Jo-1 Antibody

What is Jo-1 Antibody?

Detects autoantibodies against histidyl-tRNA synthetase, most often associated with antisynthetase syndrome and myositis.

Jo-1 antibodies (anti-histidyl-tRNA synthetase) belong to a family of myositis-specific autoantibodies studied when a clinician suspects an inflammatory myopathy such as polymyositis or dermatomyositis. They relate primarily to the muscular, pulmonary, and immune systems, since Jo-1 positivity is closely linked with antisynthetase syndrome, a condition that can combine muscle weakness, interstitial lung disease, joint inflammation, and skin changes. Clinicians commonly order this test in people with unexplained muscle weakness, elevated muscle enzymes, or lung findings suggestive of an autoimmune process, often alongside other myositis-specific and myositis-associated antibodies. Because Jo-1 antibodies are relatively specific but not universally present in every case of myositis, results are interpreted together with clinical exam findings, imaging, and sometimes muscle biopsy rather than as a stand-alone diagnostic answer.

Tests often checked alongside this

• Muscle enzymes (CK, aldolase) — help assess muscle inflammation alongside antibody findings
• ANA (Antinuclear Antibody) — a broader screen often checked when myositis-specific antibodies are considered
• Other myositis-specific antibodies (PL-7, PL-12, EJ, OJ) — part of the antisynthetase antibody family
• Inflammatory markers (ESR, CRP) — reflect overall inflammatory activity

How this can show up in how you look and feel

• May be associated with muscle weakness or fatigue in some individuals
• May be associated with joint pain or stiffness
• May be associated with respiratory symptoms such as shortness of breath or a persistent cough
• May be associated with skin changes such as rough, cracked skin on the fingers (sometimes called "mechanic's hands")

What can affect this marker

• Age
• Sex
• Inflammation
• Medications (certain immunosuppressive therapies can lower antibody levels)
• Lab variability between testing methods

What to track over time

• Whether levels trend alongside muscle enzyme changes over time
• Correlation with respiratory function tests if lung involvement is a concern
• How results align with symptom changes reported to a healthcare professional
• Repeat testing may be considered if new muscle or lung symptoms develop

What to ask your doctor

• What does a positive or negative Jo-1 result mean in my specific situation?
• Should this be interpreted alongside muscle enzyme or lung function testing?
• Are there other myositis-specific antibodies worth checking?
• What symptoms should prompt me to seek follow-up?

This glossary entry is for informational purposes only and is not a substitute for professional medical advice. Read our Terms of Use.