Strong and Durable TCR Clustering at the T/Dendritic Cell Immune Synapse Is Not Required for NFAT Activation and IFN-γ Production in Human CD4+ T Cells12

The exact function of TCR clustering and organized macromolecular patterns at the immune synapse between APCs and T lymphocytes is unclear. Using human immature or mature dendritic cells (DCs) and autologous CD4+ effector T cells, we demonstrate that, within a given conjugate, mature DCs induce strong and long-lasting TCR clustering and protein kinase C-θ translocation in a superantigen dose-dependent manner. Moreover, mature DCs promote CD43 exclusion in a dose-independent manner. In contrast, immature DCs are less potent at inducing these molecular rearrangements. Using these models to correlate T cell functions with the frequency, the intensity, and the duration of TCR clustering, we show, in Jurkat T cells, that weak and transient TCR clustering is sufficient to promote TCR down-modulation, protein kinase C-θ translocation at the synapse, and substantial NFAT transcriptional activation. Moreover, we show, in CD4+ T cell blasts, that strong TCR clustering is required for neither TCR down-modulation nor optimal IFN-γ production. Together, our results demonstrate that some CD4+ functional responses, such as cytokine production, are independent of central supramolecular activation cluster formation.