Actin and agonist MHC-peptide complex-dependent T cell receptor microclusters as scaffolds for signaling

T cell receptor (TCR) microclusters form within seconds of T cell contact with supported planar bilayers containing intercellular adhesion molecule-1 and agonist major histocompatibility complex (MHC) - peptide complexes, and elevation of cytoplasmic Ca2+ is observed within seconds of the first detectable microclusters. At 0 - 30 s after contact, TCR microclusters are colocalized with activated forms of Lck, ZAP-70, and the linker for activation of T cells. By 2 min, activated kinases are reduced in the older central microclusters, but are abundant in younger peripheral microclusters. By 5 min, TCR in the central supramolecular activation cluster have reduced activated kinases, whereas faint peripheral TCR microclusters efficiently generated activated Lck and ZAP-70. TCR microcluster formation is resistant to inhibition by Src family kinase inhibitor PP2, but is abrogated by actin polymerization inhibitor latrunculin A. We propose that Src kinase - independent formation of TCR microclusters in response to agonist MHC - peptide provides an actindependent scaffold for signal amplification.