The mitogenic, immunogenic and tolerogenic properties of dextrans and levans. Lack of correlation according to differences of molecular structure and size.

The mitogenicity of dextrans, levans and some of their depolymerized fractions was assayed using spleen cells from CBA mice and compared with their immunogenic and tolerogenic potency . Two branched dextrans (B1355 and B1299) induced a greater increase in DNA synthesis than linear dextran B512 which was only feebly mitogenic. The activity of B1355 was greater than that of B1299 and induced a level of stimulation similar to that of polyanions (dextran sulphate and polystyrene sulphonic acid). Dextrans B1355 and B1299 were relatively poor tolerogens for the α1–6 glucosyl epitope whilst the native linear dextran B512 was much more effective. Their immunogenicity for this specificity also decreased in the order B512, B1355, B1299. All depolymerised fractions of B512 induced only minimal mitogenic responses bearing no relevance to their immunogenic and tolerogenic potentials, which declined in parallel with decreasing molecular weight to extinction at 2×10. Native levan, hydrolyzed fractions of it and perennial rye grass fructosans were all equally potent mitogens irrespective of their molecular weight. In contrast, the controlled hydrolysis of levan can, according to extent, abrogate either both its immunogenicity and tolerogenicity or immunogenicity alone. These results together seem incompatible with the hypothesis that discrimination between immunity and tolerance induced by T-independent antigens depends on the intensity of mitogenic stimulation to which they subject corresponding specific B cells.