In vivo protection against scorpion toxins by liposomal immunization

The possibility of raising a humoral immune response able to induce protection from the lethal effects of scorpion toxins was evaluated in the mouse model. A toxic fraction from the venom of the scorpion Tityus serrulatus was entrapped in sphingomyelin-cholesterol liposomes which yielded a conveniently detoxified immunogen. After three injections of this immunogen, all but three of a group of 18 mice developed an IgG response which was shown to be both specific and of good affinity for the toxic antigen. In vitro neutralization assays indicated that pre-incubation of a lethal dose of the toxic fraction with immune sera strongly diminished its toxicity. In vivo protection assays showed that mice with the highest levels of circulating anti-toxin antibodies could resist the challenge by double the normal LD₅₀ of the toxic fraction, which killed all control non-immune mice. The protection was, however, found to be limited both in its duration and its effectiveness against higher amounts of toxin.