Figure 4.

Retrograde trafficking in immune cells. T-cell receptor (TCR) activation occurs in the presence of antigen presenting cells (APC). During this event, T lymphocytes build specialized membrane domains, termed immunological synapses (IS) to which the linker for activation of T-cell (LAT) localizes in a polarized and dynamic manner to organize the signalosome. Here again, the Golgi apparatus is localized in a polarized manner such that it directly faces the IS. (a) LAT efficiently undergoes Rab6, retromer, and Synt16-dependent retrograde trafficking to the Golgi compartment for subsequent polarized secretion to the IS, a trafficking loop that is required for efficient T cell activation. (b) LAT and other T-cell components such as TCR as well as APC cargoes such as CD166 have been reported to be internalized in a clathrin-independent manner. Whether similar to LAT the other cargoes also undergo retrograde transport for their dynamic localization to the IS remains to be studied directly.