Morphological and enzyme-histochemical changes of the mouse thymus after hydrocortisone.

This study was designed to determine the effect of hydrocortisone on morphology and enzyme-histochemistry of the thymus, on the peripheral blood cell picture, and on skin graft survival time in mice. In addition to the prolongation of survival of skin grafts, to a dose-dependent lymphopenia, and to an increase in the number of circulating neutrophil granulocytes, we found morphologically enlarged epithelial reticular cells with large cytoplasmic vacuoles, which often formed cyst-like structures. Because of their broad enzyme activity it may well be that these epithelial cell derived cysts regulate by means of humoral factor(s) the repopulation of the thymic cortex. In addition semithin sections clearly showed that the polymorphonuclear-like cells in the thymic cortex are altered lymphocytes with fragmented nuclei.