Ultrastructural changes in murine peritoneal cells following cyclophosphamide administration.

Peritoneal cells were studied at intervals of between 6 h and 30 days following a single intravenous injection of a sublethal dose of cyclophosphamide. With the electron microscope, evidence of cell damage and death could be seen at 6 h, and by 12 h large numbers of dead cells were noted, either lying free or within the cytoplasm of macrophages. Most of the damaged cells were lymphocytes but degenerating blast cells, eosinophils, neutrophils and mast cells were also identified. Nuclei were seen in which margination of chromatin had occurred but nuclei of uniform density were also prominent and showed irregular shape and lobulation. Macrophages exhibited all stages of phagocytosis and digestion and a few phagocytes of atypical appearance were noted. By 24 h most of the dead cells lay within the cytoplasm of macrophages which showed many phagocytic inclusions as well as lipid droplets. By 6 days, the peritoneal cells had regained normal appearances although the proportion of lymphoid cells was still reduced. By the 18th day, all features were indistinguishable from normal. The changes observed showed a general similarity to those noted previously in the lymphoreticular cells of the Peyer's patch; they provide no evidence that the environment of the peritoneal cavity protects cells against the action of cyclophosphamide.