Dose dependence of endotoxin-induced activation of the plasma contact system: an in vitro study

The dose and time dependence of endotoxin-induced activation of the plasma contact system have been studied. Citrated pool plasma was incubated at 37 degrees C with endotoxin doses of 2.10(5), 2.10(6), 2.10(7), and 2.10(9) ng/l (lipopolysaccharide B, E. coli 026: B6, Difco Laboratories, Detroit, MI) for 24 hr. Samples for determination of components of the contact system were obtained prior to incubation and at 1, 2, 4, 6, 12, and 24 hr. Plasma kallikrein (KK) activity markedly increased at 12 hr in test plasma containing the highest dose of endotoxin (2.10(9) ng/l). Coincident with the elevated KK activity, reductions of both plasma prekallikrein (PKK) and functional kallikrein inhibition (KKI) were seen as assayed by chromogenic peptide substrate analyses. Also, functionally determined alpha 2-macroglobulin (alpha 2-M) and C1 inhibitor (C1INH) values were decreased, confirming the reduction of KKI values. Changes of Hageman factor (FXII), PKK, and high molecular weight kininogen (HMWK) values were also found at the same time point when assayed by immunochemical techniques. The same pattern of changes was seen in test plasma containing 2.10(7) and 2.10(6) ng/l of endotoxin. These changes, however, were less pronounced and not seen until 24 hr after beginning incubation. In control plasma and in plasma containing the lowest dose of endotoxin (2.10(5) ng/l), no changes were seen in any factors of the contact system. Our study shows that in vitro endotoxin-induced activation of the contact system is a slow process that is both time and dose dependent.