IntroductionRecent studies have identified circulating IgG autoantibodies against cytoplasmic 5'-nucleotidase 1A (cN1A; NT5C1A) in patients with inclusion body myositis (IBM), whose detection provides for an IBM blood diagnostic test. Whether or not anti-cN1A autoantibody isotypes other than IgG are present in IBM has not previously been reported.MethodsPlasma and serum samples from 205 patients (50 with and155 without IBM) were studied for the presence of IgM and IgA, in addition to IgG, anti-cN1A autoantibodies using immunoblots and enzyme-linked immunoassays (ELISAs).ResultsIgM, IgA, and IgG anti-cN1A autoantibodies were detected by ELISA with similar sensitivities (49-53%) and specificities (94-96%), b... More
IntroductionRecent studies have identified circulating IgG autoantibodies against cytoplasmic 5'-nucleotidase 1A (cN1A; NT5C1A) in patients with inclusion body myositis (IBM), whose detection provides for an IBM blood diagnostic test. Whether or not anti-cN1A autoantibody isotypes other than IgG are present in IBM has not previously been reported.MethodsPlasma and serum samples from 205 patients (50 with and155 without IBM) were studied for the presence of IgM and IgA, in addition to IgG, anti-cN1A autoantibodies using immunoblots and enzyme-linked immunoassays (ELISAs).ResultsIgM, IgA, and IgG anti-cN1A autoantibodies were detected by ELISA with similar sensitivities (49-53%) and specificities (94-96%), but with differing patterns of autoantibody isotype presence. Combination assays of all 3 autoantibody levels improved diagnostic sensitivity to 76%.DiscussionIn addition to previously recognized IgG anti-cN1A autoantibodies, IBM patients have circulating IgM and IgA anti-cN1A autoantibodies. Differing patterns of these isotypes may be present and useful for diagnosis.
