FIG. 5.

Model of LBP-LPS interaction that depends on LBP concentrations in cellular activation and clearance of different LPS chemotypes. Low concentrations of LBP enhance cellular activation by all major chemotypes of LPS brought about by an interaction with the cellular LPS receptor consisting of TLR-4, MD-2, and CD14 (pathway 1). High concentrations of LBP, such as those present in normal and acute-phase human sera, inhibit LPS-induced cell stimulation by different pathways. While LBP induces a silent uptake of the types of R-type LPS used here in a largely CD14-independent fashion (pathway 2), S-type LPS is internalized without NF-κB activation in a strictly CD14-dependent manner (pathway 3). Furthermore, in the presence of serum or lipoproteins, S-type but not R-type LPS is preferentially transferred into lipoprotein particles by hd-LBP (pathway 4).