In vitro neutralization of the Shwartzman-inducing activity of endotoxins by immune serum

The Shwartzman-inducing activity in rabbits of purified endotoxin from four O serotypes of Escherichia coli, one strain of Salmonella typhi and one of Serratia marcescens was completely abolished by mixture, before intradermal injection, with homologous rabbit antiserum. The neutralization was highly specific since the same sera had no effect, under the conditions used, on endotoxin of heterologous serotypes or heterologous species. Neutralization of inducing activity did not require incubation or complement and was demonstrable independently of the species of endotoxin used for provocation. Inducing activity could be restored by extraction of the endotoxin—antiserum mixture with aqueous phenol, but not with trichloracetic acid.