Endotoxin-binding and -neutralizing properties of recombinant bactericidal/permeability-increasing protein and monoclonal antibodies HA-1A and E5.

OBJECTIVE

To compare the endotoxin-binding and -neutralizing properties of bactericidal/permeability-increasing protein, the human monoclonal antiendotoxin antibody HA-1A, and the murine antiendotoxin antibody E5.

DESIGN

Prospective, randomized, placebo-controlled laboratory study.

SETTING

Biotechnology company research laboratory.

SUBJECTS

Female CD-1 mice.

INTERVENTIONS

Recombinant bactericidal/permeability-increasing protein, HA-1A, a human immunoglobulin M monoclonal antibody raised against Escherichia coli J5 (Rc) endotoxin, and E5, a murine immunoglobulin M monoclonal antibody raised against E. coli J5 endotoxin, were compared in the following assays: a) binding to rough lipopolysaccharide immobilized onto microtiter plates; b) inhibition of lipopolysaccharide activity in the limulus amebocyte lysate assay; c) inhibition of lipopolysaccharide-induced cytokine release in whole blood; and d) protection against lethal endotoxin challenge in CD-1 mice.

MEASUREMENTS AND MAIN RESULTS

The binding affinity of bactericidal/permeability-increasing protein for immobilized lipopolysaccharide is apparently greater than the binding affinity of HA-1A or E5. Bactericidal/permeability-increasing protein neutralized lipopolysaccharide activity in the chromogenic limulus amebocyte lysate assay, while neither monoclonal antibody inhibited lipopolysaccharide activity. Similarly, bactericidal/permeability-increasing protein reduced lipopolysaccharide-mediated tumor necrosis factor production in human whole blood in vitro, whereas monoclonal antibodies had slight (HA-1A) or no (E5) effect on lipopolysaccharide activity in this system. Administration of bactericidal/permeability-increasing protein gave > 90% protection against an LD60 dose of endotoxin in CD-1 mice, while treatment with HA-1A or E5 did not improve survival rate.

CONCLUSIONS

Neither monoclonal antibody was as effective as bactericidal/permeability-increasing protein at binding or neutralizing endotoxin in vitro or in vivo. The potent endotoxin-binding and -neutralizing properties of bactericidal/permeability-increasing protein indicate that it might be useful in the treatment of endotoxin-related disorders in humans.