Background/Purpose : Autoantibodies directed against the aminoacyl transfer RNA (tRNA) synthetases are associated with myositis, arthritis, Raynaud’s phenomenon, mechanic’s hands, fever, and interstitial lung disease, clinically referred to as anti–synthetase syndrome. Targoff and his colleagues reported a case with an autoantibody to tyrosyl–tRNA synthetase (TyrRS) with features of anti–synthetase syndrome at the 2005 ACR meeting. At the 2013 ACR meeting, we reported three more patients with anti–TyrRS autoantibodies in the setting of anti–synthetase syndrome using other assays than previously reported methods: enzyme–linked immunosorbent assay, Western blot, and immunoprecipitation assay. In addition, one of the authors of this abstract reported that TyrRS can be split into two fragments with distinct chemotactic activities: an interleukin-8 (IL-8)–like cytokine, and an endothelial-monocyte-activating polypeptide II (EMAP II)–like cytokine (Science. 1999). We aimed to further elucidate the pathogenic role of TyrRS in anti–synthetase syndrome.

Methods : Previously defined anti–TyrRS antibody–positive patients with features of anti–synthetase syndrome were the study subjects. Anti–TyrRS antibody–positive and control sera were tested for the ability to inhibit TyrRS aminoacylation by preincubation of the enzyme source with the sera. Recombinant human TyrRS and histidyl–tRNA synthetase (HisRS; Jo–1) proteins were generated. Peripheral blood mononuclear cells (PBMCs) were isolated from heparinized whole blood of an anti–TyrRS or an anti–HisRS antibody–positive patient by density gradient centrifugation. Then, PBMCs were cultured and stimulated with TyrRS, HisRS, or phytohemagglutinin (PHA). Antigen–specific cell proliferation was analyzed using tetrazolium salt as a chromogenic indicator for nicotinamide adenine dinucleotide (NADH). Immunohistochemical analyses were performed to determine if the corresponding chemokine receptors were upregulated in frozen muscle tissue from an anti-TyrRS antibody–positive patient using primary mouse anti–human mAbs and peroxidase-conjugated anti–mouse IgG Fab’.

Results : Anti–TyrRS sera significantly inhibited the in vitro enzymatic function of TyrRS (aminoacylation of tRNA^Tyr) compared with normal control serum. In the cell proliferation assay using PBMCs from an anti–TyrRS patient, the O.D. values of the TyrRS–stimulated cells were significantly higher than in those of the unstimulated cells and HisRS–stimulated cells. Immunohistochemical analyses demonstrated that C–C chemokine receptor type 1 (CCR1) and type 2 (CCR2) which are the receptor of IL–8, and type 3 (CCR3) which is the receptor of EMAP II, were expressed in degenerating muscle fibers, vascular endothelial cells, and infiltrating mononuclear cells in muscle tissue from an anti–TyrRS antibody–positive patient.

Conclusion : This study showed that the anti–TyrRS sera can function as an enzyme inhibitor. TyrRS may also play some pathogenic roles in anti–synthetase syndrome by recruiting leukocytes to inflammatory cites and eliciting adaptive immune responses.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/pathogenic-role-of-tyrosyl-transfer-rna-synthetase-in-anti-synthetase-syndrome/