MUC5B and rheumatoid arthritis: Furthermore the presence of rheumatoid factor (RF) and/or anti-citrullinated protein antibodies (ACPA), a genetic predisposition, e.g., MUC5B promoter variant rs35705950, high levels of matrix metalloproteinase-3 and other extra-articular manifestations of RA like subcutaneous rheumatoid nodules or secondary systemic sclerosis show an association with an increased risk for RA-ILD [15–17].