Abstract
The use of monoclonal antibodies (mAbs) directed to lipid A for the therapy of gram-negative sepsis is controversial. In an attempt to understand their biologic basis of action, we used a fluid-phase radioimmunoassay to measure binding between bacterial lipopolysaccharide (LPS) and two IgM mAbs directed to lipid A that are being evaluated for the treatment of gram-negative bacterial sepsis. Both antibodies bound 3H-LPS prepared from multiple strains of gram-negative bacteria when large excesses of antibody were used, although binding was modest and only slightly greater than control preparations. We also studied the ability of each anti-lipid A antibody to neutralize some of the biological effects of LPS in vitro. Despite large molar excesses, neither antibody neutralized LPS as assessed by the limulus lysate test, by a mitogenic assay for murine splenocytes, or by the production of cytokines interleukin (IL)-1, IL-6, or tumor necrosis factor from human monocytes in culture medium or in whole blood. Our experiments do not support the hypothesis that either of these anti-lipid A mAbs function by neutralizing the toxic effects of LPS.
Highlights
From the Departments of *Medicine and *Ghildrens Service, Infectious Disease Units, Massachusetts General Hospital, Charlestown, Massachusetts 02129; $Shriners Burns Institat~
In an attempt to understand their biologic basis of action, we used a fluidphase radioimmunoassayto measure binding between bacterial lipopolysaccharide (LPS) and two IgM monodonal antibodies (mAbs) directed to lipid A that are being evaluated for the treatment of gram-negativebacterial sepsis
Wells contained indicated amounts of LPS and antibody or 1/~g polymyxin 13. These studies demonstrate that anti-lipid A mAbs HA1A and E5 bind only weakly to LPS from multiple clinically relevant smooth gram-negative bacteria, and are unable to neutralize the biological effectsof LPS in severalin vitro assays
Summary
From the Departments of *Medicine and *Ghildrens Service, Infectious Disease Units, Massachusetts General Hospital, Charlestown, Massachusetts 02129; $Shriners Burns Institat~. In an attempt to understand their biologic basis of action, we used a fluidphase radioimmunoassayto measure binding between bacterial lipopolysaccharide (LPS) and two IgM mAbs directed to lipid A that are being evaluated for the treatment of gram-negativebacterial sepsis Both antibodies bound 3H-LPS prepared from multiple strains of gram-negative bacteria when large excessesof antibody were used, binding was modest and only slightly greater than control preparations. We evaluated the ability of each anti-lipid A antibody to neutralize the effects of LPS in several in vitro assays of endotoxin bioactivity We found that both HA-1A and E5 bound slightly to LPS from multiple smooth strains of gramnegative bacteria when large excesses of antibody were used.
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