A correlation between function and selected measures of T cell avidity in influenza virus‐specific CD8⁺ T cell responses

Abstract

Activation of mature CD8 + T cells requires recognition, via the T cell receptor (TCR), of peptide + MHC (pMHC) complexes with an avidity that exceeds a designated threshold. Multiple indicators of T cell avidity have been described that provide unique information on the characteristics of T cell interactions. However, these indicators are routinely used in isolation, and, consequently, little is known about correlations between these measures or which measure, if any, correlates with the quality of the T cell response. Following influenza virus infection of C57BL/6J mice, we analyzed the relative avidities of five epitope-specific CD8 + T cell populations using five different measures. We demonstrated that the quality of CD8 + T cell responses, in terms of cytokine profiles, correlates with TCR dissociation rate and CD8 dependence, but not with the sensitivity to tetramer binding or peptide stimulation. Thus, we propose that, despite significant differences in TCR dissociation rate, the stimulation threshold of influenza-specific CD8 + T cell populations may be equivalent due to compensatory mechanisms largely provided by the CD8 coreceptor. Furthermore, this study shows that different indicators of avidity do not necessarily provide similar information and should be used in combination to obtain an overall picture of the characteristics of TCR binding.Supporting information for this article is available at http://www.wiley-vch.de/contents/jc_2040/2006/36390_s.pdf IntroductionThe fate of a T cell depends heavily on the avidity of the TCR:peptide + MHC (pMHC) interaction (reviewed in [1,2]). The collective avidity, or total strength, of the T cell-APC interaction is determined both by the affinity of a single TCR for its pMHC complex and by the number of TCR-pMHC interactions and the contribution of accessory molecules, such as CD4 or CD8, which can also bind MHC molecules upon TCR engagement [3]. In the thymus, immature T cells die if they do not recognize self pMHC molecules with minimal avidity. Conversely, recognition of pMHC exceeding an upper limit of avidity results in negative selection during T cell development. For mature peripheral T cells, upper and lower avidity limits also exist; below a critical threshold T cells do not receive sufficient signal for activation, while studies have shown that too high an avidity also impairs T cell activation, presumably by reducing the ability of the TCR to dissociate from the pMHC complex, thereby impeding serial TCR engagement [4]. Between the upper and lower avidity thresholds, TCR engagement can result in the functional activation of T cells.The term "avidity" is broadly used to describe various distinct features of T cell-APC interactions, including dependence on coreceptors for stimulation, TCR dissociation rate, and thresholds of T cell binding and/or activation. Thus, while correlations have been made between increased T cell "avidity" and functional responsiveness of T cells [5][6][7][8], the definition of avidity is arbitrary and usually based on the meas...

Influenza Epitope-Specific CD8+ T Cell Avidity, but Not Cytokine Polyfunctionality, Can Be Determined by TCRβ Clonotype

“…This was particularly intriguing for the D b PA 224 -specific population, where we saw clear partitioning of clonotypes in the highavidity subset, and suggests that polyfunctionality (at least for this epitope) is not a selective characteristic of the high-avidity population. This is supported by one study (15) in which polyfunctionality correlated more closely with the HLA restriction element and was inversely correlated with avidity, but contrasts with a number of other studies (including our own) that have indicated a link between the strength of the TCR-pMHCI interaction and the propensity to produce multiple cytokines (6,7,13,14,19). Critically, however, the nexus between avidity and polyfunctionality in the majority of these studies was correlative, leaving open the possibility that these two effects segregate independently.…”

“…Although the restriction of our analyses to the contribution of TCRb-chain to differential avidity and polyfunctionality precludes any comment on the contribution of the TCRa-chain, the current analysis does allow us to state definitively that distinct CTL populations are responsible for conferring avidity and polyfunctional phenotypes in the D b PA 224 -specific population. One might have anticipated differences between the previous analysis of avidity based on the sensitivity of TCR-pMHCI binding (which takes into account both the on-and off-rates of binding) and the current analysis that is based on the TCR-pMHCI dissociation rate, a measure that has been shown previously to correlate with different levels of polyfunctionality for D b NP 366 -and D b PA 224 -specific populations (14,19). The fact that these two strategies for subsetting high-avidity cells yielded a similar difference (selectively in the D b PA 224 -specific subset), and enrichment of the same TCRb clonotype (SLGGYEQ) in some mice, suggests that the contribution of TCRb clonotype to avidity that was detected in the earlier study (21) was dictated primarily by the effects on dissociation rate and not the on-rate of binding.…”

“…Further evidence that cytokine profiles are determined independently of TCR avidity comes from our earlier observation that the threshold of stimulation required for the production of IFN-g, TNF-a, and IL-2 in influenza epitopespecific CTL populations is equivalent. That is, polyfunctional epitope-specific CTLs were found at comparable prevalence when cells were stimulated with optimal or suboptimal peptide concentrations and in CD8-dependent and -independent responses (19). Although some apparent differences in clonotype usage were observed in the current study between the D b NP 366 -specific IFN-g versus IL-2 groups for particular mice [i.e., notably mice 3 and 5 (Supplemental Table III)], such differences were not generally characteristic of these groups, and the total analysis of all nine mice in this group did not support the contention that TCRb clonotype is able to confer polyfunctionality at the global level.…”

“…The response characteristics after both primary and secondary influenza infection have been extensively characterized for a range of epitope-specific CD8 + T cell populations (14,(18)(19)(20). In particular, cytokine production, as determined by intracellular cytokine staining, is hierarchical in character, with most of the epitope-specific CTLs producing IFN-g, whereas some are IFN PA 224 -specific populations has now been extended by analyzing avidity based on the TCR-pMHCI dissociation rate, one of only two avidity measures that correlates with polyfunctionality in these populations (14,19). Critically, we also analyzed TCRb usage for the D b NP 366 -and D b PA 224 -specific CD8 + IL-2 + sets and compared this with TCRb usage in the total epitope-specific IFN-g + repertoires within the same mice.…”

“…The tetramer dissociation assay provides a relative measure of the duration of the TCR-pMHCI interaction for polyclonal epitopespecific T cell populations (14,19,27) PA 224 -specific sets, the population isolated at 60 min represented between 13 and 20% of the maximum staining observed at time 0 (Fig. 1A, 1C).…”