Anti-annexin A4 antibody as a biomarker for desquamative interstitial pneumonia

Desquamative interstitial pneumonia (DIP), a rare type of idiopathic interstitial pneumonia (IIP), is smoking-related. However, some cases of DIP can also occur in non-smokers with autoimmune disorders. The diagnosis of DIP requires an invasive surgical lung biopsy, therefore, identifying a non-invasive diagnostic biomarker for DIP is crucial. This study aimed to elucidate autoantibodies specific for DIP and evaluate their diagnostic utility. Autoantibodies in the sera of patients with DIP were screened using immunoprecipitation. The common proteins recognized by autoantibodies in patients with DIP were identified using mass spectrometry and enzyme-linked immunosorbent assay (ELISA), and compared to other types of interstitial lung diseases (ILD) and pulmonary diseases. Several characteristic proteins commonly recognized by the sera of patients with DIP were revealed using immunoprecipitation and these proteins were identified as annexin A (ANXA) proteins using mass spectrometry. Using ELISA, autoantibodies to several ANXA were detected more frequently and specifically in DIP compared with those with other types of ILDs and pulmonary diseases. In particular, anti-ANXA4 antibodies had a sensitivity of 52.6 % and specificity of 99 % for DIP compared with those of other types of ILD. Therefore, anti-ANXAs antibodies, especially anti-ANXA4, could be a candidate diagnostic biomarker for DIP.