Antibodies against Jo-1 are directed against the reactive site of histidyl-tRNA-synthetase (HRS) which is a cytoplasmic enzyme belonging to the group of aminoacyl transferases. These are responsible for the linking of the respepctive amino acid (for HRS it is histidine) to its cognate transfer RNA. HRS is present in the cell as homodimer; its identical subunits of approximately 50 kDa are each bound to tRNA.
Autoantibodies are commonly found in sera with myositis, and some are highly specific for this disorder. Each myositis-specific antibody defines a group of myositis patients with distinctive clinical features. About 30% of adults with myositis have antibodies to an aminoacyl transferase, and in at least 80% of cases the antibodies are directed to HRS. Anti-Jo-1 antibodies are almost exclusively found in patients with myositis. They occur in primary polymyositis with a prevalence of 33% in primary dermatomyositis with 25% and in secondary myositis associated with other connective tissue diseases with 15% prevalence. The onset of the disease is often acute with prominent systemic features such as fever. Myositis is often severe although cases without clinical muscle involvement are reported. Interstitial pneumonitis is a prominent clinical manifestation which is the next most common clinical feature after myositis in anti-Jo-1 positive patients, being present in 50-90% compared to <10% of other patients with polymyositis or dermatomyositis.
Other myositis-specific antbodies have been detected (prevalence <5%): e.g. antibodies against threonyl-(anti-PL-7), alanyl-(antiPL-12), iusoileucyl-(anti-OJ) anbd glycyl-tRNA synthetase (anti-EJ).
Method:
Immunoenzymatic method for the semiquantitative determination of IgG class antibodies to human histidyl-tRNA synthetase (Jo-1) in human serum, using a disposable device applied on the Chorus and Chorus TRIO instruments. The test is based on the ELISA principle (Enzyme Linked ImmunoSorbent Assay) which uses the reaction between the antibodies present in the tested sample and the immobilized antigen bound to solid phases.The immunoglobulins bind to the antigen through incubation with diluted human serum.The disposable devices contain all the reagents to perform the test when applied on the Chorus instruments. The Chorus Jo-1 is calibrated against reference sera from the CDC (Atlanta). The results are expressed in AU/ml.
