DLCO: diffusing capacity for carbon monoxide; ET-1: endothelin-1; ETAR: endothelin type A receptor; ESR: erythrocyte sedimentation rate; IFN: interferon; IgG: immunoglobulin G; IgM: immunoglobulin M; ILD: interstitial lung disease; IL-6: interleukin-6; PH: pulmonary hypertension; RF: rheumatoid factor; RNP: ribonucleoprotein; Scl-70: topoisomerase I antibody; SLE: systemic lupus erythematosus; Sm: Smith antibody; SSA (Ro): Sjögren’s-syndrome-related antigen A. This evidence concerns the gene IL6 and pulmonary arterial hypertension.