IL18 and pulmonary arterial hypertension: In 2020, Zhang et al. reported that the expression levels of interleukin-18 (IL-18), cysteine protease-1 (caspase-1), and high mobility group protein B1 (HMGB1) transcripts and proteins were elevated in the lung tissues of the MCT-induced PAH model rats; this linked pyroptosis to the upregulation of the programmed death receptor 1 (PD-1) in the human PASMCs 7.