IFIH1 and interstitial lung disease: When individuals with MDA5+ DM-ILD were categorized into non-RP-ILD and RP-ILD subgroups, the prevalence of anti-MDA5 IgG1, IgG2, IgG3, and IgG4 was 100, 38, 29, and 19% in the RP-ILD subgroup, compared to 90, 26, 6, and 8% in the control group (Fig. 1B).