Immunohistochemical identification of six cytokeratin-defined subsets of the rat thymic epithelial cells.

Rat thymic epithelial cells (TEC) have been studied by a panel of monoclonal antibodies specific for single cytokeratin polypeptides or cytokeratin pairs. Using various combinations of single and double immunostainings 6 TEC subsets (CK types) were identified, each characterized by different cytokeratin expression. Subcapsular/perivascular TEC (TEC-CK type 1) share cytokeratins 7, 8, 19 with a subset of medullary TEC, while cortical TEC were reactive with anti-CK 8 and anti-CK 18 mAbs only (TEC-CK type 2). Additional 4 subsets were identified in the medulla; TEC-CK type 3 (CK 8 + 18 + 19 +), TEC-CK type 4 (CK 8 + 10 + 18 + 19 +), TEC-CK Type 5 (CK 8 + 10 + 10 +) and TEC-CK type 6 positive only with CK 8 of all above cytokeratins. This study extends the concept of TEC heterogeneity and might also be useful to further understanding of TEC origin, development and functions.