Pre-clustered TCR complexes.

The T-cell antigen receptor (TCR) is a multisubunit transmembrane complex that mediates the antigen-specific activation of T cells. Using a variety of techniques, several research groups have shown that TCRs are at least partially pre-clustered before antigen binding. These new findings are contradictory to the "classical" view, according to which TCRs are randomly distributed on the cell surface and only associate upon antigen binding. In this review we try to answer the following questions: What are the experimental evidences for the existence of pre-clustered TCRs? How can the TCR pre-clusters be activated upon antigen binding? Which functional consequences for T-cell activation arise from the pre-clustering of TCRs.