Alternative name: Anti-tRNA Synthetase
Description: The Jo1 system was described in association with polymyositis and is an important marker antibody for this disease. The antigen is Histidyl-tRNA synthetase. Other aminoacid tRNA synthetases are also recognised by other polymyositis associated autoantibodies. These autoantibodies give diffuse granular cytoplasmic staining on Hep-2 cells. Other autoantibodies recognising antigens known as Mi-1, Mi-2, Ki and Ku are also associated with polymyositis or polymyositis-scleroderma overlap.Jo1 is referred to as an extractable nuclear antigen though it is primarily a cytoplasmic antigen. Anti-Jo1 is detected in the ENA screen. It is found in 25% cases of polymyositis and correlates with presence of pulmonary fibrosis. Jo1 is one of a number of related autoantigens associated with polymyositis.The Jo1 antigen, histidyl tRNA synthetase is a cytoplasmic enzyme which incorporates histidine into growing polypeptide chains. The antigenic determinants appear to be somewhat conformational but are detected by immunoblotting. Other myositis-related autoantibodies recognise alanyl, threonyl and other tRNA synthetases – at present we are unable to test for these antibodies. However please contact the laboratory if you believe these tests would be of value.
Indication: Suspected polymyositis, dermatomyositis.
Interpretation: Antibodies to Jo1 are found in 20-60% patients with primary polymyositis or dermatomyositis and less commonly in association with other connective tissue disease. Anti-Jo1 positive patients tend to have the poorest prognosis with more prominent lung involvement and less skin involvement. Anti-Jo1 is often found along with other ENAs particularly anti-Ro52
Sample: Serum Separator Tube (SST)
Assay details: Fluorescence enzyme linked immunoassay (Phadia Immunocap 250) Human recombinant Jo1 protein IgG antibodies.
Restrictions: Jo1 is difficult to detect by immunofluorescence and therefore can be missed in the anti-nuclear assay. It should be requested specifically where (dermato-) myositis is suspected. Test is only carried out when ENA screen is positive.
Reference range: Results reported as negative, equivocal or positive.
Assay range Notes:
Turnaround time: 5 – 7 days
Analysing laboratory: Immunology The James Cook University Hospital