Extensive glycosylation of ACPA-IgG variable domains modulates binding to citrullinated antigens in rheumatoid arthritis.

Objectives: To understand the molecular features distinguishing anti-citrullinated protein antibodies (ACPA) from 'conventional' antibodies in rheumatoid arthritis (RA).

Methods: Serum of ACPA-positive RA patients was fractionated by size exclusion chromatography and analysed for the presence of ACPA-IgG by ELISA. ACPA-IgG and non-citrulline-specific IgG were affinity purified from serum, plasma and/or synovial fluid and analysed by gel electrophoresis.

The fine specificity of IgM anti-citrullinated protein antibodies (ACPA) is different from that of IgG ACPA.

Introduction: The antigen recognition pattern of immunoglobulin M (IgM) could, when directed against protein antigens, provide an indication of the antigenic moieties triggering new B cells. The half-life of IgM is short and memory B cells against T-cell-dependent protein antigens typically produce IgG and not IgM antibodies. In this study, we analyzed whether a difference exists between the fine specificity of IgM versus IgG anti-citrullinated protein antibodies (ACPAs).