Preparation of dextran-protein conjugates and studies of their immunogenicity.

Abstract

The preparation of soluble conjugates between dextran M<sub>w</sub> 4,400 and several proteins by the cyanogen bromide method is described. Conjugates were purified by ultrafiltration and characterized by gel chromatography; their polysaccharide content varied from 3.5 to 31%. Such dextran-protein conjugates proved strongly immunogenic in rabbits, sheep and guinea pigs, when given repeatedly in complete Freund’s adjuvant in doses of 0.5 mg/animal. Dextran-specific antibodies could be demonstrated by heterologous PCA, passive hemagglutination, reversed single radial immunodiffusion, and quantitative precipitation. In rabbit and sheep antisera, average specific antidextran concentrations of 1–3.6 mg/ml were obtained. On prolonged immunization, the antibody level remained rather constant. The weak immunogenicity of homopolymers is discussed and several procedures allowing to increase their immunogenicity are reviewed. The importance of protein coupling for raising antibodies against oligo- and polysaccharides is stressed.