Strong expression of L26 antigen in epithelial cells of human neonatal thymus. An immunohistochemical study using light and electron microscopy.

L26 antigens (33- and 30-kDa proteins) are known to be present in human B lymphocytes. We have found that L26 antigens were strictly confined to the thymic medulla. However, the L26 antigens were not as abundant as those in human tonsils. At the ultrastructural level, L26 antigen-positive cells corresponded to thymic epithelial cells with thick bundle-like cytoplasmic filaments. These features may be useful for the identification of thymic epithelial cells both in vitro and in vivo.