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Quantitative contribution of CD4 and CD8 to T cell antigen receptor serial triggering.

Viola A, Salio M, Tuosto L, Linkert S, Acuto O, Lanzavecchia A - J. Exp. Med. (1997)

Bottom Line: This coordinated disappearance takes place whenever the TCR is triggered, even when the coreceptor does not engage the cognate MHC molecule and is the consequence of binding of the coreceptor-associated Lck to ZAP-70.The interaction of coreceptor and cognate MHC molecules is dispensable when T cells are stimulated by optimal ligands, but becomes crucial when suboptimal ligands are used.In the latter case the coreceptor increases the efficiency of TCR triggering without changing the activation threshold or the quality of the T cell response.

View Article: PubMed Central - PubMed

Affiliation: Basel Institute for Immunology, Switzerland. viola@bii.ch

ABSTRACT
CD4 and CD8 are thought to function as coreceptors by binding to the cognate major histocompatibility complex (MHC) molecules recognized by the T cell antigen receptor (TCR) and initiating the signal transduction cascade. We report that during T cell-antigen-presenting cell interaction, triggered TCRs and coreceptors are downregulated and degraded with identical kinetics. This coordinated disappearance takes place whenever the TCR is triggered, even when the coreceptor does not engage the cognate MHC molecule and is the consequence of binding of the coreceptor-associated Lck to ZAP-70. The interaction of coreceptor and cognate MHC molecules is dispensable when T cells are stimulated by optimal ligands, but becomes crucial when suboptimal ligands are used. In the latter case the coreceptor increases the efficiency of TCR triggering without changing the activation threshold or the quality of the T cell response.

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Intracellular association of coreceptor with triggered  TCRs. (A) T cell clones were  stimulated (+) or not (−) with  APCs, lysed, and the CD4 or  CD8 immunoprecipitates were  subjected to an in vitro kinase assay, followed by reimmunoprecipitation with anti–ZAP-70 antiserum. CD4+ clone KS140  conjugated with peptide-pulsed  or unpulsed APCs (lanes 1 and  2). CD8+ clone MS3 either untreated or conjugated with allogeneic class I− APC (lanes 3 and 4). (B)  Downregulation of CD3 (○, •) and CD4 (▵, ▴) in CD4− Jurkat cells  transfected with wild-type CD4 (▵, ○) or with mutant CD4.401 (▴, •).
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Figure 3: Intracellular association of coreceptor with triggered TCRs. (A) T cell clones were stimulated (+) or not (−) with APCs, lysed, and the CD4 or CD8 immunoprecipitates were subjected to an in vitro kinase assay, followed by reimmunoprecipitation with anti–ZAP-70 antiserum. CD4+ clone KS140 conjugated with peptide-pulsed or unpulsed APCs (lanes 1 and 2). CD8+ clone MS3 either untreated or conjugated with allogeneic class I− APC (lanes 3 and 4). (B) Downregulation of CD3 (○, •) and CD4 (▵, ▴) in CD4− Jurkat cells transfected with wild-type CD4 (▵, ○) or with mutant CD4.401 (▴, •).

Mentions: The mechanism responsible for the downregulation of the coreceptor was next investigated. Three lines of evidence indicate that the downregulation of the coreceptor was due to an intracellular association with triggered TCRs. First, immunoprecipitation experiments showed that, as previously demonstrated in Jurkat cells activated by anti-CD3 antibodies (19, 20), a complex-containing coreceptor, Lck and ZAP-70, is formed after T cell activation by a specific ligand (Fig. 3 A). Comparable results were obtained when the reimmunoprecipitation was performed with either anti–ZAP-70 or anti-ζ. Second, treatment with the Lck inhibitors genistein or herbimycin A does not interfere with TCR downregulation, but completely inhibits coreceptor downregulation (data not shown). Third, truncated CD4 molecules that fail to associate with Lck are not downregulated with triggered TCRs (Fig. 3 B).


