Immunoglobulin G Subclass Profile of Anticitrullinated Peptide Antibodies Specific for Epstein Barr Virus-derived and Histone-derived Citrullinated Peptides

Abstract

To the Editor: Studies have shown that the anticitrullinated peptide antibodies (ACPA) response is highly polyclonal, in terms of epitope specificity, V genes, and isotype usage1,2. Longitudinal studies of patients with rheumatoid arthritis (RA) have documented epitope spreading, and ACPA, specific for distinct citrullinated epitopes, have been described. By using different citrullinated antigens, ACPA from immunoglobulin (Ig)G, IgA, and IgM isotype have been detected3. ACPA are polyclonal in the usage of different IgG subclasses, but in this case the pattern is more heterogeneous. So far the studies conducted indicate the dominance of IgG1 and IgG4, while IgG3 have been detected with cyclic citrullinated peptide (CCP) and vimentin, but not with fibrinogen4,5. The production of specific IgG subclasses might help in deciphering the mechanisms eliciting B cell expansion in response to different antigens. Thus, it is of interest to explore the profile of IgG subclasses of antibodies reactive with novel citrullinated substrates, already known to be tools for ACPA detection. Ninety-three patients with RA, 25 with psoriatic arthritis, 15 with ankylosing spondylitis, and … Address correspondence to Professor P. Migliorini, Department of Clinical and Experimental Medicine, University of Pisa, Via Roma 67, 56126 – Pisa, Italy. E-mail: paola.migliorini{at}med.unipi.it