Four BALB/c IgA mouse myeloma proteins (W3129, W3434, QUPC 52, and UPC 102) reactive with dextran, four myeloma proteins reactive with fructosans, three IgA (W3082, UPC 61, and Y5476), and one IgG2a (UPC 10), and two human antilevans were studied immunochemically. Quantitative precipitin and inhibition assays showed that W3129, W3434, and QUPC 52 had specificities for isomaltose oligosaccharides similar to those previously found with α(1 → 6)-specific human antidextrans. W3129 and W3434 were most complementary to IM5 but W3129 reacted equally with IM4 and IM3 while W3434 had a greater affinity for IM4 than IM3. QUPC 52 had a larger combining region and was most complementary to IM6. Protein UPC 102 (IgA), like MOPC 104E (IgM) (27), was most complementary to the α(1 → 3)-linked trisaccharide, nigerotriose, and thus differed from J558 (29), which was inhibited best by nigeropentaose. UPC 102 was similar to J558 but they differed from MOPC 104E in their reactions with non-α(1 → 3)-linked disaccharides.
The fructosan-specific myeloma proteins fell into two groups with different specificities. The first group, W3082 (IgA), UPC 61 (IgA), and the previously studied J606 (IgG3) (28, 29), reacted with inulin and W3082 and UPC 61 appeared to have identical specificities for ß(2 → 1)-linked fructofuranosyl residues with maximum complementarity for the tetrasaccharide ßDfructofuranosyl (2 → 1)ßDfructofuranosyl(2 → 1)ßDfructofuranosyl(2 → 6)Dglucose while protein J606 was inhibited best by the trisaccharide ßDfructofuranosyl(2 → 1)ßDfructofuranosyl(2 → 6)Dglucose. W3082 and UPC 61 also differed from J606 in their behavior toward sucrose and ßDfructofuranosyl(2 → 6)Dglucose as compared with αDglucosyl(1 → 3)Dfructose (turanose). The second group containing myeloma proteins UPC 10 (IgG2a) and Y5476 (IgA) behaved similarly to human antilevans in that neither reacted with inulin nor were they inhibited by the ß(2 → 1)-linked fructose oligosaccharides. Unlike the ß(2 → 1)-specific proteins, they reacted with perennial rye grass levan that contained over 90% ß(2 → 6)links. The differences in specificity and site size among homogeneous mouse myeloma proteins reactive with the same antigenic determinant are completely consistent with the concept that they represent products of homogeneous clones selected from the known heterogeneous population of antibody-forming cells.