Studies with radioactive endotoxin. III. Localization of 3H-labelled endotoxin in the formed elements of the blood and detection of endotoxin in calf blood with the Limulus amebocyte lysate.

(3)H-labelled Pseudomonas endotoxin was incubated in vitro with blood from nontolerant and endotoxin tolerant calves. Formed elements were separated from serial samples of the incubated mixtures. The labelled endotoxin became associated with neutrophils, monocytes, lymphocytes, platelets and erythrocytes. Association of (3)H-endotoxin with formed elements of the blood occurred during the first five minutes of incubation and did not significantly change over the course of a three hour incubation period. Tolerance did not result in increased uptake of (3)H-endotoxin by formed elements of the blood. Tolerance of calves to endotoxin is apparently not due to increased uptake of endotoxin by formed elements of the blood. The Limulus amebocyte lysate assay was unreliable for the detection of endotoxin which was present in calf blood in vitro and requires further modification.