TFPI interferes with LBP-LPS interaction by binding to LPS. (A) TFPI blocks LBP-mediated transfer of LPS to rHDL. LBP-mediated BODIPY-LPS transfer to rHDL was measured as described in the Materials and Methods. BODIPY-LPS (0.5 μg/mL), rLBP (5 μg/mL), rHDL (20 μg/mL), and the indicated amounts of rTFPI were mixed and incubated for 2.5 hours in room temperature. At this time point, the transfer of BODIPY-LPS to rHDL was completed. The transfer was expressed as RF(%), which represents the ratio of fluorescence measured to the total amount of fluorescence in the sample. Samples were in triplicate, and average standard deviation are shown. The triangle represents a control sample in which BODIPY-LPS was incubated with LBP alone without rHDL. Experiments were repeated twice with essentially identical results. Data are plotted on logarithmic X scale. (B) TFPI interferes with binding of LBP to LPS-coated surface. Binding of rLBP to LPS-coated terasaki plates in the presence of rTFPI was measured by enzyme-linked immunosorbent assay (ELISA) methodology as described in the Materials and Methods. Plates were either coated with LPS (•) or buffer (▴) and rLBP (0.1 μg/mL) was added in the presence of the indicated amounts of rTFPI. (C) TFPI binds to LPS-coated surfaces. Binding of rTFPI to LPS-coated plates was measured by the ELISA methodology as described in the Materials and Methods. (○) Total binding; (▵) nonspecific binding on buffer-coated surface; (▪) specific binding to LPS (total binding subtracted with nonspecific binding).