The immunological properties of typhoid endotoxin were investigated after incubating it with serum under conditions in which EDC (endotoxin-detoxifying component) was operative. Brief interaction of endotoxin in vitro with this system in serum (human, rabbit, mouse) abolished its antigenicity for rabbits. Suitable modification of the host permitted separate elicitation of toxic and antigenic responses to typhoid endotoxin. Endotoxin altered by EDC was still capable of precipitating specific antibody; moreover, it did so in a manner which resembled that of the haptenic polysaccharide.

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