The Src family kinases Lck and Fyn promote transendothelial migration of T cells

The ability of T cells to cross endothelial barriers and migrate into and within peripheral tissue is crucial for adaptive immunity. Integrins such as LFA-1 play an essential role in this process by acting as adhesion molecules and initiating signaling events that drive the cytoskeletal changes needed for cell migration, however, many of the specific signaling events that promote T cell migration are still unknown. Here, we found that the Src family kinases Lck and Fyn are needed for efficient T cell migration. Primary T cells lacking Lck, Fyn, or both kinases exhibited defects in random migration on ICAM-1 coated surfaces for parameters such as speed and mean squared displacement. Analysis of signaling revealed that Lck was required for PI3K signaling downstream of LFA-1, while Fyn was not. Mechanistically, we found that the absence of Lck disrupted the normal interaction of the PI3K regulatory subunit p85 with tyrosine-phosphorylated binding partners, suggesting that Lck may regulate PI3K activity by controlling p85 protein-protein interactions. Importantly, both Lck and Fyn were required for efficient T cell transmigration across an inflamed endothelial barrier, a critical event for tissue infiltration. Lastly, a small-molecule Lck kinase inhibitor also decreased PI3K signaling and T cell transmigration, indicating the kinase activity of Lck is needed. Together, these data identify a new role for Lck and Fyn in promoting T cell transmigration.