-deltaIKKNF-κB
CD3-epsilonIL-2p38
CD3-zetaITAMPAG
CD4ITIMPAK
CD8JNKRac
CD28LATRaf1
CD45LckRas
c-JunMAGUKSHP2
CTLA4MALT1SIT
Elk1MAPKVHR
ERKMEKZAP70


TCR is composed of six different chains that form the TCR heterodimer responsible for ligand recognition. CD3 molecules are assembled together with the TCR heterodimer. CD3 possess a characteristic sequence motif for tyrosine phosphorylation, known as ITAMs (immunoreceptor tyrosine-based activation motifs). The TCR polypeptides themselves have very short cytoplasmic tails, and all proximal signaling events are mediated through the CD3 molecules. TCR-CD3 complex interaction plays an important role in mediating cell recognition events.

TCR Engagement and Tyrosine Phosphorylation

When TCRs are engaged by antigens the tyrosine phosphorylation of the ITAMs, present in the TCR-associated CD-zeta subunits, is triggered. Such ITAMs function by orchestrating the sequential activation of the Src-related PTKs: LcK and Fyn, which initiate TCR signaling, followed by that of ZAP70 (zeta-chain (TCR) associated protein kinase of 70 kDa), which further amplifies the response. Lck is activated by the interaction of MHC-II and CD4 or CD8. These various PTKs induce tyrosine phosphorylation of several polypeptides, including the transmembrane adaptor LAT (linker activator for T-cells). Protein tyrosine phosphorylation subsequently leads to the activation of multiple pathways, including ERK (extracellular signal regulated kinase), JNK (c-Jun N-terminal kinase), NF-κB and NFAT (nuclear factor of activated T-cells) pathways, which ultimately induce effector functions [3, 4, 5].

TCR Activation

TCR activation is regulated by various co-stimulatory receptors. CD28 provides an essential co-stimulatory signal during T-cell activation, which augments the production of IL-2 (Interleukin-2), increases T-cell proliferation and prevents the induction of anergy and cell death. Once ligated by B7-1 or B7-2, CD28 provides the T-cell with an initial adhesion capable of approximating the T-Cell and antigen presenting cell membranes.

Besides CD28, many other transmembrane receptors also modulate specific elements of TCR signaling. CD45 is one such receptor which regulates TCR signaling by modulating the phosphorylation state of the tyrosine kinases like Lck and Fyn, and antagonizing the inhibitory impact of inhibitory proteins, thereby favoring T-cell activation.

LAT is an integral membrane adaptor protein that resides in lipid membrane rafts and binds to the adaptor GADS (growth factor receptor-bound protein-2-related adaptor protein-2), SLP76 (SH2 domain-containing leukocyte protein-76), and ITK (IL-2 inducible T-cell kinase). LAT stimulates one critical protein PLC-gamma1 (phospholipase-C-gamma1) that is responsible for the production of the second messengers DAG (diacylglycerol) and IP3 (inositol triphosphate) by cleaving PIP2 (phosphatidylinositol-4,5-bisphosphate) at the plasma membrane.

Tyrosine-phosphorylated LAT also binds multiple members of the GRB2 family of adaptor proteins, such as GRB2, GRAP (GRB2- related adaptor protein) and GADS (GRB2 -related adaptor protein-2) to facilitate the assembly of macromolecular signaling complexes that are required for efficient T-cell activation. The interaction of tyrosine-phosphorylated LAT with GRB2 provides a mechanism by which GRB2 and GRAP-associated SOS are recruited to the plasma membrane and potentially activate Ras [6].

TCR activation also leads to cytoskeletal rearrangements through the activation of GTP-binding proteins Rac and PAK, downstream of ZAP70 [9, 10, 11].

MAPKs Activated by TCR Pathway

Activation of Ras leads to the activation of a number of serine/threonine kinases: Raf1, MEK (MAPK/ERK Kinase) and dual-specificity kinases that are responsible for the eventual upregulation of the MAPKs (mitogen activated protein kinases): ERK1/2. In contrast, ERK activation can also be downregulated by TCR signaling by phosphorylated VHR (dual specificity protein phosphatase VHR), a dual specific phosphatase, phosphorylated by ZAP70.

