Although previous studies have investigated the relationship between serum KL-6 levels and disease activity/severity as well as prognosis in SSc–ILD [29–31], RA-ILD [30, 32, 33], and PM/DM-ILD [30, 32], we found that KL-6 also related to severity of pSS–ILD. Here, MUC1 is linked to systemic sclerosis.