Objective: Autoantibodies directed against the aminoacyl tRNA synthetases are associated with myositis, arthritis, Raynaud's phenomenon, mechanic's hands, fever and interstitial pneumonia, clinically referred to as the anti-synthetase syndrome (ASS). The aim of this study was to characterize the autoantibody profile in a patient with clinical features of ASS whose routine diagnostic testing was negative for the previously identified anti-synthetase autoantibodies.
Methods: Serum from a patient presenting with interstitial pneumonia followed by proximal myopathy, Raynaud's phenomenon and arthrlagia was analysed for autoantigen specificity by routine methods including indirect immunofluorescence, immunodiffusion, ELISA and immunoblotting. The autoantibody specificity was further analysed by RNA and protein immunoprecipitation. Novel autoantigens found on protein immunoprecipitation were further characterized using a proteomic approach, combining immunoprecipitation, SDS-PAGE and MALDI-TOF mass spectrometry.
Results: Diagnostic testing on the patient's serum was negative by ELISA and immunodiffusion. Indirect immunofluorescence using Hep-2 cells was ANA negative, although a strong cytoplasmic speckle was seen. Immunoblotting with the patient serum displayed an unknown positive band at approximately 60 kDa. Protein immunoprecipitation revealed the presence of two proteins with molecular weights of approximately 60 and 70 kDa, and RNA immunoprecipitation revealed the presence of a band corresponding to a tRNA synthetase. Using a combination of immunoprecipitation and mass spectrometry, the novel immunoprecipitation targets were identified as phenylalanyl tRNA synthetase alpha and beta chains.
Conclusions: We report the identification of previously uncharacterized autoantibodies to phenylalanyl tRNA synthetase, entitled anti-Zo. This is the eighth anti-synthetase autoantibody in a patient with anti-synthetase syndrome.