Anti-endotoxic Activity of Murine Monoclonal Antibody (E5) Assessed by Inhibition of Priming of Human Phagocytes by Endotoxin

Abstract

The in vitro activity of a murine monoclonal antibody (E5) reactive with endotoxin was examined in human whole blood by measuring the luminol-chemiluminescence (CL) activity in response to phorbol myristate acetate (PMA) as an index of the priming effect of lipopolysaccharide (LPS) on the release of reactive oxygen species. Whole blood samples obtained from healthy adults showed a significantly enhanced CL response to PMA after incubation with LPS (100 ng/ml, Escherichia coli O111: B4) for 10 min at 37 & deg;C, as compared with untreated blood samples, though no CL response was induced by LPS itself. This priming effect of LPS varied from person to person. Similarly, various degrees of the priming effect were observed with other LPS preparations derived from E. coli O55: B5, Klebsiella pneumoniae, Serratia marcescens and Salmonella typhimurium. However, the priming effects of these LPS or a synthetic lipid A (LA-15-PP) of E. coli were significantly prevented to various degrees when such endotoxins were treated with E5 for 30 min at 37 & deg;C prior to being added to blood samples. The inhibitory effect E5 was dosedependent and was most potent against the LPS of E. coli O111: B4.
These results indicate that E5 suppresses the priming effect of LPS on oxygen radical release from human whole blood, and therefore suggest that E5 may be a useful drug for supportive therapy in patients with gram-negative septicemia or endotoxemia, especially in a case involving serious neutrophil-mediated organ injury caused by excessive release of oxygen free radicals.