Characteristics of Endotoxin Altering Fractions Derived from Normal Human Serum

Alcoholic fractionation of normal human defibrinated plasma by Cohn's method 10 resulted in two fractions capable of altering bacterial endotoxins. Incubation of endotoxin in the first, Fraction IV1, resulted in a marked reduction of the ability of specific antiserum to precipitate endotoxin. In addition, the capacity of the lipopolysaccharide to elicit a pyrogenic response in rabbits was abolished. A second fraction, III0, as isolated, was generally incapable of such effects unless it was activated by several procedures. All other fractions did not affect these properties of endotoxin. Alteration of the lethal activity of endotoxin was not evident after incubation in Fraction IV1, but was reduced after exposure to activated Fraction III0. The characteristics of these reactions are recorded.