Actin' off: PD-1 suppresses F-actin rearrangement and degranulation at the immunological synapse.

Programmed cell death molecule 1 (PD-1) is a negative regulator of T cell activation; however, the mechanisms by which it acts are unclear. In this issue of Science Signaling , Paillon et al . show that PD-1 inhibits actin cytoskeletal rearrangements and associated effector responses in cytotoxic T cells.