Inhibition by Lipoid A of Formation of Antibodies Against Common Antigen of Enterobacteriaceae.

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Abstract
Summary Five preparations of lipoid A, obtained from highly purified lipopolysac-charides (endotoxins), were shown to inhibit the antibody response to the common antigen (CA) of enteric bacteria. This inhibition occurred when mixtures of antigen and lipoid A (100 μg per injection) were prepared in ethanol in vitro and then redissolved in water for immunization. Only one of these 5 preparations was markedly effective as inhibitor when mixtures of lipoid A and antigen were prepared in vitro in aqueous solution. Quantitation of one of the preparations showed that as little as 20 μg per injection of lipoid A decreased, but did not abolish, the antibody response. Simultaneous injection of antigen and lipoid A into different veins failed to interfere with CA antibody formation. Lipoid A also interferes with the antibody response, when mixtures prepared in ethanol were injected into the footpad with Freund's adjuvant or in the presence of autologous erythrocytes. It is concluded that lipoid A interacts with CA and that antibody formation is suppressed as a result of this interaction.