An illustrative example of a case of FL to reveal the nature and structure of the glycan-modified IGV region. (A) Site-specific glycan composition was determined by liquid chromatography–mass spectrometry, and oligomannoses at N38 in CDR-1 of the Ig heavy chain (HCDR1) are depicted in green. There were no sites in the Ig light chain. The gray circle at the GL position N57 indicates no detectable glycan addition. (B) Crystals of the derived Fab′ were analyzed at 1.65 Å resolution, and HCDRs are colored as indicated. The glycan is shown as 2 resolved N-acetyl glucosamine residues at position N38, which are attached to oligomannoses. More detail is available in the article by Chiodin et al.¹³ HC, heavy chain; LC, light chain.