Serial Triggering of T Cell Receptors Results in Incremental Accumulation of Signaling Intermediates

Abstract

Triggering of the T cell receptor (TCR) leads to the production of intracellular intermediates with half-life of a few minutes. Signaling kinetics of events originating from serial TCR triggering and its relation to antigen dose was investigated. In this study we documented incremental accumulation of short-lived intermediates of the extracellular signal-regulated kinase (ERK) family, produced during successive TCR triggering. The rate and extent of the intermediate accumulation are essentially determined by the level of TCR engagement and are augmented by costimulation. ERK-1 and ERK-2 exhibit different rates of accumulation following serial receptor triggering. The data indicate that the quantitative kinetic differences in downstream signaling pathways induce qualitatively distinct biological outcomes. Although CD69, interleukin-2, and interferon-␥ (IFN-␥) were primarily produced by high antigen doses that supported high MAPK phosphorylation, maximal interleukin-5 expression is induced by low and intermediate stimulus doses that do not support significant accumulation of activated ERK. We further demonstrated that the rate of phosphorylated ERK accumulation correlates with the duration of delay between T cell stimulation and the onset of IFN-␥ response, with stronger stimuli giving a more rapid IFN-␥ response. This delay might reflect the time required for the accumulation of signaling intermediates up to a threshold level that is necessary for activation. Thus, the data suggest that signaling events originating from serially triggered TCR are not simply sustained but are gradually accumulated and are integrated in a corresponding response.A single peptide antigen-major histocompatibility complex (MHC) 1 complex on the surface of an antigen-presenting cell (APC) can serially engage and trigger up to ϳ200 T cell receptors (TCRs) on a responding T cell (1). As a consequence of this "antigenic efficiency," relatively small numbers of peptide-MHC complexes on APC surfaces can trigger the threshold numbers of TCRs that are required for T cell activation (2).This intriguing feature of the T cell activation process makes physiological sense, in face of the antigenic complexity, as well as the consequent low frequency of any particular antigen, on the surface of any given APC in vivo.Any explanation of how serially receptor triggering leads to T cell activation must reconcile two opposing kinetic features. On the one hand, the signal emanating from each triggered TCR is short-lived and, in the absence of a continuous TCR triggering, the signal will stop. This point has been established by the demonstration that interference with continuous TCR engagement by peptide-MHC complexes can terminate signaling within minutes (3, 4). Furthermore, productive TCR engagement results in rapid TCR internalization and degradation (reviewed in Ref. 5). However, on the other hand, prolonged intracellular signaling over several hours is required for T cell activation (6).The intracellular signaling events underlying the serial trigge...

Differential Regulation of Th1/Th2 Cytokine Responses by Placental Protein 14

“…In contrast, the Th2 cytokine IL-5 approached its plateau at 1 ng/ml SEB, and further increases in the SEB dose enhanced cytokine secretion only marginally. This pattern of dose-dependent cytokine responses is consistent with earlier reports by us (26) and others (1,(27)(28)(29) for both SEB and other Ags. Of note, while the absolute levels of cytokine secretion varied up to 10-fold between different donors, the same pattern was evident in each case.…”

“…Thus, while both Th1 and Th2 cytokines are expressed simultaneously, low doses of stimuli primarily induced Th2 cytokines (IL-4 and IL-5), with low to undetectable levels of Th1 cytokines (IL-2 and IFN-␥), whereas priming with higher doses of stimuli favored increased production of Th1 cytokines. The Th1 skewing was correlated with the induction of ERK phosphorylation (26), and blocking this phosphorylation event specifically blocks the Th1 response (38). The observed effects of PP14 on early cytokine output can be readily understood within this framework.…”

B-Raf Contributes to Sustained Extracellular Signal-regulated Kinase Activation Associated with Interleukin-2 Production Stimulated through the T Cell Receptor

“…5D). Such temporal differences in ERK activation have been reported, and the authors suggested that this phenomenon was due to the difference in TCR occupancy (42). As shown in Fig.…”

The SCHOOL of nature: I. Transmembrane signaling

“…There exist numerous models of TCR triggering and their modifications, 2 including, but not limited to, a kinetic proofreading model, 280,296,298,[302][303][304][305][306] serial triggering model, 162,[307][308][309][310] serial encounter model, 311 conformational models, 126,165,[193][194][195]258,[312][313][314][315][316][317][318][319] Figure 8 (See previous page). SCHOOL model of T cell receptor (TCr) signaling.…”