Differences in IgG Sialylation Distinguish Asymptomatic from Symptomatic Anti-Nuclear Antibody Positive Individuals.

Abstract

OBJECTIVE The transition from asymptomatic anti-nuclear antibody (ANA) positivity to systemic autoimmune rheumatic disease (SARD) is associated with increased production of pro-inflamamtory factors such as TNF-α. Here we investigate whether the relative absence of inflammation in asymptomatic ANA+ individuals (ANA+NS) results from a lack of circulating immune complexes (ICs) or from changes in the characteristics of the IgG auto-Abs produced. METHODS Flow cytometry was used to characterize circulating microparticles (MPs) in 18 healthy controls (ANA-HC), 31 ANA+NS and 51 symptomatic ANA+ patients. Differences in the ability of the total MPs, purified IgG-coated MPs, or aggregated IgG to elicit inflammation were investigated by co-culture with ANA-HC monocytes or monocyte derived dendritic cells (moDC), measuring cytokines in the supernatants. IgG sialylation was quantified by ELISA or lectin blotting using Sambucus Nigra Agglutinin, a sialic acid-binding lectin. RESULTS All ANA+ individuals had higher numbers of total and IgG-coated MPs than ANA-HC. IgG sialylation was significantly reduced in SARD compared to ANA+NS and ANA-HC, and in ANA+NS who clinically progressed in the next 2 years compared to those who did not. moDC stimulated with IgG-coated MPs or aggregated IgG from SLE patients produced significantly more TNF-α than those from ANA+NS. The levels of TNF-α produced in culture supernatants and serum demonstrated a negative correlation with IgG sialylation. CONCLUSIONS The absence of pro-inflammatory factors in ANA+NS does not result from a lack of circulating ICs, but instead may reflect differences in the extent of IgG sialylation in the ICs from ANA+NS as compared to SARD.