Evidence for the expression of Thy-l-analogous structures on human thymic epithelial cells.

Cultured human thymic tissue was examined electron microscopically and analysed for the expression of the Thy-l-analogous antigen. It was found that almost all cultured cells were of epithelial appearance, exhibiting both tonofibrils and well-developed demosomes. Absorption of an anti-human brain serum highly purified for antibodies directed against the non-species-specific determinant of the Thy-l-analogous antigen with these cultured cells revealed its presence on thymic epithelial cells. Using the indirect peroxidase-labelled antibody technique, this molecule could be localized on the non-attached cell surface of human thymic epithelial cells with the preference of their cell processes. The biological significance of the expression of this antigen on the thymic epithelial cells of various species for cellular interaction within the thymus is discussed.