Repeated in vivo hydrocortisone treatment promotes a dual modulation of cytokeratin expression by mouse thymic epithelial cells.

Previous studies showed that a single dose of hydrocortisone in mice was able to transiently upregulate the expression of cytokeratins (CKs) 3 and 10 by medullary epithelial cells of the mouse thymus. Herein we studied these cells (specifically recognized by immunocytochemistry with the anti-CK monoclonal antibody KL1) following a series of repeated injections of the glucocorticoid hormone. A progressive dual (up and down) modulation of KL1+ medullary epithelial cells was observed with a late appearance of KL1 immunoreactivity in the thymic cortex. The data indicate that a single versus repeated exposure to high doses of glucocorticoid hormone may trigger different circuits regulating intrathymic CK expression. Lastly, the model described herein may be regarded as promising in studies concerning the effect of repeated stress conditions upon the thymus.