IL6 and pulmonary arterial hypertension: Recently, Simpson analyzed data, which was from the PAH biorepository of the National Institutes of Health and the National Heart, Lung, and Blood Institute, and found that IL-6 is upregulated to varying degrees in different PAH subtypes, with the highest levels observed in connective tissue disease-related PAH (CTD-PAH) and portopulmonary hypertension [169].