However, increased immunoreactivity for IL-7 was found in tertiary (ectopic) lymphoid tissues, i.e., highly organized perivascular follicles, in adult idiopathic PAH (IPAH) lungs, suggesting specific immune-adaptive mechanisms in the pathophysiology of the disease, at least in adults (18). This evidence concerns the gene IL7 and idiopathic pulmonary arterial hypertension.