Immunochemical studies of mouse monoclonal antibodies to dextran B1355S—II. Combining site specificity, sequence, idiotype and affinity

The specificities of the combining sites of 19 mouse monoclonal antibodies to dextran B1355S have been characterized immunochemically by quantitative precipitin and precipitin inhibition assays; association constants for B1355S were determined by affinity gel electrophoresis. Cross-reactive and individual idiotypes related to the BALB/c B1355S-binding myeloma proteins MOPC104E [IdI(MOPC104E)] and J558 [IdI(J558)], determined by a radioimmunoassay, and heavy-chain variable-region sequences, are presented. Antibodies to B1355S are “α(1 → 3)α(1 → 6)-specific” as determined by precipitin and precipitin inhibition assays with dextrans and oligosaccharides, respectively, containing alternating α(1 → 3)α(1 → 6) linkages compared with oligosaccharides composed solely of α(1 → 3) or α (1 → 6) linkages; all antibodies have low association constants (≦ 10 5ml/g). However, there is also considerable diversity among the proteins as seen in the five groups of different patterns of reactivity with numerous dextrans having different structures, and the variability in affinity even among antibodies showing the same fine specificity by precipitin assay. There is little observable correlation of heavy-chain variable-region amino-acid sequence with specificity or affinity; however, all proteins having D-region amino acids Tyr,Asp at positions 96,97 express the MOPC104E individual idiotype and belong to precipitin specificity group 5, the group most cross-reactive with numerous dextrans, whereas those proteins having the J558 individual idiotype, Arg,Tyr or Asn,Tyr at 96,97 are found in all five precipitin groups.