Endotoxin-neutralizing capacity of serum from cardiac surgical patients

Objective: To determine if endotoxin core antibody (EndoCAb) from the serum of cardiac surgical patients neutralizes endotoxin in an ex vivo biologic assay. Design: Prospective blinded cohort study. Setting: Academic medical center. Participants: Patients (n = 203) undergoing cardiac surgery. Interventions: Sera were obtained from patients preoperatively. Measurements and Main Results: EndoCAb levels were determined by enzyme-linked immunosorbent assay. Sera were incubated for 15 minutes at 37°C with varying concentrations of endotoxin from a clinically relevant bacterium (Escherichia coliserotype O18), then tested for the presence of endotoxin activity using the validated Limulus amebocyte lysate assay. Median (interquartile range) IgM and IgG EndoCAb levels were 118 median units (range, 31 to 259 median units) and 208 median units (range, 108 to 401 medium units). Increasing levels of IgM EndoCAb were associated with increased neutralization of endotoxin (p < 0.0001). Increasing levels of IgG EndoCAb were associated with increased neutralization of endotoxin (p < 0.0001). An additive effect of IgM and IgG EndoCAb levels on endotoxin neutralization was observed without evidence of synergistic or plateau effects. EndoCAb levels did not completely predict serum neutralization capacity. Conclusion: Anti-EndoCAbs of both classes (IgM and IgG) were able to neutralize lipopolysaccharide from a clinically relevant bacterium in an ex vivo model. Neither Igm nor IgG appeared to be more capable of neutralization in this model. These antibodies did not completely predict neutralization capacity; other endogenous factors in human serum must be capable of lipopolysaccharide neutralization.