Clone-specific T cell receptor antagonists of major histocompatibility complex class I-restricted cytotoxic T cells.

Abstract

SlimmaryA previous report showed that the proliferative response of helper T cells to class II major histocompatibility complex (MHC)-restricted antigens can be inhibited by analogues of the antigen, which act as T cell receptor (TCR) antagonists. Here we define and analyze peptide variants that antagonize various functions of class I MHC-restricted cytotoxic T lymphocyte (CTL) clones. Of 64 variants at individual TCR contact sites of the Kb-restricted octamer peptide ovalbumin257-264 (OVAp), a very high proportion (40%) antagonized lysis by three OVApspecific CTL clones. This effect was highly clone specific, since many antagonists for one T cell clone have differential effects on another. We show that this inhibition of CTL function is not a result of T ceU-T cell interaction, precluding veto-like phenomena as a mechanism for antagonism. Moreover, we present evidence for direct interaction between the TCR and antagonist-MHC complexes. In further analysis of the T cell response, we found that serine esterase release and cytokine production are susceptible to TCR antagonism similarly to lysis. Ca 2+ flux, an early event in signaling, is also inhibited by antagonists but may be more resistant to the antagonist effect than downstream responses. For mature T cells, stimulation of the TCK by an appropriate peptide-MHC complex on an APC usually results in activation. However, recent data have demonstrated that certain variants of the antigenic peptide can inhibit the proliferative response of helper T cells to antigen (1). Those experiments showed that this effect was not due to blockade of the restricting MHC molecule by the variant peptide, a form of peptide inhibition that has been well described (2-4), and indicated that the peptide variants acted as TCR antagonists, i.e., interacted with the TCR without inducing a signal (1). Analogous results have been obtained by others showing that differential T cell signals may be obtained with mutated antigenic peptides (5). Together these data indicate that TCRs make a novel interaction with antagonist peptide-MHC complexes, which does not produce a typical signal. However, it is still unclear exactly what quantitative and qualitative differences distinguish the TCR interaction with agonist versus antagonist peptides. Furthermore, what signals (if any) result from antagonist-MHC interaction and how these translate into the T cell inhibition observed is unknown. Previous reports have focused on helper cell jproliferation (1, 5), but other steps in the signaling pathway nave not so far been analyzed for their sensitivity to antagonism.We wished to investigate the nature of the TCR. interaction with antagonist peptides and to explore the mechanism by which TCR antagonism inhibits T cell function. This report describes a large panel of TCR antagonists that inhibit CTL lysis in a clone-specific manner. Sensitivity to antagonist interaction was also analyzed for other T cell responses ranging from immediate to late activation events. Materials and MethodsCell Lines. The ovalbum...

Specificity and flexibility in thymic selection

“…Here we examine peptide fine specificity in positive selection. These data suggest that a direct TCR-peptide interaction occurs during this event, and strengthens the correlation between selecting peptides and TCR antagonists 9,10 . Certain positively selecting peptides are weakly antigenic 9 .…”

“…We previously showed that peptides that induce positive selection, including E1 and R4, also act as TCR antagonists 9,10 (Fig. 2).…”

“…Our results are hard to reconcile with the latter model; thus if both E1 and R4 simply keep out of the TCR's way, it is likely that E1R4 would do so too, and hence should positively select. Therefore, our data support a peptide interaction model.We previously showed that peptides that induce positive selection, including E1 and R4, also act as TCR antagonists 9,10 (Fig. 2).…”

“…2), demonstrating similar fine specificity for positive selection and TCR antagonism. This suggests that the two phenomena may have a similar mechanistic basis, possibly based on TCR affinity for the peptide-MHC ligand 9,10,17,18 . However, some peptides that are weak agonists induce positive selection at low concentrations and negative selection at higher concentrations ( refs 9, 19, 20 and K.A.H.…”

Stochastic effects and bistability in T cell receptor signaling

“…It is known that antagonist peptides (peptides with a binding time of a few seconds) not only are unable to activate T cells, but also inhibit agonist peptide activation (Racioppi et al, 1996;Jameson et al, 1993). According to our model this inhibition results from activation of negative feedback mediated by pSHP rather than competition for receptors or other signaling molecules.…”