Other MAPKs like JNK and p38 are also activated by ZAP70 and SLP76, downstream of Vav. Vav in turn phosphorylates and activates the GTP-binding protein Rac which further mediates the activation of MEKK1 (MAP/ERK Kinase Kinase-1).

p38 is activated by MEKK1 through the activation of MKK3 (mitogen-activated protein kinase kinase-3)/MKK6. JNK is activated by MEKK1 through activation of MKK4 (mitogen-activated protein kinase kinase-4)/MKK7. These MAPKs directly phosphorylate transcription factors involved in the formation of the heterodimeric transcription factor, Jun-Fos complex, as well as NFAT and IL-2 (interleukin-2) gene expression in synergy with Ca2+ signaling. ERKs, JNK and p38 directly phosphorylate the transcription factors: Elk1, c-Jun and ATF2 (activating transcription factor-2) respectively. Another transcription factor important for the generation of IL-2 is NF-κB [6, 7, 8]. NF-κB members control the expression of various genes involved in inflammatory, apoptotic and immune responses [3]. Activation of NF-κB is dependent on stimulation of the TCR and co-stimulation via CD28.

Negative Regulation of TCR

Negative regulation of TCR signaling is also significant, in order to keep a check on the hyperactivation ofimmune response associated with the pathway. SIT (SHP2-interacting transmembrane adaptor protein) is a recently identified transmembrane adaptor protein, which interacts with the SHP2 (SH2-containing protein tyrosine phosphatase-2) via an ITIM (immunoreceptor tyrosine-based inhibition motif), and the complex acts as a critical negative regulator of TCR-mediated signaling [12, 13].

In resting human T-Cells, PAG (phosphoprotein associated with glycosphingolipid microdomains), a transmembrane adaptor molecule found in lipid rafts, is tyrosine phosphorylated and associated with CSK (c-Src tyrosine kinase), an inhibitor of Src-related protein tyrosine kinases. As a result, overexpression of PAG inhibits TCR-mediated responses. These modifications (association of PAG and CSK) are rapidly lost in response to TCR stimulation in order to maintain uninterrupted TCR signaling [7].

In addition, CTLA4 (cytotoxic T-lymphocyte antigen-4) also negatively regulates T-cell activation. The transmembrane protein CTLA4 also serves as a natural inhibitor. Once T-cells become activated, by whatever disease process is turning them on, the body has a natural process to turn down the T-cell pathways so that it does not get out of control.

After T-cell activation, CTLA4 is rapidly endocytosed, thus removing it rapidly from the cell surface. The significance of the apparent tight control of CTLA4 expression is due to the fact that CTLA4 has a greater affinity for its B7-1/B7-2 ligands in comparison to CD28; thus, when CTLA4 is not required, it is endocytosed, to maintain a fast T-cell activation response. When a need to control TCR signaling arises, ZAP70 activates the process of active release and translocation of CTLA4 to the membrane. At the membrane, CTLA4 interacts with the SHP2 and inhibits the phosphorylation of TCR. Another mechanism by which CTLA4 might antagonize T-cell function is through inhibition of CD28 signaling by competing for their shared ligands B7-1 and B7-2 [14, 15].

Every effective immune response involves T-cell activation. T-cells are especially important in cell-mediated immunity or the defense against tumor cells and pathogenic organisms inside cells. T-cells are also involved in rejection reactions. Deregulation of T-cell function, whether by defect or by excess, results in dire consequences for the organism. These consequences could include immunodeficiency and autoimmunity, respectively.

TCR is an extremely sensitive system. Very few peptide-MHC complexes on an antigen-presenting cell are needed to trigger a T-cell response. Since T-cells play various critical roles in orchestrating the immune responses, this knowledge should lead to an understanding of how breakdowns in immune regulation lead to autoimmune diseases and of how the immune system could be better manipulated to overcome afflictions such as cancer, infection and autoimmune diseases [16, 17].

Data

Thermo Fisher Scientific offers antibodies, ELISAs, Invitrogen™ Luminex™ multiplex assays and growth factors for key targets in the TCR signaling pathway.

Featured below is flow cytometry, western blot, and immunohistochemistry data using Thermo Scientific™ products.

T-Cell Receptor (TCR) Overview - US (1)

Flow cytometry analysis of TCR V alpha 12.1 in Jurkat cells (green) compared to an isotype control (blue). Cells were harvested, adjusted to a concentration of 1-5x10^6 cells/mL, fixed with 2% paraformaldehyde and washed with PBS. Cells were blocked with a 2% solution of BSA-PBS for 30 minutes at room temperature and incubated with a TCR V alpha 12.1 monoclonal antibody (Product # TCR1764) at a dilution of 2 µg/test for 60 minutes at room temperature. Cells were then incubated for 40 minutes at room temperature in the dark using a Thermo Scientific™ Dylight™ 488–conjugated goat anti-mouse IgG (H+L) secondary antibody and re-suspended in PBS for FACS analysis.

