Identification of Natural Bispecific Antibodies against Cyclic Citrullinated Peptide and Immunoglobulin G in Rheumatoid Arthritis

Abstract

BackgroundPrevious studies indicate that natural bispecific antibodies can be readily produced in vivo when the body is simultaneously stimulated with 2 distinct antigens. Patients with rheumatoid arthritis (RA) usually exhibit persistent immune responses to various autoantigens, raising the possibility that natural bispecific antibodies against 2 distinct autoantigens might exist.Methodology/Principal FindingsWe identified the presence of natural bispecific antibodies against cyclic citrullinated peptide (CCP) and immunoglobulin G (IgG) in RA patients' sera by means of a double-antigen sandwich enzyme-linked immunosorbent assay (ELISA). The spontaneous emergence of bispecific antibodies was confirmed by mixing different proportions of 1 anti-CCP-positive serum and 1 rheumatoid factor (RF)-positive serum in vitro. Among the tested samples, positive correlations were found between the presence of bispecific antibodies and both IgG4 anti-CCP antibodies and IgG4 RF (r = 0.507, p<0.001 and r = 0.249, p = 0.044, respectively), suggesting that the IgG4 subclass is associated with this phenomenon. Furthermore, bispecific antibodies were selectively generated when several anti-CCP- and RF-positive sera were mixed pairwise, indicating that factors other than the monospecific antibody titers may also contribute to the production of the natural bispecific antibodies.Conclusions/SignificanceWe successfully identified the presence of natural bispecific antibodies. Our results suggest that these antibodies originate from anti-CCP and RF in the sera of RA patients. The natural occurrence of bispecific antibodies in human diseases may provide new insights for a better understanding of the diseases. Further investigations are needed to elucidate their precise generation mechanisms and explore their clinical significance in disease development and progression in a larger study population.

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

“…IgG4 are considered noninflammatory antibodies produced after prolonged immune stimulation. However, pathogenic IgG4 have been described in bullous diseases 8 and bispecific antibodies bearing both rheumatoid factor and ACPA activity have been detected in RA 9 . The lack of correlation between IgG4 and IgG1 suggests further that a different mechanism of induction exists in the 2 antibody subclasses, IgG4 being considered Th2-dependent and IgG1 Th1-dependent.…”

Interleukin-6 Receptor Blockade Selectively Reduces IL-21 Production by CD4 T Cells and IgG4 Autoantibodies in Rheumatoid Arthritis

“…IgG4 does not fix complement and has no strong affinity for FcγR. However, studies have shown that IgG4 is associated with the presence of natural bispecific antibodies against CCP in RA 52, 53. We can speculate that bispecific Abs may be more pathogenic due to crosslinking of different molecules.…”

Value of serum IgG4 in the diagnosis of IgG4-related disease and in differentiation from rheumatic diseases and other diseases

“…The values of IgG4-ACPA in RA were significantly decreased after treatment with TNF blockade [39]. Thus, it is possible that the decline in serum IgG4 in RA is due to disease remission [40]. We continued to analyze the serial changes in IgG4 after therapy in the RA cases.…”