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Recognition of the major histocompatibility complex restriction element modulates CD8(+) T cell specificity and compensates for loss of T cell receptor contacts with the specific peptide.

Sandberg JK, Kärre K, Glas R - J. Exp. Med. (1999)

Bottom Line: Furthermore, recognition of the restriction element at expression levels below this threshold was still enough to compensate for lack of affinity to peptides carrying alanine substitutions in major TCR contact residues.Thus, the specificity in TCR recognition and T cell activation is fine tuned by the avidity for self-MHC, and TCR avidities for peptide and MHC may substitute for each other.These results demonstrate a functional role for TCR avidity for self-MHC in tuning of T cell specificity, and support a role for cross-reactivity on "self" during T cell selection and activation.

View Article: PubMed Central - PubMed

Affiliation: Microbiology and Tumor Biology Center, Karolinska Institute, S-17177 Stockholm, Sweden.

ABSTRACT
Triggering of a T cell requires interaction between its specific receptor (TCR) and a peptide antigen presented by a self-major histocompatibility complex (MHC) molecule. TCR recognition of self-MHC by itself falls below the threshold of detection in most systems due to low affinity. To study this interaction, we have used a read-out system in which antigen-specific effector T cells are confronted with targets expressing high levels of MHC compared with the selecting and priming environment. More specifically, the system is based on CD8(+) T cells selected in an environment with subnormal levels of MHC class I in the absence of beta2-microglobulin. We observe that the MHC restriction element can trigger viral peptide-specific T cells independently of the peptide ligand, provided there is an increase in self-MHC density. Peptide-independent triggering required at least four times the natural in vivo level of MHC expression. Furthermore, recognition of the restriction element at expression levels below this threshold was still enough to compensate for lack of affinity to peptides carrying alanine substitutions in major TCR contact residues. Thus, the specificity in TCR recognition and T cell activation is fine tuned by the avidity for self-MHC, and TCR avidities for peptide and MHC may substitute for each other. These results demonstrate a functional role for TCR avidity for self-MHC in tuning of T cell specificity, and support a role for cross-reactivity on "self" during T cell selection and activation.

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CTL triggering by self-MHC is a low-avidity event that requires interaction with a high density of ligands. (A) Recognition by β2m−/−  LCMV GP33-specific polyclonal CTLs of RMA in the absence or presence of GP33 peptide was blocked using the anti–H-2Db conformation-specific  mAb B22-249.1. (B) FACS® analysis of B22-249.1 titration on RMA cells. (C) Recognition by the GP33-specific β2m−/− CTL clone 27/30 of T2Db  loaded with GP33, Yop249, NP366, or T2Db without peptide was blocked using B22-249.1. (D) FACS® analysis of B22-249.1 titration on T2Db. The  preincubation of target cells with peptide at 37°C did not affect expression of H-2Db in these experiments (data not shown).
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Figure 5: CTL triggering by self-MHC is a low-avidity event that requires interaction with a high density of ligands. (A) Recognition by β2m−/− LCMV GP33-specific polyclonal CTLs of RMA in the absence or presence of GP33 peptide was blocked using the anti–H-2Db conformation-specific mAb B22-249.1. (B) FACS® analysis of B22-249.1 titration on RMA cells. (C) Recognition by the GP33-specific β2m−/− CTL clone 27/30 of T2Db loaded with GP33, Yop249, NP366, or T2Db without peptide was blocked using B22-249.1. (D) FACS® analysis of B22-249.1 titration on T2Db. The preincubation of target cells with peptide at 37°C did not affect expression of H-2Db in these experiments (data not shown).

Mentions: We next compared the avidity of β2m−/− CTLs for self-MHC with and without added GP33, by blocking of the H-2Db ligands. We used an mAb specific for properly conformed H-2Db molecules (B22-249.1), the binding of which is not affected by GP33 (data not shown). RMA target cells were killed at similar levels regardless of the presence or absence of specific peptide (Fig. 5). However, in the absence of GP33 peptide the CTL killing activity was efficiently blocked by 5.0 μg/ml of B22-249.1, whereas virtually no blocking was observed when the RMA target cells were prepulsed with the GP33 peptide at 37°C (Fig. 5 A). FACS® analysis of B22-249.1 binding to RMA cells did not allow accurate quantitation of the fraction of free H-2Db ligands at half-maximal lysis, since half-maximal blocking of CTL lysis was achieved at a concentration at which staining was close to maximal (Fig. 5 B). However, these experiments clearly demonstrate that triggering of β2m−/− CTLs in the absence of GP33 peptide requires a considerably higher number of H-2Db ligands.


