Background/Purpose: Anti-aminoacyl tRNA synthetase (ARS) antibodies are associated with common clinical characters, which are fever, polyarthritis, interstitial lung disease (ILD), Raynaud’s phenomenon, mechanic’s hand and myositis, and the constellation of these symptoms in patients with anti-ARS antibody is called anti-synthetase syndromes (ASS). So far, anti-ARS antibodies have been screened by RNA/ protein immunoprecipitation (IP) or line blot. Recently, an enzyme-linked immunosorbent assay (ELISA), in which the mixture of 5 ARS antigens are coated on the plate, has been established, and growing number of blood samples has been examined in daily clinical practices. However, we often encounter such patients that are positive for anti-ARS antibody by ELISA but negative by IP. Thus, we analyzed the discrepancy between the ELISA and IP precisely to elucidate the underlying mechanism and the clinical meaning of the discrepant results.

Methods: We screened anti-ARS antibodies both by RNA-IP using HeLa cells and ELISA (MESACUP^TM anti-ARS test, MBL CO., LTD., Nagoya, Japan) for sera obtained from patients who visited to our department with suspicion of rheumatic diseases from January 2014 to March 2017. The sera which showed discrepant results between two methods were further analyzed by individual antigen-specific ELISA, immunoblotting, and protein-IP. Obtained results were compared to see the discordance among different methods. The clinical features of the patients were also characterized.

Results: Eleven patients (6 females and 5 males with mean age of 67.3±12.4 years-old) were found to be positive for anti-ARS by the ELISA but negative by RNA-IP. The clinical diagnoses were 2 RA, 2 SSc, 1 SS, 1 DLE, 1 PM with SS, 1 DM and 3 unclassified ILD. Within these 11 patients, anti-Jo-1 antibody was detected by specific ELISA in 9 patients, but only in 5 and 1 by protein-IP and immunoblot, respectively. On the other hand, anti-EJ antibody was detected in 5 patients by immunoblot, and some of these sera were considered to cross-react to Jo-1 antigen by absorption ELISA using each antigen. Ten (91%) patients presented ILD, which responded to glucocorticoids without recurrence, while, numbers of patients presented other ASS symptoms were as follows; 3 (27%) mild myositis, 4 (36%) polyarthritis, 5 (45%) Raynaud’s phenomenon, 1 (9%) mechanic’s hand, and 0 (0%) fever.

Conclusion: Positivity of anti-ARS antibodies sometimes shows discrepancy between ELISA and IP, and it may be due to the recognition of denatured or cryptic ARS epitopes by the antibodies. In such cases, anti-ARS antibodies can be associated more strongly with ILD than with myositis. However, we need to further follow up these patients to investigate whether epitope spreading may occur, which leads to the onset of established myositis with positive anti-ARS antibodies not only by ELISA but also by IP.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/clinical-significance-of-anti-aminoacyl-trna-synthetase-antibodies-which-are-positive-by-elisa-but-not-by-immunoprecipitation-the-variations-of-antigen-recognition-and-the-association-with-i/