Effects of Bacterial Endotoxin on the Occurrence of Spleen Colonies in Irradiated Mice

Abstract

It is generally agreed that survival in the midlethal radiation dose range depends principally on hemopoietic recovery. Administration of endotoxin as a single injection either before or shortly after irradiation in the mouse hastens recovery of granulocytes, erythrocytes, platelets, and lymphocytes (1, 2), increases resistance to infection (3), and reduces mortality (4). In contrast, multiple injections given before irradiation cause no advance in leukocyte recovery or increase in survival (4, 5), even though such injections in nonirradiated mice cause greater increases in spleen weight and resistance to bacterial challenge than a single injection. Till and McCulloch have observed that nodules seen in the spleen 10 days after irradiation are erythroid, granulocytic, megakaryocytic, or mixed (6) and that their number is related to radiation dose and survival (7, 8). The present experiments show that a single injection of endotoxin increases splenic nodules as well as granulocyte count and survival. In contrast, the multiple injections increase the number of splenic nodules (though to a lesser extent) without promoting marrow recovery or survival.