Ultrastructural alterations of the cortical epithelial cells of the rat thymus after cyclophosphamide treatment.

A single dose of cyclophosphamide (CY) was administered to Sprague-Dawley rats to investigate the effects of CY on thymic cortical epithelial cells (TCE) at the ultrastructural level. The most striking finding among the alterations in the TCE after CY treatment was a cytoplasmic vacuolization with an increased amount of granular and membranous content. The granular content appeared not only as dense bodies but also as loosely aggregated forms or finely dispersed granules. The membranous structures appeared in various forms including vesicular, tubular, vacuolar and irregular membranous structures and myelin figures. Some of the membranous structures contained granular material. Several vacuoles were closely associated with the endoplasmic reticulum (ER). The morphological alterations of the ER were also remarkable. The Golgi apparatus, mitochondria and vesicles increased in number. The cytoplasm became densely granulated due to an increased number of ribosomes and an increased amount of granular material. The tonofilaments lost their original array and increased in amount. The cell surface exhibited many cytoplasmic processes like microvilli. It seems that the above features result not only from some damage by CY, but also signs of a hyperfunctional state of the TCE, probably due to their important functions in repopulation and maturation of the cortical thymocytes during recovery after CY-induced acute thymic involution, including the secretion of some humoral factors.