Capture of LPS by the human fibrin clot1.

1LPS was added to a suspension of platelet-depleted plasma at the concentrations indicated in column 1, then the suspension was induced to clot by the addition of LPS-free recombinant thrombin. This is plasma from the same sample of blood used for Table 3, after removal of the platelets by centrifugation with a microcentrifuge at top speed. After a 1 h incubation at 37°C, the fibrin clot was removed and the serum was diluted in LPS-free water as indicated in column 2, heated for 10 min at 70°C, and assayed by the LAL test (column 3), as described in Materials and Methods. The sensitivity of the assay was 0.1 ng/mL LPS, but due to the dilution of the experimental samples, the maximum concentration of free LPS remaining in solution in the serum was correspondingly elevated, as indicated in column 4. Subtraction of maximum free concentration of LPS from the initial concentration yields the minimum amount of LPS captured by 1 mL of platelet-rich plasma (column 5). Selected data points from this individual trial were replicated in 7 additional trials.