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Kinetics and extent of T cell activation as measured with the calcium signal.

Wülfing C, Rabinowitz JD, Beeson C, Sjaastad MD, McConnell HM, Davis MM - J. Exp. Med. (1997)

Bottom Line: Whereas all three antagonist peptides tested reduce the calcium response to an agonist ligand, two give very different calcium release patterns and the third gives none at all, arguing that (a) antagonism does not require calcium release and (b) it involves interactions that are more T cell receptor proximal.The duration of this delay correlates with the strength of the stimulus, with stronger stimuli giving a more rapid response.The dose dependence of this delay suggests that the rate-limiting step in triggering the calcium response is not the clustering of peptide-MHC complexes on the cell surface but more likely involves the accumulation of some intracellular molecule or complex with a half-life of a few minutes.

View Article: PubMed Central - PubMed

Affiliation: Department of Microbiology and Immunology, Stanford University School of Medicine, Stanford, California 94305-5402, USA.

ABSTRACT
We have characterized the calcium response of a peptide-major histocompatibility complex (MHC)-specific CD4(+) T lymphocyte line at the single cell level using a variety of ligands, alone and in combination. We are able to distinguish four general patterns of intracellular calcium elevation, with only the most robust correlating with T cell proliferation. Whereas all three antagonist peptides tested reduce the calcium response to an agonist ligand, two give very different calcium release patterns and the third gives none at all, arguing that (a) antagonism does not require calcium release and (b) it involves interactions that are more T cell receptor proximal. We have also measured the time between the first T cell-antigen-presenting cell contact and the onset of the calcium signal. The duration of this delay correlates with the strength of the stimulus, with stronger stimuli giving a more rapid response. The dose dependence of this delay suggests that the rate-limiting step in triggering the calcium response is not the clustering of peptide-MHC complexes on the cell surface but more likely involves the accumulation of some intracellular molecule or complex with a half-life of a few minutes.

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Model of onset effect. The figure represents the accumulation of the critical signaling component B that has to reach the trigger  concentration Btr to induce the calcium response. The mathematics of the  model is given in the Materials and Methods section. Graphs for different  values of the rate constants k1 and k−1 are shown. k−1 is set to 1 in all  graphs to represent a constant removal of B. The postulated trigger to be  reached for the induction of the calcium signal is the production of the  half-maximal amount of B. The rate of formation of B, k1, is varied in the  three panels. It varies between 7.5 and 15 for A, as to represent the fast  formation of the signaling intermediate under different concentrations of  the agonist peptide, MCC. No onset delay is seen. k1 is set to values between 2 and 7.5 in B to represent the postulated formation of the signaling intermediate by different concentrations of the partial agonist, 102S.  The formation of B is not much faster than its removal. This results in a  strong onset effect. In C, the rate formation of B is 0.9. Because the rate  of formation is smaller than the rate of removal, the trigger concentration  is never reached on average, as to represent the antagonist peptide, 102G.
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Figure 7: Model of onset effect. The figure represents the accumulation of the critical signaling component B that has to reach the trigger concentration Btr to induce the calcium response. The mathematics of the model is given in the Materials and Methods section. Graphs for different values of the rate constants k1 and k−1 are shown. k−1 is set to 1 in all graphs to represent a constant removal of B. The postulated trigger to be reached for the induction of the calcium signal is the production of the half-maximal amount of B. The rate of formation of B, k1, is varied in the three panels. It varies between 7.5 and 15 for A, as to represent the fast formation of the signaling intermediate under different concentrations of the agonist peptide, MCC. No onset delay is seen. k1 is set to values between 2 and 7.5 in B to represent the postulated formation of the signaling intermediate by different concentrations of the partial agonist, 102S. The formation of B is not much faster than its removal. This results in a strong onset effect. In C, the rate formation of B is 0.9. Because the rate of formation is smaller than the rate of removal, the trigger concentration is never reached on average, as to represent the antagonist peptide, 102G.

Mentions: Instead, we suggest that the rate-limiting factor in this delay reflects intracellular reactions leading to the accumulation of signaling molecules. These reactions could involve a continuous competition between phosphorylation and dephosphorylation, or between production or breakdown of other parts of the signaling machinery. We hypothesize that T cell activation shifts the balance of this equilibrium towards the accumulation of signaling molecules. A simple kinetic model based on a reaction scheme of this type agrees well with the onset delay that we observe (Fig. 7). The crucial feature of this scheme is that the turnover of the rate-limiting signaling intermediate is determined by an activation strength-dependent first-order forward and an activation strength independent first-order reverse reaction:


Kinetics and extent of T cell activation as measured with the calcium signal.

