Abstract
Summary The effect of serum on endotoxin from S. enteritidis was studied by incubating I125-labeled lipopolysaccharide with antiserum and precipitating the antibody-bound antigen with an equal volume of saturated ammonium sulfate at various time intervals. Degradation was determined by the decrease in radioactivity of the antibody-bound antigen as low molecular weight labeled fragments of lipid were removed from the endotoxin molecular complex. A purified endotoxin preparation, low in lipid, was degraded by a factor present in normal, tolerant or immune rabbit serum and normal human serum. On the other hand, a semi-purified preparation richer in lipid was not degraded by serum or plasma, but removal of its lipid by nonhydrolytic procedures yielded a product that was degraded. Degradation was inhibited by mercuric chloride, protamine sulfate and Neomycin sulfate. Pancreatic lipase was more effective than serum, and degraded the endotoxin preparation of high lipid content. A euglobulin fraction obtained from guinea pig plasma collected 15 min after injection of heparin was considerably more active than whole plasma or the euglobulin fraction of plasma from nonheparinized animals. The supernatant fluid remaining after euglobulin precipitation contains an inhibitor of degradation by both plasma and pancreatic lipase. It appears that lipolysis by serum lipase is an early step in the process of degradation and detoxification of endotoxin.
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