We used this model to reveal that serum SP‐D is a suitable marker of lung damage in RA‐ILD (Figure S1 and Figure 3K), similar to serum SP‐A, SP‐D and Krebs von den Lungen‐6 as markers of idiopathic interstitial pneumonias in humans.33 This evidence concerns the gene SFTPD and rheumatoid arthritis.