A humoral substance which inactivates endotoxin in vitro has been shown to be clearly distinguishable from complement, properdin, and specific antibody. For the present, it is designated "endotoxin-detoxifying component" or EDC.
Animal species could be grouped in three categories with regard to the EDC activity of their sera; rat serum was highly potent; chimpanzee, dog, horse, and guinea pig sera were much less active; mouse, rabbit, and sheep sera exhibited no activity. The EDC potency of human sera varied widely, ranging from high to barely discernible activity. In contrast to the variations of EDC potency in serum, citrated plasma from all species manifested high potency of about the same magnitude.
The influence of time, temperature, pH, and concentration of reactants on the inactivation of endotoxin by EDC was examined. EDC activity in plasma and serum was found to be labile to beating at 56°C. for 1 hour. Bacterial endotoxins, derived by different isolation procedures from smooth and rough Gram-negative species, varied considerably in susceptibility to EDC action.