Identification, validation and pathogenicity of novel autoantibodies in idiopathic inflammatory myopathy.

Systemic sclerosis (SSc) and myositis, commonly referred to as idiopathic inflammatory myopathies (IIM), are rare systemic autoimmune rheumatic diseases characterized by muscle inflammation and skin fibrosis respectively, and internal organ involvement. SSc and myositis can also overlap and could thus be considered as part of a spectrum. Both diseases have a high mortality due to internal organ involvement and an association with malignancy. Within the heterogeneous SSc-myositis spectrum autoantibody-defined subtypes have been identified, leading to a timelier diagnosis, more stratified follow-up, and personalized treatment. However, in up to 30% of persons no autoantibody can be identified.

The goal of this PhD project was to identify new autoantibodies in persons with SSc or myositis without known autoantibodies and to describe potential clinical associations.

First, a new autoantigen identification method was developed based on immunoprecipitation combined with gel-free liquid chromatography-tandem mass spectrometry, or IP-MS in short. Next, with IP-MS a cohort of persons with SSc without known autoantibodies from the University Hospitals of Leuven and Ghent were analyzed. New and rare autoantibodies against telomere- and telomerase-associated proteins, as well as spliceosomal components were identified. In the same cohort, anti-RuvBL1/2 autoantibodies could be identified with an immunoprecipitation-western blot approach. The IP-MS approach was also able to identify rare autoantibodies against the complex eIF2B autoantigen in a multicenter cohort in patients with SSc. Finally, the IP-MS approach was evaluated in a group of patients with features of the antisynthetase syndrome (a subtype of myositis) with and without known antisynthetase autoantibodies. The new anti-Ly antisynthetase autoantibody was identified and rare autoantibodies against complex tRNA-synthetase autoantigens could be detected. The unbiased IP-MS approach was further successfully modified into a targeted IP-MS approach for the antisynthetase autoantibodies.

In conclusion, the newly developed IP-MS approach has led to the discovery of new autoantibodies, and detection of rare autoantibodies in SSc and myositis. The IP-MS method proved especially suitable for protein complex autoantigens. In the future, IP-MS should be further standardized and evaluated in international multicenter cohorts to establish the clinical phenotype associated with the discovered autoantibodies and identify more new autoantibodies. By further exploring the autoantibody repertoire in the SSc-myositis spectrum with IP-MS, we can work towards a personalized medicine approach for each person with SSc or myositis.