Study on the Molecular Basis of Anti-Citrullinated Peptide Antibodies in the Immunopathogenesis of Rheumatoid Arthritis
Date Issued
2010
Date
2010
Author(s)
Lu, Ming-Chi
Abstract
Rheumatoid arthritis (RA) is an important disease in rheumatology and its prevalence rate is around 1%. It is characterized by chronic symmetric polyarticular synovitis. Persistent joint swelling and inflammation not only caused the deformity of joints but also increased the mortality in RA patients. Althouth there were many studies investigating the pathogenesis of RA, the definite molecular mechanism of chronic synovitis remained to be elucidated. In recent years, the discovery of anti-citrullinated peptide antibodies (ACPAs) was a milestone in RA. Currently ACPAs was the most specific marker autoantibody in RA patients correlating with its disease activity. In addition, the most unique nature of ACPAs is that the autoantibody may appear even before the onset of arthritis. It is conceivable that ACPAs were involved in the pathogenesis of RA; however the definite molecular pathogenesis has not been elucidated. My thesis contains both clinical and basic dimension about ACPAs in the pathogenesis of RA. In clinical setting, we evaluated the usefulness of anti-agalactosyl IgG antibodies〔anti-Gal(0) IgG〕, rheumatoid factors (RF) and ACPAs in the differential diagnosis of different rheumatic disorders mimicking RA. In basic research, we hypothesized that ACPAs may directly bind to cell surface citrullinated proteins to stimulate mononuclear cells to elicite inflammatory reaction.
ACPAs were purified from pooled ACPAs (+) RA sera by cyclic citrullinated peptide (CCP)-conjugated affinity column. After co-culture of U937 cells with ACPAs, the tumor necrosis factor (TNF)-α production and nuclear factor (NF)-κB DNA binding activity of the cells were measured by ELISA. The cognate antigen(s) of ACPAs on the U937 cell surface was probed by ACPAs, and the reactive bands were identified by proteomic analysis.
In clinical setting, ACPAs was the most specific and sensitive biomarker for diagnosis of RA from its mimic. In basic research, ACPAs specifically enhanced TNF-α production and increased DNA binding activity of NF-κB in U937 cells. In contrast, ACPA-depleted RA sera failed to activate U937 cells. Proteomic analysis revealed that glucose-regulated protein 78 (GRP78, 72 kDa) was one of the cognate antigens for ACPAs. GST-tagged recombinant GRP78 could not recognize by ACPAs due to lack of citrullination. In addition, we found that GRP78 was citrullinated on U937 cell surface that rendered its binding activity with ACPAs. The citrullinated GRP78 inhibited ACPA-induced TNF-α production by U937. ACPAs also bound to human monocytes to promote TNF-α production.
In conclusion, the presence of ACPAs was a very useful biomarker for diagnosis of RA. Furthermore, we clearly demonstrated that ACPAs enhanced the NF-κB activity and TNF-α production in monocytes/macrophages via binding to surface-expressed citrullinated GRP78 that involved in rheumatoid pathogenesis.
Subjects
rheumatoid arthritis
anti-citrullinated peptide antibodies
tumor necrosis factor-α
monocytes
glucose-regulated protein 78
SDGs
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