Characterization of dynamic actin associations with T-cell receptor microclusters in primary T cells.

T cell triggering through T-cell antigen receptors (TCRs) results in spatial assembly of the receptors on multiple length scales. This assembly is mediated by the T cell actin cytoskeleton, which reorganizes in response to TCR phosphorylation and then induces the coalescence of TCRs into microclusters, followed by their unification into a micrometer-scale structure. The exact outcomes of the association of TCRs with a dynamic and fluctuating actin network across these length scales are not well characterized, but it is clear that weak and transient interactions at the single-molecule level sum to yield significant receptor rearrangements at the plasma membrane. We used the hybrid live cell-nanopatterned supported lipid bilayer system to quantitatively probe the actin-TCR interaction in primary T cells. A specialized tracking algorithm revealed that actin slows as it passes over TCR clusters in a direction-dependent manner with respect to the resistance against TCR motion. We also observed transient actin enrichments at sites corresponding to putative TCR clusters that far exceeded pure stochastic fluctuations and described an image time-autocorrelation analysis method to quantify these accumulations.