Wülfing C, Rabinowitz JD, Beeson C, Sjaastad MD, McConnell HM, Davis MM - J. Exp. Med. (1997)

Model of onset effect. The figure represents the accumulation of the critical signaling component B that has to reach the trigger  concentration Btr to induce the calcium response. The mathematics of the  model is given in the Materials and Methods section. Graphs for different  values of the rate constants k1 and k−1 are shown. k−1 is set to 1 in all  graphs to represent a constant removal of B. The postulated trigger to be  reached for the induction of the calcium signal is the production of the  half-maximal amount of B. The rate of formation of B, k1, is varied in the  three panels. It varies between 7.5 and 15 for A, as to represent the fast  formation of the signaling intermediate under different concentrations of  the agonist peptide, MCC. No onset delay is seen. k1 is set to values between 2 and 7.5 in B to represent the postulated formation of the signaling intermediate by different concentrations of the partial agonist, 102S.  The formation of B is not much faster than its removal. This results in a  strong onset effect. In C, the rate formation of B is 0.9. Because the rate  of formation is smaller than the rate of removal, the trigger concentration  is never reached on average, as to represent the antagonist peptide, 102G.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2196319&req=5

Figure 7: Model of onset effect. The figure represents the accumulation of the critical signaling component B that has to reach the trigger concentration Btr to induce the calcium response. The mathematics of the model is given in the Materials and Methods section. Graphs for different values of the rate constants k1 and k−1 are shown. k−1 is set to 1 in all graphs to represent a constant removal of B. The postulated trigger to be reached for the induction of the calcium signal is the production of the half-maximal amount of B. The rate of formation of B, k1, is varied in the three panels. It varies between 7.5 and 15 for A, as to represent the fast formation of the signaling intermediate under different concentrations of the agonist peptide, MCC. No onset delay is seen. k1 is set to values between 2 and 7.5 in B to represent the postulated formation of the signaling intermediate by different concentrations of the partial agonist, 102S. The formation of B is not much faster than its removal. This results in a strong onset effect. In C, the rate formation of B is 0.9. Because the rate of formation is smaller than the rate of removal, the trigger concentration is never reached on average, as to represent the antagonist peptide, 102G.
Mentions: Instead, we suggest that the rate-limiting factor in this delay reflects intracellular reactions leading to the accumulation of signaling molecules. These reactions could involve a continuous competition between phosphorylation and dephosphorylation, or between production or breakdown of other parts of the signaling machinery. We hypothesize that T cell activation shifts the balance of this equilibrium towards the accumulation of signaling molecules. A simple kinetic model based on a reaction scheme of this type agrees well with the onset delay that we observe (Fig. 7). The crucial feature of this scheme is that the turnover of the rate-limiting signaling intermediate is determined by an activation strength-dependent first-order forward and an activation strength independent first-order reverse reaction:

Bottom Line: Whereas all three antagonist peptides tested reduce the calcium response to an agonist ligand, two give very different calcium release patterns and the third gives none at all, arguing that (a) antagonism does not require calcium release and (b) it involves interactions that are more T cell receptor proximal.The duration of this delay correlates with the strength of the stimulus, with stronger stimuli giving a more rapid response.The dose dependence of this delay suggests that the rate-limiting step in triggering the calcium response is not the clustering of peptide-MHC complexes on the cell surface but more likely involves the accumulation of some intracellular molecule or complex with a half-life of a few minutes.

View Article: PubMed Central - PubMed

Affiliation: Department of Microbiology and Immunology, Stanford University School of Medicine, Stanford, California 94305-5402, USA.

ABSTRACT
We have characterized the calcium response of a peptide-major histocompatibility complex (MHC)-specific CD4(+) T lymphocyte line at the single cell level using a variety of ligands, alone and in combination. We are able to distinguish four general patterns of intracellular calcium elevation, with only the most robust correlating with T cell proliferation. Whereas all three antagonist peptides tested reduce the calcium response to an agonist ligand, two give very different calcium release patterns and the third gives none at all, arguing that (a) antagonism does not require calcium release and (b) it involves interactions that are more T cell receptor proximal. We have also measured the time between the first T cell-antigen-presenting cell contact and the onset of the calcium signal. The duration of this delay correlates with the strength of the stimulus, with stronger stimuli giving a more rapid response. The dose dependence of this delay suggests that the rate-limiting step in triggering the calcium response is not the clustering of peptide-MHC complexes on the cell surface but more likely involves the accumulation of some intracellular molecule or complex with a half-life of a few minutes.

Show MeSH
Related in: MedlinePlus