Serum-circulating His-tRNA synthetase inhibits organ-targeted immune responses.

His-tRNA synthetase (HARS) is targeted by autoantibodies in chronic and acute inflammatory anti-Jo-1-positive antisynthetase syndrome. The extensive activation and migration of immune cells into lung and muscle are associated with interstitial lung disease, myositis, and morbidity. It is unknown whether the sequestration of HARS is an epiphenomenon or plays a causal role in the disease. Here, we show that HARS circulates in healthy individuals, but it is largely undetectable in the serum of anti-Jo-1-positive antisynthetase syndrome patients. In cultured primary human skeletal muscle myoblasts (HSkMC), HARS is released in increasing amounts during their differentiation into myotubes. We further show that HARS regulates immune cell engagement and inhibits CD4+ and CD8+ T-cell activation. In mouse and rodent models of acute inflammatory diseases, HARS administration downregulates immune activation. In contrast, neutralization of extracellular HARS by high-titer antibody responses during tissue injury increases susceptibility to immune attack, similar to what is seen in humans with anti-Jo-1-positive disease. Collectively, these data suggest that extracellular HARS is homeostatic in normal subjects, and its sequestration contributes to the morbidity of the anti-Jo-1-positive antisynthetase syndrome.

The relevance of anti-Jo-1 autoantibodies in patients with definite dermatomyositis

Abstract Background: To assess the prevalence and clinical relevance of anti-Jo-1 autoantibodies in a representative sample of patients with definite dermatomyositis (DM). Methods: This retrospective cohort study took place from 2005 to 2020 and assessed 118 adult patients from a tertiary center who were diagnosed with definite DM. A commercial kit was used to detect anti-Jo-1 autoantibodies. Results: The presence of anti-Jo-1 autoantibodies was observed in 10 out of 118 (8.5%) patients with definite DM. The following variables were comparable between individuals with and without anti-Jo-1 autoantibodies: age at diagnosis, sex, ethnicity, disease duration, follow-up period, recurrence rate, complete clinical response, death rate, and cancer incidence. There was no difference in clinical features between groups, except for an increased prevalence of "mechanic's hands," joint involvement, and lung disease, as well as a reduced occurrence of skin findings in patients positive for anti-Jo-1 autoantibodies. No anti-Jo-1-positive patients went into remission; they required greater use of glucocorticoids and immunosuppressive drugs. Conclusions: Anti-Jo-1 positivity was found in 8.5% of patients with definite DM. This autoantibody was associated with an antisynthetase syndrome phenotype and might predict clinical outcomes in patients with definite DM.(AU)

Development and comparative evaluation of immunoblot assays for detecting autoantibodies to Scl 70 and Jo 1 antigens in serum.

We developed rapid 24-h immunoblot assays for detecting autoantibodies to Scl 70 and Jo 1 antigens in serum. In comparative studies, we evaluated the analytical sensitivity of the immunoblot assays and commercial immunodiffusion assays for anti-Scl 70 and anti-Jo 1 autoantibodies with the use of positive control sera, and compared the frequencies of positive and negative results in a group of 116 sera, including specimens from 34 healthy controls and 82 patients with various connective-tissue diseases. The immunoblot assays were greater than 100-fold more sensitive than immunodiffusion for detecting both autoantibodies. Despite greater analytical sensitivity, there were no false-positive results by the immunoblot assay for anti-Scl 70 or anti-Jo 1 autoantibodies in sera from either the controls or the patients. The diagnostic sensitivity of the immunoblot assay for anti-Scl 70 autoantibodies in patients with scleroderma was greater than that of the immunodiffusion assay, 70% vs 20%, and was equivalent in patients with polymyositis, 43%. We conclude that rapid immunoblot assays for anti-Scl 70 and anti-Jo 1 autoantibodies are superior to immunodiffusion assays for clinical use and are suitable for routine use in the clinical laboratory.