We have developed a single molecule imaging technique that uses quantum dot labeled pMHCs to study CD4+ T cell functional sensitivity. We find that both naive and activated T cells can be triggered by a single pMHC to secrete cytokines with a rate of ~1,000 and ~10,000 molecule/min respectively and that additional pMHCs do not increase secretion, thus these cells display a digital response pattern. We also find that a single pMHC induces the formation of a long-lasting TCR microcluster, consistent with a serial engagement mechanism. These data show that scaling up T cell cytokine responses must involve efficient T cell recruitment rather than increasing individual cell cytokine production.
- Copyright © 2013 by The American Association of Immunologists, Inc.