TCR microclusters are defined structures that contain a variety of signaling molecules and are involved in the activation of T cells. In the Journal of Immunology, Varma and colleagues find that TCR microclusters preexist even in truly naive cells with transgenic TCR expression that have never encountered agonist ligand. These preexisting microclusters contain a constant number of TCRs and key T cell signaling adaptors (such as Grb2 and Lat) and, furthermore, exclude the receptor phosphatase CD45. Thus, the microclusters have many of the structural and compositional characteristics required for the effective activation of T cells. It remains unclear how these ligand-indpendent microclusters are initially formed, but their preexistence may help facilitate the rapid signaling observed in T cells after they encounter high-affinity agonist peptide.

J. Immunol. 193, 56–67 (2014)