Quantitative light and electron microscopic changes in thymic reticular epithelial cells during Moloney-virus-induced lymphoma development

This report describes two types of reticular epithelial cell in the thymic cortex of the BALB/c mouse, an immature and a mature form. During early stages of lymphoma development, i.e., 2-6 weeks postinfection (p.i.) with Moloney leukemia virus (M-MuLV), activation of the epithelial cells is observed. Although the percentage of these cells in the total cell population of the thymic cortex remains constant during that time, the number of mature epithelial cells is significantly increased in infected animals. Subsequently, about 6 weeks p.i., the number of immature epithelial cells starts to increase, whereas the number of mature reticular epithelial cells declines and the appearance of the mature epithelial cells changes drastically. The results of light and electron microscopic studies indicate degeneration of the mature reticular epithelial cells at the onset of lymphoma development at a time when the first deficiencies in the immunologic competence of the reticular epithelial cells are apparent.