Effects of cyclophosphamide on the ultrastructure of Peyer's patches.

An electron microscope study has been made of the Peyer's patches of mice at intervals of between 6 hr and 30 days following a single sublethal injection of cyclophosphamide. Evidence of cellular damage and death was already present in some lymphocytes of the Peyer's patch at 6 hr. An early morphological change was the margination of dense chromatin at the nuclear membrane, with a rather sharp inner border. By 12 hr, large numbers of dead cells were present in the lymphoid tissue, either lying free or within the cytoplasm of macrophages. At 24 hr most of the dead cells and cellular remains were seen to lie within the cytoplasm of macrophages and the lymphoid tissue appeared less cellular than that of the controls. Apparently normal lymphocytes, plasma cells, eosinophils and reticular cells were still present, as well as large binucleate cells which were not seen in the controls. At later intervals, the profiles of the macrophage inclusions appeared smaller. By the 9th day, there was an apparent increase in the cellularity of the lymphoid tissue, and immature forms and cells in mitosis were seen more frequently. By the 18th day, the morphology of the Peyer's patch was indistinguishable from normal.