Background/Purpose: The nuclear oncoprotein DEK is a known autoantigen associated with juvenile idiopathic arthritis (JIA) and other autoimmune diseases.  DEK is actively secreted by human macrophages and is a chemoattractant for neutrophils and T cells. We have previously demonstrated that DEK and DEK autoantibodies are abundant in inflamed synovia of JIA patients. Posttranslational modification, especially acetylation, increases DEK’s antigenicity substantially.  In agreement with previous observations by Szer et al., our studies of the nature of DEK autoantibodies have shown that autoantibodies from JIA patients recognize the DEK C-terminal region.  By screening 69 serum samples, including those from 38 patients with JIA, 20 patients with other inflammatory conditions, and 11 samples from healthy controls, we show that the C-terminal 25 amino acids (aa) alone is the most essential site for DEK antigenicity.

Methods: Sera were collected from patients being treated for JIA and other rheumatologic diseases in the Pediatric Rheumatology Division at the University of Michigan.  Samples were analyzed by a specific ELISA developed in our laboratory for the detection of DEK antibodies. Recombinant DEK His-tagged proteins, including full length(1-375aa), and partial length (187-375aa and 1-350aa) proteins were made in a baculovirus system, and were used as the antigen for ELISA and immunoblotting.   In addition, we inserted DEK’s C-terminal 25aa domain into a GST vector to be expressed by E. coli with subsequent purification.  ELISA results were calculated as area under the curve (AUC) by Simpson Rule.

Results: ELISA results showed significantly higher levels of DEK autoantibodies in sera of JIA patients compared to patients without JIA (p=0.01) or healthy controls (p=0.001).  Immunoblot screening against full length DEK (1-375aa), the DEK C-terminus 25aa (position 350-375), and full-length DEK minus the last 25 amino acids (1-350aa) confirms that DEK’s most immunogenic portion consists of the C-terminal 25aa. These results were also corroborated by expression of DEK’s C-terminal 25aa alone.

Conclusion: We have previously demonstrated presence of DEK and DEK autoantibodies in joints of JIA patients, resulting in development of immune complexes that contribute to joint inflammation. In addition, DEK plays an active role in recruiting neutrophils to joints, as well as in formation of neutrophil extracellular traps (NETs).  Our current data suggests that the C-terminal 25aa is the most immunogenic portion of DEK. This finding has significant importance with respect to future development of specific diagnostic tools for JIA, as well as for new strategies to eliminate DEK autoantibodies.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/deks-autoantigenicity-in-juvenile-idiopathic-arthritis-resides-in-its-c-terminal-25-amino-acids/