SDC2 and pulmonary fibrosis: To study the in vivo role of SDC2 in RA-ILD, we developed a two-hit model in which we utilized the combination of collagen antibody-induced arthritis (CAIA)37, a previously validated mouse model of inflammatory arthritis characterized by administration of collagen type II autoantibodies and lipopolysaccharide (LPS)38–40, followed by lung injury with bleomycin to induce pulmonary fibrosis (Supplementary Fig. S6 online).