Cytoskeletal polarization and redistribution of cell-surface molecules during T cell antigen recognition

T cell antigen recognition is accompanied by cytoskeletal polarization towa rds the APC and large-scale redistribution of cell surface molecules into ' supramolecular activation clusters' (SMACs), forming an organized contact i nterface termed the 'immunological synapse' (IS). Molecules are arranged in the IS in a micrometer scale bull's eye pattern with a central accumulatio n of TCR/peptide-MHC (the cSMAC) surrounded by a peripheral ring of adhesio n molecules (the pSMAC). We propose that segregation of cell surface molecu les on a much smaller scale initiates TCR triggering; which drives the form ation of the IS by active transport processes. IS formation may function as a checkpoint for-full T cell activation, integrating information on the pr esence and quality of TCR ligands and the nature and activation state of th e APC.