T-Cell Receptor (TCR) Overview - US (2)

Western blot analysis of TCR V delta 2 was performed by loading 25 µg of Jurkat (lane 1) and CEM (lane 2) cell lysates onto an SDS polyacrylamide gel. Proteins were transferred to a PVDF membrane and blocked at 4°C overnight. The membrane was probed with a TCR V delta 2 monoclonal antibody (Product # TCR1732) at a dilution of 1:10 overnight at 4°C, washed in TBST, and probed with an HRP-conjugated secondary antibody for 1 hour at room temperature in the dark. Chemiluminescent detection was performed using Thermo Scientific™ Pierce™ ECL Plus Western Blotting Substrate (Product # 32132). Results show a band at ~19 kDa.

T-Cell Receptor (TCR) Overview - US (3)

Immunohistochemistry analysis of TCR Alpha F1 showing staining in the cytoplasm of paraffin-treated human tonsil tissue (right) compared with a negative control in the absence of primary antibody (left). To expose target proteins, antigen retrieval was performed using 10mM sodium citrate (pH 6.0), microwaved for 8-15 minutes. Following antigen retrieval, tissues were blocked in 3% H2O2-methanol for 15 minutes at room temperature, washed with ddH2O and PBS, and then probed with a TCR Alpha F1 monoclonal antibody (Product # TCR1145) diluted by 3% BSA-PBS at a dilution of 1:20 overnight at 4°C in a humidified chamber. Tissues were washed extensively in PBST and detection was performed using an HRP-conjugated secondary antibody followed by colorimetric detection using a DAB kit. Tissues were counterstained with hematoxylin and dehydrated with ethanol and xylene to prep for mounting.

Technical Resources

Thermo Fisher Scientific scientists have been hard at work trying to better understand the TCR cell signaling pathway over the years. For further information on this pathway please see our publication:

Publication: Putting Regulatory T Cells to Work

References

  1. Lin J, Weiss A. (2001) T cell receptor signaling. J Cell Sci. 114: 243-4.
  2. Okkenhaug K, Bilancio A, et al. (2004) Phosphoinositide 3-kinase in T cell activation and survival. Biochem Soc Trans. 32: 332-5.
  3. Davis MM. (2002) A new trigger for T cells. Cell 110(3): 285-7.
  4. Coombs D, Kalergis AM, et al. (2002) Activated TCRs remain marked for internalization after dissociation from pMHC. Nature Immunology 10: 926-31.
  5. Okkenhaug K, Vanhaesebroeck B. (2003) PI3K in lymphocyte development, differentiation and activation.
  6. Nat Rev Immunol. 3(4): 317-30.
  7. Gong Q, Cheng AM, et al. (2001) Disruption of T cell signaling networks and development by Grb2 haploid insufficiency. Nat Immunol 2(1): 29-36.
  8. Davidson D, Bakinowski M, et al. (2003) Phosphorylation-dependent regulation of T-cell activation by PAG/Cbp,a lipid raft-associated transmembrane adaptor. Mol Cell Biol. 23(6): 2017-28.
  9. Alonso A, Rahmouni S, et al (2002) Tyrosine phosphorylation of VHR phosphatase by ZAP-70. Nat Immunol. 4(1):44-8.
  10. Pomerantz JL, Denny EM, et al (2002). CARD11 mediates factor-specific activation of NF-kappaB by the T cell receptor complex. EMBO J 21(19):5184-94.
  11. Hara H, Wada T, et al. (2003) The MAGUK family protein CARD11 is essential for lymphocyte activation. Immunity 18(6):763-75.
  12. Wang D, You Y, et al. (2002). A requirement for CARMA1 in TCR-induced NF-kappa B activation. Nat Immunol 3(9): 830-5.
  13. Arndt, B., et al. (2011) The transmembrane adaptor protein SIT inhibits TCR-mediated signaling. PLoS ONE 6: e23761.
  14. Simeoni L, Posevitz V, et al. (2005) The transmembrane adapter protein SIT regulates thymic development and peripheral T-cell functions. Mol Cell Biol 25(17):7557-68.
  15. Gough SC, Walker LS, et al. (2005) CTLA4 gene polymorphism and autoimmunity. Immunol Rev 204:102-15.
  16. Krummey, S.M. & Ford, M.L. (2014) Braking bad: novel mechanisms of CTLA4 inhibition of T cell responses. American Journal of Transplantation 14: 2685-2690.
  17. Anderton SM. (2006) Avoiding autoimmune disease - T cells know their limits. Trends Immunol 27(5):208-14. Epub 2006 Mar 30.

