Glycosylation Analysis of Lupus Anti-DNA Antibodies (GALA)

Systemic lupus erythematosus (SLE) is a severe autoimmune disease in which patients often develop numerous autoantibodies (Abs). Unfortunately, none of the SLE specific Abs described so far (anti-DNA, -C1q, -nucleosome) are correlated enough to the disease activity to be used as a useful biomarker and reliably help in the therapeutic decision. Abs effector functions, including antibody-dependent cell-mediated cytotoxicity (ADCC), antibody-dependent cellular phagocytosis (ADCP) and antibody-mediated complement activation, are conditioned by the structure of the crystallizable fragment (Fc) and especially the N-linked oligosaccharide structures attached to the asparagine-297 in the CH2 domain of the Fc region. It has been shown that the decrease in galactosylation, sialylation and fucolylation is generally associated with inflammatory function of circulating IgG whereas Abs with sialic acid, fucose and/or galactose in Asn-297 are anti-inflammatory. This major role of Ab glycosylation in the regulation of the effector and pathogenic functions of Abs have been well documented in rheumatoid arthritis and ANCA associated vasculitis with a good correlation between Ab sialylation and disease activity. In lupus, it has been shown that glycosylation of total IgG is also altered and correlated with disease activity but glycosylation analysis of the LES specific Abs is still lacking. The aim of this study is to analyse by mass spectrometry (MS) the different glycoforms of anti-DNA Abs in lupus patients and find a correlation with disease activity.

140 adult patients with lupus and anti-DNA Abs will be prospectively recruited in the University Hospital of Montpellier and Nîmes (department of rheumatology, internal medicine and nephrology) and followed during 1 year. Blood samples will be drawn at inclusion, at 1 year and during any flare of the disease. After centrifugation (2000g x 10 minutes) serum will be aliquoted and frozen at -80°C. At the end of the study, total IgG will be isolated using protein G and anti-DNA Abs will be purified from total IgG with DNA affinity columns. Glycosylation status of the anti-DNA Abs will be extensively determined by mass spectrometry and correlated to disease activity (SLEDAI).