Endotoxin concentration by Limulus assay correlates with biological activity in mice and human peripheral blood mononuclear cells

Endotoxin is thought to play a major role in septic shock and multiple systemic organ failure (MOF). However, endotoxin is not always detected in the plasma during Gram-negative sepsis by current Limuluslysate assays. Additionally, it is unknown to what extent the biological activity of endotoxin is truly reflected in endotoxemia. This paper assesses quantitatively a comparison of three types of Limulusassays for the detection of the biological activity of endotoxin in plasma. Mouse lethal activity and TNF production were used for assessment of the biological activity of endotoxin both before and after potential modification of LPS activity by plasma constituents. We have concluded that the dilution and heating method coupled with a toxinometer provides the most accurate correlation with other biological activities of endotoxin in plasma. The fact that the biological activity of endotoxin decreased to 17% of initial dose after incubation at 37ºC for 90 min in normal plasma suggests further a temporal dependence of time in plasma upon the manifestation of biological activities normally attributable to this biologically active microbial constituent found in the plasma of septic patients.