Corticosteroid treatment and X-ray irradiation in adult rats induce the reexpression of fetal markers in cortical thymic epithelial cells.

The phenotype of cortical thymic epithelial cells (TEC) following hydrocortisone-treatment and sublethal X-ray irradiation in adult rats was studied by immunohistochemistry. It was found that during thymic regeneration (2-16 days) a TEC subset, predominantly in the outer cortex, transiently expressed cytokeratin (CK) 19 and an antigen defined by PT13D11 monoclonal antibody (mAb). These markers are characteristic for fetal, but not adult cortical TEC. To examine whether regenerating thymocytes may influence the phenotype of cortical TEC we cultivated a rat cortical TEC line (R-TNC 1.1) with thymocytes isolated from the thymuses at day 7 after hydrocortisone treatment. The R-TNC 1.1 TEC line, although established from adult rat thymus, constitutively expresses PT13D11, but not CK19. The appearance of CK19 in the R-TNC 1.1 cells was not inducible neither by coculture of this line with thymocytes, nor by the influence of IL-1, IL-2, IL-6, TNF-alfa and IFN-gamma. These results demonstrated the phenotypic plasticity of cortical TEC in adult rats.