Alpha-1-acid glycoprotein (AGP) is a plasma glycoprotein produced by the liver that undergoes increased production and altered glycosylation in several physiological and pathological conditions including rheumatoid arthritis. To date, although present in the synovial fluid of rheumatoid arthritis patients, there has been no evidence for the separate extra-hepatic production of AGP. This study indicates that there could be a localized production of AGP in rheumatoid synovial fluid by demonstrating that the glycosylation patterns of AGP differed between the serum and synovial fluid in the same rheumatoid patient. Serum AGP was largely composed of fucosylated tri- and tetra-antennary oligosaccharide chains while the synovial fluid contained mainly bi-antennary chains that were fucosylated to a lesser extent. This structural heterogeneity of glycosylation resulted in functional diversity; serum but not synovial AGP is able to inhibit binding to the cell adhesion molecule E-selectin through expression of antigen sialyl Lewis X.
- epithelial cells