Glycobiology of immunoglobulin G

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Although the galactose deficiency in the Asn297-linked sugar chains of serum lgG from patients with rheumatoid arthritis has been established, structural analysis of sugar chains has not readily available.Psathyrella velutina lectin (PVL) preferentially interacts with the N-acetylglucosaminebeta1*2Man group, exposed at the termini of sugar chains in agalacto lgG.An ELISA-based assay for the detection of agalacto lgG was developed.PVL binding of serum lgG signifilcantiy correlated with percentage of galactose-deficient lgG.Age-related slight increase in PVL binding was observed.PVL binding was significantly higher in the synovial fluid compared with paired serum samples.This assay system may provide an ideal tool for the simple and sensitive detection of agalcto lgG.The structure of the N-linked sugar chains attached to three lgG antibodies, identical in amino acid sequence except for the change required to introduce the carbohydrate addition sites, has been determined.All three antibodies are specific for dextran but differ in their ability to bind antigen.In addtition to the glycosylation site in the Fc portion, each antibody has a different glycosylation site in the second complementarity determining region (CDR2) of the heavy chain.The variable region carbohyrate structures attached at Asn54 and Asn58 were complex-type but that at Asn60 was a high mannose structure.These results demonstrate that slight changes in the position of carbohydrate attachment within CDR2 of the variable region of the heavy chain can substantially alter carbohydrate processing and that complex-type carbohydrates contained within the same polypeptide chain can have different structures.These alterations in carbohydrate structure can have significant consequences on the biological properties and potential usefulness of recombinant antibodies.