a measurement of autoantibodies that are specific for histidyl-tRNA synthetase, also known as Jo-1; found in up to 25% of patients with myositis. This cytoplasmic enzyme catalyzes the esterification of histidine to its cognate tRNA. Binding of anti-Jo-1 antibodies is localized to the cytoplasm of various cell types and the binding can be visualized by immunofluorescence. The test used to detect the autoantibodies in serum is usually an enzyme-linked immunosorbent assay.