Identification of genes for variable regions of immunoglobulins that recognize sialylated glycans

We previously reported an antibody (clone ID: FR9, IgM-κ) that recognizes the sialyl oligosaccharide Neu5Acα2,6Galβ1,4GlcNAc as an epitope on glycoproteins and glycolipids. In the present study, we developed an antibody (clone ID: AFR45, IgM-κ) that recognizes Neu5Acα2,3Galβ1,4GlcNAc/Glc as an epitope on glycoproteins and glycolipids and compared the nucleotide and amino acid sequences of the immunoglobulin gene variable regions with those of FR9. The heavy chain variable (V_H) regions of FR9 and AFR45 were encoded by different V_H gene segments, each of which was composed of a characteristic D gene segment. The major differences between V_H genes encoding various antibodies deposited in public databases and FR9 and AFR45 were identified in the D gene segment, indicating that D genes play a critical role in determining the epitope specificity of these antibodies. Surprisingly, although FR9 and AFR45 were obtained independently from different mice immunized with different immunogens, the light chain variable (V_L) region nucleotide sequences were identical. The V_L gene consisted of Igkv4-57 and Igkj4 gene segments (Igkv4-57j4), the sequences of which were identical to V_L genes for a number of antibodies against meningococcal group C capsular polysaccharide deposited in public databases. As this polysaccharide is a sialic acid homopolymer, these results indicate that Igkv4-57j4 encodes a V_L common to immunoglobulins that recognize sialylated glycans.