Properties of free endotoxin from Pasteurella multocida

Free endotoxin (FET) from virulent encapsulated Pasteurella multocida or from an avirulent nonencapsulated mutant is capable of inducing active immunity, but the lipopolysaccharide (LPS) moiety of the endotoxin is not. These results suggest that a protein of P multocida is involved in the stimulation of active immunity. The serologic specificity of the FET is associated with the LPS moiety, which is related to a heat extracted antigen that is used for serotyping P multocida. The FET is capable of producing widespread vascular alteration and death. It is present in the vascular system of turkeys with acute fowl cholera, and it can be detected with the "Limulus" test for endotoxins and with the gel diffusion precipitin test.