Fate of intravenously injected human tumor cells in the lung of nude mice following whole-body X-irradiation.

X-irradiation administered to nude mice and the ensuing pulmonary metastasis of injected human tumor cells were investigated. When human tumor cells (5 X 10(5)) were injected into the tail vein of male adult nude mice 5 days after 3 Gy whole-body X-irradiation, the incidence of pulmonary metastasis was more frequent in the irradiated mice than in the nonirradiated controls. Platelet aggregation and fibrin deposition around the tumor cells were present in the capillaries of the lung in the irradiated mice while prominent neutrophilic infiltration was noted around the tumor cells in the nonirradiated controls. Fibrinolytic activity of the lung was decreased in the irradiated mice, while serum fibrinogen level was increased after irradiation. Natural killer cell activity was decreased after irradiation. We conclude from this study that increase in serum fibrinogen levels and decrease in fibrinolytic activity of the lung, as a target organ, together with decreased infiltration of neutrophils, may be related to the trapping and lodgement of tumor cells when nude mice are subjected to irradiation.