Despite the high disease specificity of the IgA isotypes in the context of rheumatic diseases, it must be emphasized that IgA-RF can occur in other chronic inflammatory states (cirrhosis, chronic infections), and IgA-ACPA have also been found in patients with idiopathic pulmonary fibrosis where the IgA isotype was more prevalent than IgG-ACPA [49]. Here, PRTN3 is linked to pulmonary fibrosis.