Autoantibodies against the NineTeen complex and U5 RNP in systemic sclerosis.

ObjectiveMultiple spliceosome components are known autoantigens in systemic sclerosis (SSc). Here we aim to identify new and characterize rare anti-spliceosomal autoantibodies in patients with SSc without known autoantibody specificity. MethodsSera that precipitated spliceosome subcomplexes, as detected by immunoprecipitation-mass spectrometry (IP-MS), were identified from a database of 106 patients with SSc without known autoantibody specificity. New autoantibody specificities were confirmed with immunoprecipitation-western blot. The IP-MS pattern of new anti-spliceosomal autoantibodies was compared with anti-U1 RNP-positive sera of patients with different systemic autoimmune rheumatic diseases and anti-SmD-positive sera of patients with systemic lupus erythematosus (n = 24). ResultsThe NineTeen Complex (NTC) was identified and confirmed as new spliceosomal autoantigen in one patient with SSc. U5 RNP, as well as additional splicing factors, were precipitated by the serum of another patient with SSc. The IP-MS patterns of anti-NTC and anti-U5 RNP autoantibodies were distinct from those of anti-U1 RNP- and anti-SmD-positive sera. Furthermore, there was no difference in IP-MS patterns between a limited number of anti-U1 RNP-positive sera of patients with different systemic autoimmune rheumatic diseases. ConclusionAnti-NTC autoantibodies are a new anti-spliceosomal autoantibody specificity, here first identified in a patient with SSc. Anti-U5 RNP autoantibodies are a distinct but rare anti-spliceosomal autoantibody specificity. All major spliceosomal subcomplexes have now been described as target of autoantibodies in systemic autoimmune diseases.