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.
Suspected polymyositis, dermatomyositis.
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
Serum Separator Tube (SST)
Fluorescence enzyme linked immunoassay (Phadia Immunocap 250) Human recombinant Jo1 protein IgG antibodies.
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.
Results reported as negative, equivocal or positive.
5 – 7 days
Immunology The James Cook University Hospital