Endotoxin Inactivating Activity of Rat Serum

Abstract

The ability of rat serum to inactivate endotoxin (LPS) was assessed with the aid of the limulus amebocyte lysate assay. Following the addition of various amounts of endotoxin to normal serum the mixture was incubated for 1 hr at 37°C and the residual endotoxin activity determined. One milliliter of rat serum inactivated between 5 and 10 pg Escherichia coli LPS per hour. Heating serum for 45 min at 56°C resulted in loss of 80-90% of the LPS inhibitor (LPSI) activity. Serum from cobra venom factor (CVF)-treated rats inactivated between 0.5 and 2.5 pg LPS/ml serum. Serum from tolerant rats, even after heating for 45 min at 56"C, inactivates between 10 and 15 pg LPS/ml serum/hr; decomplemented tolerant rat serum neutralizes between 5 and 10 pg LPS/ml serum/hr. Clearly, the tolerant rat has large quantities of LPSI activity, which does not appear to be complement. The inhibitor found in tolerant rat serum is not species specific since it inactivates Salmonella minnesota and Salmonella typhimurium endotoxins to the same degree and in the same amount as E. coli endotoxin, the agent used to induce tolerance. Both heating serum (56°C) and lead acetate reduce LPSI activity. o

Endotoxin Neutralization as a Biomonitor for Inflammatory Bowel Disease

“…This report attempts to quantitate and characterize endotoxin neutralization to monitor immune system activation in response to Gram-negative bacterial exposure and then test that system in patients with IBD. Consistent with previous reports, we found that a purified endotoxin stock was almost completely (>99%) neutralized after incubation in plasma for 10 minutes [22]. Heating the plasma prior to endotoxin addition decreased the level of neutralization significantly, suggesting that heat-labile factors, such as IgM and enzymatic activity, were responsible for a portion, but not all of the neutralization [20].…”

“…It has been well established that there are components in mammalian blood that neutralize endotoxin [20–22]. This report attempts to quantitate and characterize endotoxin neutralization to monitor immune system activation in response to Gram-negative bacterial exposure and then test that system in patients with IBD.…”