Antibodies to the Jo-1 antigen (histidyl-tRNA synthetase^1,2) are found in approximately 30% of adult patients with myositis (including polymyositis, dermatomyositis and overlap syndromes) and are particularly common (~60%) in patients with both myositis and interstitial lung disease (cryptogenic fibrosing alveolitis or pulmonary interstitial fibrosis).^1-5 Jo-1 antibodies are most commonly found in addition to other aminoacyl synthetases [threonyl (anti-PL-7), alanyl (anti-PL-12), isoleucyl (anti-OJ) and glycyl (anti-EJ)] in patients with the anti-synthetase syndrome which is characterized by acute onset, steroid-responsive myositis with interstitial lung disease, fever, symmetrical arthritis, Raynaud phenomenon and mechanic's hands.^6-8 Recent studies have shown anti-Jo-1 as the most commonly detected myositis specific antibody (MSA), followed by anti-synthetase, anti-Mi-2 and anti-SRP antibodies, with an association identified between Jo-1 and anti-RO52, a myositis-associated antibody (MAA).⁹ The presence of Jo-1 antibodies in idiopathic polymyositis patients is usually accompanied by severe disease, tendency to relapse and poor prognosis.⁶ Muscle pathology of patients with anti-Jo-1 antibody-associated myopathies reveals perimysial connective tissue fragmentation and inflammation along with muscle fiber pathology in nearby perifascicular regions.¹⁰  In juvenile myositis with Jo-1 autoantibodies, the clinical manifestations, disease course and response to therapy closely resemble those in adults; however, frequency studies are lacking.¹¹

EIA using native or recombinant antigen and immunoblot using HeLa cell extract are reported to have higher specificity and sensitivity than double immunodiffusion, enzyme inhibitor activity and IFA.^12-15 However, specimens negative by immunodiffusion but positive by EIA are uncommon.² The use of Tween 20 in the immunoblot procedure significantly improves the binding of autoantibodies to Jo-1, Scl70, U1RNP and others.¹⁶ Consensus sera are now available to clinical laboratories and vendors for use in the detection of Jo-1, SS-A, SS-B, Sm, double-stranded DNA, U1-RNP, Scl-70 and centromere antibodies to help evaluate and improve current EIA, Ouchterlony, and immunofluorescence assay methods.¹⁷ Antibodies to a 56 kd protein are found in 85% of patients with myositis; antibody levels might reflect disease activity in adults.¹³ D-penicillamine-induced polymyositis occurs in rheumatoid arthritis at a greater frequency than idiopathic polymyositis; withdrawal of the drug usually coincides with disappearance of Jo-1 antibodies and other antibodies (ANA) and clinical improvement.¹⁸ An association between HCV infection, Jo-1 antibodies and polymyositis is recognized.¹⁹ The first report of a patient suffering from polymyositis with the anti-Jo-1 antibody who survived acute respiratory distress syndrome after intravenous pulse cyclophosphamide therapy was recently published.²⁰