Inactivation by polymyxin B of the endotoxin-mediated interferon production in the rabbit.

Polymyxin B (PB) completely or at least significantly inhibited the capacity of Shigella dysenteriae 1 cells and the lipopolysaccharide (LPS) and lipid A (LA) subunits of several bacterial endotoxins to induce interferon (IFN) in rabbits. Animals injected with LPS inactivated by PB to the point of not inducing detectable IFN levels did not develop hyporesponsiveness to secondary IFN induction by a homologous inducer. It was concluded that PB inhibits the IFN-inducing capacity of endotoxin and its subunits as a consequence of binding to the LA-moiety of LPS. The results confirmed the exclusive role of LA as the only IFN-inducing component of Gram-negative bacterial endotoxin.