Identification of connective tissue disease autoantibodies and a novel autoantibody anti-annexin A11 in patients with “idiopathic” interstitial lung disease

Autoantibodies are a hallmark feature of Connective Tissue Diseases (CTD). Their presence in patients with idiopathic interstitial lung disease (ILD) may suggest covert CTD. We aimed to determine the prevalence of CTD autoantibodies in patients diagnosed with idiopathic ILD. 499 patient sera were analysed: 251 idiopathic pulmonary fibrosis (IPF), 206 idiopathic non-specific interstitial pneumonia (iNSIP) and 42 cryptogenic organising pneumonia (COP). Autoantibody status was determined by immunoprecipitation. 2.4% of IPF sera had a CTD-autoantibody compared to 10.2% of iNSIP and 7.3% of COP. 45% of autoantibodies were anti-synthetases. A novel autoantibody targeting an unknown 56 kDa protein was found in seven IPF patients (2.8%) and two NSIP (1%) patients. This was characterised as anti-annexin A11. Specific guidance on autoantibody testing and interpretation in patients with ILD could improve diagnostic accuracy. Further work is required to determine the clinical significance of anti-annexin A11. •Anti-annexin A11 is present in 2.8% of patients with idiopathic pulmonary fibrosis.•Anti-Annexin A11 was also found in patients with idiopathic NSIP, SLE and myositis.•CTD autoantibodies were present in up to 10% of patients with idiopathic ILD.•Most CTD autoantibodies identified were readily detectable using routine assays.