Differential Effects on Immunogenicity and Antigenicity of Heat, Freezing and Alkali Treatment of Bacterial Antigens

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Abstract
Heating, freezing and treatment with alkali of common enterobacterial antigen and of endotoxic lipopolysaccharides obtained by the aqueous ether procedure strikingly affected their immunogenicity (antibody response of the rabbit), but not their antigenicity (antibody-neutralizing capacity). Immunogenicity of these antigens was reduced by more than 90% by heating for 1 hr at 100°C or treatment with 0.25 N NaOH. Immunogenicity was restored to a significant degree after repeated freezing (-20°C) and thawing of heated antigen and to a lesser degree after alkali treatment. Antibody-neutralizing capacity remained unaffected by these measures. Lipopolysaccharides extracted by the phenol-water procedure had poor immunogenicity, which was affected only slightly by heating or freezing. Immunogenic lipopolysaccharides consisted of two fractions separated by Millipore filtration (0.22 µ); the aggregated fraction engendered antibodies readily and the soluble fraction did not. Heated, alkali-treated and filtered preparations of these antigens induced immunologic priming even when antibody production, as measured by the hemagglutination method, was minimal.

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