IL13 and pulmonary arterial hypertension: Arginase exists in two isoforms namely arginase I and arginase II but arginase II has been found to be much more involved in the development of PAH in humans and animals (Jin et al., 2010; Cho et al., 2013). Deletion of arginase II in interleukin-13 overexpressing transgenic mice showed a significant decrease in medial wall thickness suggesting an important role of arginase II in PAH (Cho et al., 2013).