A longitudinal study of the relationship between galactosylation degree of IgG and rheumatoid factor titer and avidity during long-term immunization of rabbits with BSA

Increased concentration of two different advanced glycation end-products detected by enzyme immunoassays with new monoclonal antibodies in sera of patients with rheumatoid arthritis

Background

Levels of pentosidine (representative of advanced glycation end-products) in sera of patients with rheumatoid arthritis are increased when compared with sera of other diagnoses or healthy controls. These levels have been reported to correlate with clinical indices of rheumatoid arthritis activity and with laboratory markers of inflammation. The purpose of this study was to find out if these findings pertain to other advanced glycation end-products.

Methods

We have developed two immunoassays based on new monoclonal antibodies to advanced glycation end-products. Antibody 103-E3 reacts with an unidentified antigen, formed in the reaction of proteins with ribose, while antibody 8-C1 responds to N^ε-(carboxyethyl)lysine. We have used these monoclonal antibodies to measure levels of advanced glycation end-products in sera of patients with rheumatoid arthritis, systemic lupus erythematosus, osteoarthritis, and healthy controls. We calculated the correlations between advanced glycation end-product levels in rheumatoid arthritis sera and the Disease Activity Score 28 (DAS28), age, disease duration, CRP, anti-CCP, rheumatoid factor and treatment with corticosteroids, respectively.

Results

Levels of both glycation products were significantly higher in sera of patients with rheumatoid arthritis when compared with sera of patients with systemic lupus erythematosus, osteoarthritis, or the healthy controls. Neither the level of N^ε-(carboxyethyl)lysine nor the level of the 103-E3 antigen in rheumatoid arthritis sera correlated with the DAS28-scored rheumatoid arthritis activity. The levels of both antigens in rheumatoid arthritis sera did not correlate with age, gender, corticosteroid treatment, or levels of CRP, anti-CCP antibodies, and rheumatoid factor in sera.

Conclusions

We report highly specific increases in the levels of two advanced glycation end-products in sera of patients with rheumatoid arthritis. This increase could be explained neither by rheumatoid arthritis activity nor by inflammation. We propose a working hypothesis that presumes the existence of a link between advanced glycation end-product formation and induction of autoimmunity.

The crystal structure of rabbit IgG-Fc

We report the structure of the Fc fragment of rabbit IgG at 1.95 A (1 A=0.1 nm) resolution. Rabbit IgG was the molecule for which Porter established the four-chain, Upsilon-shaped structure of the antibody molecule, and crystals of the Fc ('Fragment crystallisable') were first reported almost 50 years ago in this journal [Porter, R. R. (1959) Biochem. J. 73, 119-126]. This high-resolution analysis, apparently of the same crystal form, reveals several features of IgG-Fc structure that have not previously been described. More of the lower hinge region is visible in this structure than in others, demonstrating not only the acute bend in the IgG molecule that this region can mediate, as seen in receptor complexes, but also that this region has a tendency to adopt a bent structure even in the absence of receptor. As observed in other IgG-Fc structures, the Cgamma2 domains display greater mobility/disorder within the crystals than the Cgamma3 domains; unexpectedly the structure reveals partial cleavage of both Cgamma2 intra-domain disulphide bonds, whereas an alternative conformation for one of the cysteine residues in the intact bridge within the more ordered Cgamma3 domains is observed. The N-linked oligosaccharide chains at Asn(297) are well-defined and reveal two alternative conformations for the galactose units on each of the alpha(1-6)-linked branches. The presence of this galactose unit is important for stabilizing the structure of the entire branched carbohydrate chain, and its absence correlates with the severity of autoimmune conditions such as rheumatoid arthritis in both human clinical studies and in a rabbit model of the disease. Rabbit IgG, through this high-resolution structure of its Fc region, thus continues to offer new insights into antibody structure.

Hypogalactosylation of Salivary and Gingival Fluid Immunoglobulin G in Patients With Advanced Periodontitis

BACKGROUND

Altered glycosylation of immunoglobulin G (IgG) has been found to affect certain immunological activities of IgG and to correlate with increased inflammation in various disease states. This work deals with the changes in distribution and galactosylation of IgG subclasses present in saliva and gingival crevicular fluid (GCF) of patients with initial and advanced periodontitis and of normal controls.

METHODS

IgG subclasses were quantified by dot-blot assay, and the degrees of expression of galactose in the total IgG and its individual subclasses were estimated by lectin immunoblot assay after sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) separation of IgG and by capture enzyme-linked immunosorbent assay (ELISA), using biotinylated Ricinus communis (RCA-I) and Bandeiraea simplicifolia (BS-II) lectins.

RESULTS

The distribution of IgG subclasses in both fluids was found to differ in periodontal patients compared to normal controls. In the periodontitis saliva and GCF, the IgG2 subclass dominated quantitatively, regardless of periodontal status. However, galactose was found to be expressed in IgG heavy chains in normal controls and patients with initial periodontitis but not, or at barely detectable levels, in advanced periodontitis.

CONCLUSION

The results suggest that the shift toward hypogalactosylated glycoforms may occur during the process of inflammation of the gingiva.