<prompt> Which antibody is diagnostic of mixed connective tissue diseaseAnti-histidyl t-RNA synthetaseAnti-U1-ribonucleoproteinAnti-MyeloperoxidaseAnti-Proteinase-3  <response>: Anti-U1-ribonucleoprotein - MCTDAnti-histidyl t-RNA synthetase - Inflammatory myopathies. 