Coreceptor Scanning by the T Cell Receptor Provides a Mechanism for T Cell Tolerance

How T cells become restricted to binding antigenic peptides within class I or class II major histocompatibility complex molecules (pMHCI or pMHCII, respectively) via clonotypic T-cell receptors (TCRs) remains debated. During development, if TCR-pMHC interactions exceed an affinity threshold, a signal is generated that positively selects the thymocyte to become a mature CD4 + or CD8 + T cell that can recognize foreign peptides within MHCII or MHCI, respectively. But whether TCRs possess an intrinsic, subthreshold specificity for MHC that facilitates sampling of the peptides within MHC during positive selection or T-cell activation is undefined. Here we asked if increasing the frequency of lymphocyte-specific protein tyrosine kinase (Lck)-associated CD4 molecules in T-cell hybridomas would allow for the detection of subthreshold TCR-MHC interactions. The reactivity of 10 distinct TCRs was assessed in response to selecting and nonselecting MHCII bearing cognate, null, or "shaved" peptides with alanine substitutions at known TCR contact residues: Three of the TCRs were selected on MHCII and have defined peptide specificity, two were selected on MHCI and have a known pMHC specificity, and five were generated in vitro without defined selecting or cognate pMHC. Our central finding is that IL-2 was made when each TCR interacted with selecting or nonselecting MHCII presenting shaved peptides. These responses were abrogated by anti-CD4 antibodies and mutagenesis of CD4. They were also inhibited by anti-MHC antibodies that block TCR-MHCII interactions. We interpret these data as functional evidence for TCR-intrinsic specificity for MHCII.TCR | MHC | restriction | CD4 | Lck P ositive and negative selection limit the αβT-cell repertoire to cells expressing clonotypic T-cell receptors (TCRs) that distinguish the antigenicity of peptides embedded within class I and class II major histocompatibility complex molecules (pMHCI or pMHCII, respectively) based on their source of origin (i.e., self or foreign) (1-4). Approximately 7.5% of CD4 + CD8+ doublepositive (DP) thymocytes express TCRs that interact with selfpMHC above an affinity threshold required for positive selection, whereas 7.5% cross a higher affinity threshold that mediates negative selection and the remaining TCRs fail to direct positive selection (5). The rules that restrict TCR recognition of antigenic peptides within MHCI or MHCII are unresolved.Two models have been proposed to explain MHC restriction. One posits that restriction is imposed by CD4 or CD8 during thymocyte development to eliminate TCRs that recognize non-MHC ligands (2, 6). Here, the CD4-and CD8-associated Src kinase, p56Lck [lymphocyte-specific protein tyrosine kinase (Lck)], is sequestered away from the immunoreceptor tyrosine-based activation motifs (ITAMs) of the TCR-associated CD3δe, CD3γe, and CD3ζζ signaling modules. Positively selecting signals are then generated in thymocytes expressing TCRs that bind MHCII or MHCI together with CD4 or CD8, respectively, as this localizes Lck to the ITAMs. T...

Section: Resultssupporting

confidence: 57%

Section: Resultsmentioning

confidence: 99%

Section: Significancementioning

confidence: 99%

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Functional evidence for TCR-intrinsic specificity for MHCII

Parrish

Deshpande

Vasic

et al. 2016

“…Importantly, these ligands have equivalent binding to H-2A b but differ in their ability to stimulate B3K508 TCR transgenic T cells (24,26). The thymic selection potential of 3K and its variants was recently assessed using fetal thymic organ culture (27). The ligands 3K, P5R, and P2A induced strong negative selection of developing B3K508 thymocytes, while the ligand P-1A elicited only partial thymocyte deletion (Fig.…”

Section: Resultsmentioning

confidence: 99%

Antigen affinity and antigen dose exert distinct influences on CD4 T-cell differentiation

Keck

Schmaler

Ganter

et al. 2014

110

107

Cumulative T-cell receptor signal strength and ensuing T-cell responses are affected by both antigen affinity and antigen dose. Here we examined the distinct contributions of these parameters to CD4 T-cell differentiation during infection. We found that high antigen affinity positively correlates with T helper (Th)1 differentiation at both high and low doses of antigen. In contrast, follicular helper T cell (T FH ) effectors are generated after priming with high, intermediate, and low affinity ligand. Unexpectedly, memory T cells generated after priming with very low affinity antigen remain impaired in their ability to generate secondary Th1 effectors, despite being recalled with high affinity antigen. These data challenge the view that only strongly stimulated CD4 T cells are capable of differentiating into the T FH and memory T-cell compartments and reveal that differential strength of stimulation during primary T-cell activation imprints unique and long lasting T-cell differentiation programs.follicular helper | infection | lymphocytes

“…Experimental removal of Lck by genetic manipulation is a useful tool to probe signals downstream of the TCR and will mimic the status of aging lymphocytes that lose expression of Lck (21,22). In Lck-sufficient T cells, Lck activation upon TCR binding can be influenced also by the extent and duration of coreceptor recruitment, which happens when T cells are stimulated by altered peptide ligands with low affinities (23)(24)(25). A consequence of stimulation by altered peptide ligands is that the expansion potential of T cells is curtailed compared with that induced by strong agonist ligands (3).…”

Section: Weak Alternate Peptide Ligands Stimulate Ribosome Biogenesismentioning

confidence: 99%

Suboptimal T-cell receptor signaling compromises protein translation, ribosome biogenesis, and proliferation of mouse CD8 T cells

Tan

Knight

Sbarrato

et al. 2017

Global transcriptomic and proteomic analyses of T cells have been rich sources of unbiased data for understanding T-cell activation. Lack of full concordance of these datasets has illustrated that important facets of T-cell activation are controlled at the level of translation. We undertook translatome analysis of CD8 T-cell activation, combining polysome profiling and microarray analysis. We revealed that altering T-cell receptor stimulation influenced recruitment of mRNAs to heavy polysomes and translation of subsets of genes. A major pathway that was compromised, when TCR signaling was suboptimal, was linked to ribosome biogenesis, a rate-limiting factor in both cell growth and proliferation. Defective TCR signaling affected transcription and processing of ribosomal RNA precursors, as well as the translation of specific ribosomal proteins and translation factors. Mechanistically, IL-2 production was compromised in weakly stimulated T cells, affecting the abundance of Myc protein, a known regulator of ribosome biogenesis. Consequently, weakly activated T cells showed impaired production of ribosomes and a failure to maintain proliferative capacity after stimulation. We demonstrate that primary T cells respond to various environmental cues by regulating ribosome biogenesis and mRNA translation at multiple levels to sustain proliferation and differentiation.