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T-Cell Receptor (TCR) Overview - US (2024)

FAQs

What is the overview of T cell receptors? ›

T CELL RECEPTORS

The T cell receptor (TCR) is a T cell surface structure that is comprised of a disulfide-linked heterodimer of highly variable α and β chains expressed at the cell membrane as a complex with the invariant CD3 chains.

What is the TCR of the T cells? ›

The TCR (T-cell receptor) is a complex of integral membrane proteins that participate in the activation of T-cells in response to an antigen. Stimulation of TCR is triggered by MHC (major histocompatibility complex) molecules on cells with the antigen.

What does the T-cell receptor TCR complex contain? ›

The T-cell receptor (TCR)–CD3 complex is composed of a diverse αβ TCR heterodimer noncovalently associated with the invariant CD3 dimers CD3ϵγ, CD3ϵδ, and CD3ζζ. The TCR mediates recognition of antigenic peptides bound to MHC molecules (pMHC), whereas the CD3 molecules transduce activation signals to the T cell.

What happens when TCR is activated? ›

TCR signaling, in cooperation with signaling pathways induced by cytokines, costimulatory molecules, chemokines, integrins, and metabolites, drives the differentiation of activated T cells into specific T cell subtypes1. This results in the generation of various types of T cells with different specialized functions.

What does TCR sequencing tell you? ›

The T cell receptor (TCR) can act as a molecular barcode in mice and humans to track T cells with clonal-relatedness through processes such as migration, differentiation, and proliferation. The TCR sequence provides a means to enrich T cells of interest in diverse types of cancer and some types of autoimmunity.

How does TCR therapy work? ›

Exploiting the T-cell receptor in cancer treatment

The MHC is a complex which collects and presents protein fragments (peptides), including those found within cancer cells, to the TCR, thereby activating T cells and stimulating an immune response.

What does TCR bind to? ›

The T-cell receptor binds to the MHC:peptide complex.

What is the function of the TCR in immunology? ›

A TCR is a heterodimer composed of an alpha and a beta chain, or in a minor population (in humans), a gamma chain and a delta chain, and is responsible for the recognition of antigenic peptides presented at the surface of infected cells by major histocompatibility complex (MHC) molecules.

What is the most common T-cell receptor? ›

In humans, in 95% of T cells the TCR consists of an alpha (α) chain and a beta (β) chain (encoded by TRA and TRB, respectively), whereas in 5% of T cells the TCR consists of gamma and delta (γ/δ) chains (encoded by TRG and TRD, respectively). This ratio changes during ontogeny and in diseased states (such as leukemia).

How long does it take for T cells to activate? ›

Whereas naive T cells require approximately 20 hr of sustained signaling to be committed to proliferation, effector T cells become committed after only 1 hr but die following activation if antigenic stimulation is prolonged.

What triggers T cell activation? ›

In order to be activated, a naive T cell must recognize a foreign peptide bound to a self MHC molecule. But this is not, on its own, sufficient for activation. That requires the simultaneous delivery of a co-stimulatory signal by a specialized antigen-presenting cell.

How do you activate T cell receptors? ›

Naïve T cells require at least two signals for activation. Both are provided by an antigen-presenting cell, which is usually a dendritic cell: signal 1 is provided by MHC-peptide complexes binding to T cell receptors, while signal 2 is mainly provided by B7 costimulatory proteins binding to CD28 on the T cell surface.

What characterizes T cell receptors? ›

Unlike B cells, conventional T cells recognize antigen in the form of short peptide sequences associated with major histocompatibility complex (MHC) molecules on the surface of antigen presenting cells (APCs). T cells can be broadly characterized based on the expression of either CD4 or CD8 coreceptors.

What is the functional T-cell receptor? ›

A TCR is a heterodimer composed of an alpha and a beta chain, or in a minor population (in humans), a gamma chain and a delta chain, and is responsible for the recognition of antigenic peptides presented at the surface of infected cells by major histocompatibility complex (MHC) molecules.

What is the function of the T cell? ›

T cells are part of the immune system and develop from stem cells in the bone marrow. They help protect the body from infection and may help fight cancer. Also called T lymphocyte and thymocyte. Blood cell development.

What do T cell receptors recognize and bind to? ›

However, the T-cell receptor differs from the B-cell receptor in an important way: it does not recognize and bind antigen directly, but instead recognizes short peptide fragments of pathogen protein antigens, which are bound to MHC molecules on the surfaces of other cells.

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