Mst1 regulates integrin-dependent thymocyte trafficking and antigen recognition in the thymus

Thymocyte trafficking has an important role in thymic selection. Here we show that the Hippo homologue Mst1 is required for thymocyte migration and antigen recognition by LFA-1 and ICAM-1 within the medulla. Using two-photon imaging of thymic tissues, we found that highly motile mature thymocytes arrest and are activated in the vicinity of rare populations of Aire+ ICAM-1hi medullary thymic epithelia in a negatively selecting environment. Notably, Mst1 deficiency or blocking the cell adhesion molecules LFA-1 and ICAM-1 results in inefficient migration and antigen recognition of CD4+ thymocytes within the medulla. Consistent with these defects, thymocyte selection is impaired in Mst1−/− mice, which display T cell-dependent inflammatory infiltrates in multiple organs and develop autoantibodies. Our results suggest that Mst1 has a key role in regulating thymocyte self-antigen recognition in the medulla. Autoreactive T cells are eliminated as they encounter self-antigens during transit through the thymus. Uedaet al. reveal that mice lacking the Hippo homologue Mst1 develop autoimmunity as a result of impaired integrin-dependent T cell migration through this negatively selective niche.