Immune complexome analysis of antigens in circulating immune complexes isolated from patients with IgG4-related...

IgG4-related disease (IgG4-RD) is characterized by various serological abnormalities. Some patients with IgG4-RD present with hypergammaglobulinemia, hypocomplementemia, and autoantibodies recognizing rheumatoid factors and nuclear factors. However, whether IgG4-RD is an autoimmune disease remains unclear.

Here, we used immune complexome analysis to comprehensively identify constituent antigens of circulating immune complexes isolated from 10 patients with IgG4-related dacryoadenitis and/or sialadenitis (IgG4-RDS) which is one condition associated with IgG4-RD.

We detected each of 125 distinct antigens in independent samples from two or more patients with IgG4-RDS. Of them, 17 antigens were found to be specific to patients with IgG4-RDS by comparing 125 antigens with all the antigens found in other connective tissue diseases (antineutrophil cytoplasmic antibody-associated vasculitis, Takayasu's arteritis, mixed connective tissue disease, dermatomyositis, Sjögren's syndrome, systemic scleroderma, and systemic lupus erythematosus) or healthy donors. The number of disease-specific antigens associated with IgG4-RDS was comparable to those autoimmune diseases.

Studies of the 17 IgG4-RDS-specific antigens might lead to a better understanding of the pathogenesis of IgG4-RD, but further study of the prevalence of these CIC-associated antigens that involves a selective and sensitive assay will be needed to determine their potential as diagnostic or pathogenic biomarkers.