Immunoreactivity and bioactivity of lipopolysaccharide-binding protein in normal and heat-inactivated sera

The lipopolysaccharide (LPS)-potentiating effect of serum is due to LPS-binding protein (LBP), which facilitates the binding of LPS to CD14 receptors. We observed a remarkable heat sensitivity of recombinant LBP and various sera with respect to both immunoreactivity (measured by enzyme-linked immunosorbent assay) and bioactivity (potentiation of LPS induction of tumor necrosis factor in monocytes). Human sera were more active and more heat sensitive than fetal bovine sera. The commonly practiced heat inactivation of human serum (56 degrees C, 30 min) resulted in a 70% loss of bioactivity, which caused an apparent decrease in the potency of LPS.