Anti-Jo-1 Antibodies

Autoimmune myopathies are a heterogeneous group of chronic inflammatory diseases of the skeletal muscle, characterised by proximal muscle weakness, increased muscle enzymes (e.g., CPK), electromyography (EMG) abnormalities, compatible muscle biopsy and the presence of myositis-specific (MSA) or myositis-associated (MAA) autoantibodies. Main forms include dermatomyositis (DM), polymyositis (PM), necrotising autoimmune myopathy (NAM) and inclusion body myositis (IBM).

Among MSAs, anti-Jo-1 antibodies—directed against histidyl-tRNA synthetase, a cytoplasmic enzyme involved in protein synthesis—play a key role. Anti-Jo-1 are strongly associated with anti-synthetase syndrome, a clinical subtype of IIM characterized by myositis, non-erosive arthritis, Raynaud’s phenomenon, “mechanic’s hands” and interstitial lung disease (ILD).

Given their high diagnostic specificity, anti-Jo-1 are the only myositis-specific autoantibodies included in the 2018 ACR/EULAR classification criteria. Their presence increases the classification score and supports the diagnostic probability of IIM, compared with other autoantibodies (e.g., anti-Mi-2, anti-SRP, anti-PL-7, anti-PL-12) that have not met the evidence threshold for inclusion.

Although they are specific markers for myositis, anti-Jo-1 antibodies are also relevant for SARDs, particularly in overlap syndromes. Serological characterisation helps identify distinct clinical phenotypes useful for risk stratification, therapeutic management and prognosis.