Pulmonary hypertension (defined as systolic pulmonary pressure ≥40 mmHg) was found in four out of eleven patients (36%) in the intermediate IL-15 group, compared with one out of 31 patients (3%; P < 0.05) in the low IL-15 level group and zero out of 13 patients (0%; P < 0.05) in the high IL-15 group. This evidence concerns the gene IL15 and pulmonary arterial hypertension.