Laminin chains in the basement membranes of human thymus

The laminin a2 chain has been suggested to be the only laminin a chain expressed in mouse and human thymus. Here, the authors use monoclonal antibodies to study the expression of laminin chains in samples of fetal and 6-year-old human thymus. The subepithelial basement membrane of the capsule of fetal 16- to 18-week thymus presented a bright immunoreactivity for laminin a1, a3, B1, B3 and g1 chains but not for a2 chain, suggesting the expression of laminin-111 and -332. Most cortical and medullary epithelial cells, including Hassall’s corpuscles, however, lacked laminin immunoreactivity. In thymic specimens from 6-year-old children, immunoreactivity for the laminin a1, a3, B1, B3 and g1 chains were invariably found in the subepithelial basement membrane of the capsule and that for laminin a2 chain was now also distinct but more heterogeneous. The present results show that the thymic subepithelial basement membrane of the capsule presents properties that are commonly seen in stratified and combined epithelia, and are compatible with suggestions of the antigenic similarity of thymic epithelial cells and keratinocytes.