SPECIFIC FRACTIONATION OF HUMAN ANTIDEXTRAN ANTIBODIES

Abstract

Antidextran of one individual, absorbed specifically on sephadex, was fractionated into two populations of antibody molecules by successive elution with oligosaccharides of the isomaltose series of increasing size. Purified fractions and some human antidextran sera fixed complement with dextrans of molecular weight of 195,000 and above. Quantitative micro-complement fixation inhibition assays showed that antibody eluted with isomaltotriose had a higher affinity for smaller oliogosaccharides relative to isomaltohexaose, indicating a high content of antibody molecules with smaller combining sites, while with the second fraction, eluted with isomaltohexaose, the small haptens were very poor inhibitors. These differences appear to be related to the sizes of the antibody combining sites. The fraction with molecules with smaller size-combining sites fixed only about half as much complement per unit antibody N as did. the second fraction with larger combining sites, suggesting that the strength of complement fixation is affected by the strength of the antigen-antibody interaction.