Quantitative contribution of CD4 and CD8 to T cell antigen receptor serial triggering.

Viola A, Salio M, Tuosto L, Linkert S, Acuto O, Lanzavecchia A - J. Exp. Med. (1997)

Intracellular association of coreceptor with triggered  TCRs. (A) T cell clones were  stimulated (+) or not (−) with  APCs, lysed, and the CD4 or  CD8 immunoprecipitates were  subjected to an in vitro kinase assay, followed by reimmunoprecipitation with anti–ZAP-70 antiserum. CD4+ clone KS140  conjugated with peptide-pulsed  or unpulsed APCs (lanes 1 and  2). CD8+ clone MS3 either untreated or conjugated with allogeneic class I− APC (lanes 3 and 4). (B)  Downregulation of CD3 (○, •) and CD4 (▵, ▴) in CD4− Jurkat cells  transfected with wild-type CD4 (▵, ○) or with mutant CD4.401 (▴, •).
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Related In: Results  -  Collection

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Figure 3: Intracellular association of coreceptor with triggered TCRs. (A) T cell clones were stimulated (+) or not (−) with APCs, lysed, and the CD4 or CD8 immunoprecipitates were subjected to an in vitro kinase assay, followed by reimmunoprecipitation with anti–ZAP-70 antiserum. CD4+ clone KS140 conjugated with peptide-pulsed or unpulsed APCs (lanes 1 and 2). CD8+ clone MS3 either untreated or conjugated with allogeneic class I− APC (lanes 3 and 4). (B) Downregulation of CD3 (○, •) and CD4 (▵, ▴) in CD4− Jurkat cells transfected with wild-type CD4 (▵, ○) or with mutant CD4.401 (▴, •).
Mentions: The mechanism responsible for the downregulation of the coreceptor was next investigated. Three lines of evidence indicate that the downregulation of the coreceptor was due to an intracellular association with triggered TCRs. First, immunoprecipitation experiments showed that, as previously demonstrated in Jurkat cells activated by anti-CD3 antibodies (19, 20), a complex-containing coreceptor, Lck and ZAP-70, is formed after T cell activation by a specific ligand (Fig. 3 A). Comparable results were obtained when the reimmunoprecipitation was performed with either anti–ZAP-70 or anti-ζ. Second, treatment with the Lck inhibitors genistein or herbimycin A does not interfere with TCR downregulation, but completely inhibits coreceptor downregulation (data not shown). Third, truncated CD4 molecules that fail to associate with Lck are not downregulated with triggered TCRs (Fig. 3 B).

Bottom Line: This coordinated disappearance takes place whenever the TCR is triggered, even when the coreceptor does not engage the cognate MHC molecule and is the consequence of binding of the coreceptor-associated Lck to ZAP-70.The interaction of coreceptor and cognate MHC molecules is dispensable when T cells are stimulated by optimal ligands, but becomes crucial when suboptimal ligands are used.In the latter case the coreceptor increases the efficiency of TCR triggering without changing the activation threshold or the quality of the T cell response.

View Article: PubMed Central - PubMed

Affiliation: Basel Institute for Immunology, Switzerland. viola@bii.ch

ABSTRACT
CD4 and CD8 are thought to function as coreceptors by binding to the cognate major histocompatibility complex (MHC) molecules recognized by the T cell antigen receptor (TCR) and initiating the signal transduction cascade. We report that during T cell-antigen-presenting cell interaction, triggered TCRs and coreceptors are downregulated and degraded with identical kinetics. This coordinated disappearance takes place whenever the TCR is triggered, even when the coreceptor does not engage the cognate MHC molecule and is the consequence of binding of the coreceptor-associated Lck to ZAP-70. The interaction of coreceptor and cognate MHC molecules is dispensable when T cells are stimulated by optimal ligands, but becomes crucial when suboptimal ligands are used. In the latter case the coreceptor increases the efficiency of TCR triggering without changing the activation threshold or the quality of the T cell response.

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