Immunochemical Studies on Dextrans

Abstract

Abstract Rabbits were immunized with a hapten-protein conjugate corresponding to a terminal nonreducing chain of five α(1 → 6) linked glucose units plus an additional α-linkage to a six carbon open sugar chain. The antigen was prepared by oxidizing isomaltohexaose to isomaltohexaonic acid and coupling it to bovine serum albumin (BSA). Antisera cross-reacted with dextrans, the amount of dextran required for maximum precipitation being related to its content of α(1 → 6) linkages. This cross-reaction was independent of anti-BSA. Inhibition studies with the isomaltose oligosaccharides from the tri-(IM3) to hepta-(IM7) or octa-(IM8) saccharide with the six antisera showed that four had combining sites complementary to IM6 and two to IM5. For the four sera IM6, IM7, and IM8 were equally effective as inhibitors on a molar basis, better than IM5, IM4 and very much better than IM3. For the remaining two sera IM5, IM6, and IM7 were equivalent and gave better inhibition than IM4 and IM3. Inhibition studies using the aldonic acids series from IM4-COOH to IM7-COOH showed five sera to be maximally inhibited by the pentaonic acid (IM5-COOH) which corresponded to the inhibition obtained with IM6 to IM8 in three sera. The two sera that were maximally inhibited by IM5 showed better inhibition with IM5-COOH and higher members of this series. The last serum showed unique behavior, better inhibition being obtained with the hexasaccharide than with any of the acids. Inhibition by IM4-COOH was equivalent either to IM4, to IM3, or was intermediate for all sera. In one case the IM5-COOH was equivalent to IM4-COOH and IM4. Thus heterogeneous populations of antibodies were formed in each serum as indicated by differences in the relative ease with which inhibition with large and small oligosaccharides and their corresponding acids was obtained.