Laminin-211 controls thymocyte--thymic epithelial cell interactions.

Thymocyte differentiation occurs within the thymic microenvironment, consisting of distinct cell types and extracellular matrix (ECM) elements. One of these ECM proteins is laminin. Previous experiments showed that laminin mediates interactions between thymocytes and thymic epithelial cells (TEC) in mice. Since, laminin comprises a family of related isoforms, we searched for laminin isoform expression in the human thymus. We found constitutive gene expression of various laminin chains in TEC preparations, comprising laminin-111 and laminin-211 isoforms. Immunocytochemistry revealed a selective laminin-211 distribution in the thymic lobules. In vitro functional assays revealed that laminin-211 enhances TEC/thymocyte adhesion and thymocyte release from thymic nurse cells, as well as the reconstitution of these complexes. Conversely, these interactions are blocked by monoclonal antibodies specific for laminin-211 and the laminin receptor VLA-6. Our results reinforce the notion that distinct laminin isoforms in the human thymus are relevant for lymphoepithelial interactions.