Inactivation of endotoxin by a humoral component. III. Role of divalent cation and a dialyzable component

The uniformly high potency of citrated plasma as compared with the limited capacity of serum to inactivate endotoxin in vitro was found to be a consequence of the anticoagulant employed in collecting the plasma. Addition of calcium to plasma suppressed the activity of its endotoxm detoxifying component (EDC) whereas the addition of calcium-binding anticoagulants rendered serum comparable to plasma. Dialysis of plasma resulted in a marked reduction of its EDC activity despite the concommittant elimination of calcium. EDC activity could then be fully restored upon the addition of calcium-binding anticoagulants. Resin-treated plasma, without added anticoagulant, had EDC activity equal to plasma obtained with calcium-binding anticoagulants. Following dialysis, resin-treated plasma also sustained a marked reduction in EDC activity which could be fully restored by calcium-binding anticoagulants. Restoration was also obtained with the dialysate even after ashing. These findings indicated that the suppression of EDC activity by calcium is not direct but is mediated through its effects on an anionic component of plasma which is required for inactivation of endotoxin by EDC.