A Closer look at the dynamics of T Cell Receptor Microclusters

Abstract

T cell activation is initiated when T cell receptor (TCR), a transmembrane protein, recognizes antigen presented by antigen presenting cells (APCs). TCRs form microclusters (MCs) within seconds of antigen recognition and are believed to have an important role in early T cell signaling. During activation, TCR-MCs move towards the center of the immunological synapse (IS) formed between the T cell and the APC. We utilized single molecule tracking to investigate the dynamics of single TCRs between and within microclusters. TCRs are fluorescently labelled using two different fluorescent dyes. The labelling density of one of the dyes is kept significantly higher than the other, which allows to simultaneously track TCR microclusters and single TCR molecules in microclusters. Mean Square Displacement (MSD) analysis is used to quantify their dynamics within activating T cells. Our observations reveal that some microclusters merge and split on their way to the IS center with merging and splitting observed more frequently on the cell periphery. Observations suggest that a single TCR remains associated with its specific microcluster, exhibiting no movement between microclusters unless the microclusters merge. This behavior may be due to the recruitment of other crucial proteins and signaling molecules involved in early T cell signaling, such as LAT, Lck and ZAP-70 among others, to TCR microclusters.