Pulmonary arterial hypertension (PAH) is a severe condition characterized by vasoconstriction and remodeling of the small pulmonary arteries, driven by a complement-dependent activation of macrophages, for which an effective treatment is lacking. Chinese researchers have investigated the potential of a complement C3 inhibitor polypeptide, CP40-KK, as an approach for treating PAH. To do this, they used a model in which PAH was induced in rats by monocrotaline.