Immunity to cholera: relation of fraction II of type 2 cholera toxin to vibriocidal antibody.

The nontoxic protein component in supernatant fluids of young cultures of the cholera vibrio in peptone dialysate broth contains an antigen identical in specificity to vibrio lipopolysaccharide. This material was heterogeneous after elution from diethylaminoethyl A50 Sephadex, and it contained at least five additional minor antigens. Identity was demonstrated by immunodiffusion methods, by the induction of specific vibriocidal antibody formation, and by specific interference in the vibriocidal reaction. The minor antigens appeared to be unrelated to the vibriocidal reaction. The major antigen was more highly immunogenic than lipopolysaccharide, giving higher and longer-persisting antibody titers in the rabbit, but lipopolysaccharide was the more effective interfering antigen per unit weight in the vibriocidal reaction. The nontoxicity and high immunogenic potency of the protein antigen suggest that it may be useful as an immunizing agent for the production of the antibacterial component of an effective immunity.