Thy-1 signaling in the context of costimulation provided by dendritic cells provides signal 1 for T cell proliferation and cytotoxic effector molecule expression, but fails to trigger delivery of the lethal hit.

Cross-linking of the GPI-anchored protein Thy-1 results in T cell proliferation and IL-2 synthesis. However, the exact function of Thy-1 in the process of T cell activation remains unknown, as does the effect of costimulation on Thy-1-driven T cell responses. In this study, we have investigated the ability of Thy-1 to substitute for traditional signal 1 in the context of costimulation provided by dendritic cells.