Surface molecules essential for positive selection are retained but interfered in thymic epithelial cells after monolayer culture

It has been reported that the three-dimensional structure of thymic epithel ial cells (TECs) is responsible for thymic positive selection but that this ability disappears when TECs are cultured in monolayer. These results have supported the hypothesis that certain TEC-specific molecules are extinguis hed during monolayer culture. In this study, using MHC class II-restricted T-cell receptor transgenic mice, we demonstrated that preselected CD4(+)8() (DP) thymocytes were inhibited from developing into CD4(+)8(-) (CD4SP) ce lls in reaggregate thymus organ culture with monolayer-cultured TECs, but t his inhibition was removed when TECs were cultured in monolayer with protei n synthesis inhibitor or when the cultured TECs were treated with fixative. These results seem to be inconsistent with the previous hypothesis and ind icate that monolayer culture allows TECs to retain the surface molecules ne cessary for positive selection but interferes with their function, which mu st be sustained for three dimensional structure. (C) 2001 Academic Press.