Recognition of the major histocompatibility complex restriction element modulates CD8(+) T cell specificity and compensates for loss of T cell receptor contacts with the specific peptide.

Sandberg JK, Kärre K, Glas R - J. Exp. Med. (1999)

CTL triggering by self-MHC is a low-avidity event that requires interaction with a high density of ligands. (A) Recognition by β2m−/−  LCMV GP33-specific polyclonal CTLs of RMA in the absence or presence of GP33 peptide was blocked using the anti–H-2Db conformation-specific  mAb B22-249.1. (B) FACS® analysis of B22-249.1 titration on RMA cells. (C) Recognition by the GP33-specific β2m−/− CTL clone 27/30 of T2Db  loaded with GP33, Yop249, NP366, or T2Db without peptide was blocked using B22-249.1. (D) FACS® analysis of B22-249.1 titration on T2Db. The  preincubation of target cells with peptide at 37°C did not affect expression of H-2Db in these experiments (data not shown).
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Figure 5: CTL triggering by self-MHC is a low-avidity event that requires interaction with a high density of ligands. (A) Recognition by β2m−/− LCMV GP33-specific polyclonal CTLs of RMA in the absence or presence of GP33 peptide was blocked using the anti–H-2Db conformation-specific mAb B22-249.1. (B) FACS® analysis of B22-249.1 titration on RMA cells. (C) Recognition by the GP33-specific β2m−/− CTL clone 27/30 of T2Db loaded with GP33, Yop249, NP366, or T2Db without peptide was blocked using B22-249.1. (D) FACS® analysis of B22-249.1 titration on T2Db. The preincubation of target cells with peptide at 37°C did not affect expression of H-2Db in these experiments (data not shown).
Mentions: We next compared the avidity of β2m−/− CTLs for self-MHC with and without added GP33, by blocking of the H-2Db ligands. We used an mAb specific for properly conformed H-2Db molecules (B22-249.1), the binding of which is not affected by GP33 (data not shown). RMA target cells were killed at similar levels regardless of the presence or absence of specific peptide (Fig. 5). However, in the absence of GP33 peptide the CTL killing activity was efficiently blocked by 5.0 μg/ml of B22-249.1, whereas virtually no blocking was observed when the RMA target cells were prepulsed with the GP33 peptide at 37°C (Fig. 5 A). FACS® analysis of B22-249.1 binding to RMA cells did not allow accurate quantitation of the fraction of free H-2Db ligands at half-maximal lysis, since half-maximal blocking of CTL lysis was achieved at a concentration at which staining was close to maximal (Fig. 5 B). However, these experiments clearly demonstrate that triggering of β2m−/− CTLs in the absence of GP33 peptide requires a considerably higher number of H-2Db ligands.

Bottom Line: Furthermore, recognition of the restriction element at expression levels below this threshold was still enough to compensate for lack of affinity to peptides carrying alanine substitutions in major TCR contact residues.Thus, the specificity in TCR recognition and T cell activation is fine tuned by the avidity for self-MHC, and TCR avidities for peptide and MHC may substitute for each other.These results demonstrate a functional role for TCR avidity for self-MHC in tuning of T cell specificity, and support a role for cross-reactivity on "self" during T cell selection and activation.

View Article: PubMed Central - PubMed

Affiliation: Microbiology and Tumor Biology Center, Karolinska Institute, S-17177 Stockholm, Sweden.

ABSTRACT
Triggering of a T cell requires interaction between its specific receptor (TCR) and a peptide antigen presented by a self-major histocompatibility complex (MHC) molecule. TCR recognition of self-MHC by itself falls below the threshold of detection in most systems due to low affinity. To study this interaction, we have used a read-out system in which antigen-specific effector T cells are confronted with targets expressing high levels of MHC compared with the selecting and priming environment. More specifically, the system is based on CD8(+) T cells selected in an environment with subnormal levels of MHC class I in the absence of beta2-microglobulin. We observe that the MHC restriction element can trigger viral peptide-specific T cells independently of the peptide ligand, provided there is an increase in self-MHC density. Peptide-independent triggering required at least four times the natural in vivo level of MHC expression. Furthermore, recognition of the restriction element at expression levels below this threshold was still enough to compensate for lack of affinity to peptides carrying alanine substitutions in major TCR contact residues. Thus, the specificity in TCR recognition and T cell activation is fine tuned by the avidity for self-MHC, and TCR avidities for peptide and MHC may substitute for each other. These results demonstrate a functional role for TCR avidity for self-MHC in tuning of T cell specificity, and support a role for cross-reactivity on "self" during T cell selection and activation.

Show MeSH
Related in: MedlinePlus